Proceedings of the 14th International Conference on the Technology of Plasticity - Current Trends in the Technology of Plasticity

Due to current global challenges regarding energy security as well as climate change the importance of preserving the nature and all available resources is steadily increasing. In order to achieve the energy-saving and climate targets, it is not only necessary to develop new processes and processing possibilities, but also to optimise known process chains with regard to energy and resource efficiency in the area of production technology. Here, the recycling of supposed production waste represents an opportunity to save energy. In addition to the conventional and smelting metallurgical recycling process, extensive research activities have therefore been carried out for alternative solid-state recycling processes. One example is the friction-induced recycling process, which has been used in past studies to demonstrate the energy- and resource-efficient production of semi-finished products from aluminium scrap such as chips. In addition, properties like chemical composition and strength can be adjusted locally and in terms of processing time. This can be used to improve the versatility of further processing steps.In this paper, starting from the successful forming of auxiliary joining elements from the recycled semi finished product, a comparison is aimed with auxiliary joining elements made from conventionell produced semi finished products. The evaluation of the mechanical properties of the joint connections produced in a second step shows that recycled semi-finished products exhibit comparable properties. This implies the production-technical suitability of secondary metals and opens up broad potentials for improving the versatility of joining processes through property grading in solid-state recycling processes.

Al/Steel composite plate has broad application prospects. In this paper, Al/Steel composite plates with high bonding strength were prepared by cold rolling through oxidation treatment of steel surface. The results show that the steel side oxidation treatment can effectively improve the bonding strength of Al/Steel composite plates. The shear strength of “wire brush grinding + steel side oxidation”(‘WSO’) and the process without oxidation are 89 MPa and 53 MPa, after annealling. The mechanism analysis shows that the brittle oxide on the steel plate surface forms cracks during rolling. When the fresh metal on the aluminum side is squeezed into the crack on the steel side, it contacts with the fresh metal on the steel side to form a high-strength bond and form an effective mechanical bite.

A new impact joining method of metal plates was demonstrated. The plate edges to be joined slides at a high-speed with increasing compressive force, which gives rise to a large plastic deformation for the material near the sliding interface. The test materials were a pure copper C1100-1/4H and an aluminum alloy A6061-T6 with a thickness of 5 mm. The similar material or dissimilar ones were combined. The objective is to show the possibility of this method. The energy source for the impact joining was the drop-weight of about 90 kg, whose impact velocity or the initial sliding speed was 10 m/s. Tensile test of the joined plate was performed, where the force was applied perpendicular to the joint boundary. The joining was not achieved for the full thickness. The joint efficiency was evaluated along the joint boundary for the initial thickness of the plate. Hence it was somewhat underestimated. The joint efficiency of C1100 - A6061 joining was 50% or more over about 70% part of the joint boundary. Since the A6061 material was adhered over the surface of C1100 at the fractured surface, the boundary is quite strong. The joint efficiency of C1100 - C1100 or A6061 - A6061 joining was about 70% except for the end portions of the joined plate.

The joining of metallic and thermoplastic components offers the possibility of weight reduction with a simultaneous increase in functionality, whereby the determination of the joint strength is of special interest. In the context of this study, the use of resistance-based sensors for joining by hydraulic expansion of tubes made of aluminum and polycarbonate was investigated. The contact pressure, determined in time and spatial resolution, was used to determine the axial load transferability and compared with the common methodology of the pull-out test. By using this measurement method, it was possible to determine the influence of the force- and form-fit onto the joint strength.

Ni-base superalloys are widely used for thin-wall components that need to resist high-temperature environments in aero-engines and high-speed aircraft. Hence, their mechanical properties and microstructures after laser welding at high temperatures are essential to be investigated and evaluated. In this study, the evolution of main mechanical properties (including the yield strength, and tensile strength) and microstructures of laser-welded Ni-based superalloy and base metals (BM) under tensile deformation at different temperatures (20 ℃, 300 ℃, 500 ℃) are investigated and compared. The tensile strength results indicate that the strength of the welded part is slightly higher than that of the BM at room temperature, while the results turn to the opposite trend with increasing temperatures. The microstructural results suggest that evolutions of carbide precipitates and grain sizes in the welded joint under different temperatures concurrently affect the strength. At 20 ℃, the strengthening effect from carbide precipitates after welding is more apparent, leading to a slightly higher stress level in the welded alloy; while at 300 ℃ and 500 ℃, the softening effect caused by the increasing grain sizes in the welded alloy plays the dominant role, leading to the reduction of strength after welding.

For the press hardening process an Al-Si coating is usually applied on the surface of typical boron-manganese steels (22MnB5), to form a diffusion layer for protection against scaling. However, the diffusion layer requires long heating times and is environmentally questionable. This paper describes a new approach to substitute the Al-Si coating by a stainless steel (X5CrNi18–10) to provide an environmentally friendly alternative, save heating energy and raise the production efficiency. For this, the hot roll bonding of 22MnB5 and two protective layers of X5CrNi18-10 to produce laminated composites are investigated by experiments and FE-simulations. The aim is to set up a computer-aided design of the hot roll bonding using a calibrated isothermal bond strength model and to validate it by hot roll bonding experiments. Firstly, the bonding properties of the material combination 22MnB5/X5CrNi18-10 are characterized at 1000 ℃ in a lab scale experiment. With those truncated cone tests an isothermal bond strength model is parametrized by bond strength measurements at different height reductions and stress states. Secondly, the contact parameters are calibrated by the simulations of the truncated cone tests. With the calibrated contact parameters, the experimental compression and de-bonding forces are reproduced by the simulations with a general deviation of 15%. Finally, the calibrated contact parameters and the bond strength model are implemented into the hot roll bonding process model of the first two rolling passes. According lab-scale roll bonding experiments are performed to validate the simulations. A comparison of the rolling forces as well as layer thicknesses after each pass show a good agreement between the simulations and experiments.

Magnetic Pulse Welding (MPW) is a high-velocity impact welding technique that allows the joining of dissimilar materials such as aluminium and copper. Welding should be produced under the appropriate conditions: impact velocity (200–500 m.s−1) and collision angle (10–30°). The formation mechanisms leading to the welding creation are not very clear. This work investigates the microstructure and hardness at the interface to understand these mechanisms.Al/Cu and Cu/Cu samples were formed with identical process parameters. They were first compared to the literature using Vickers microhardness. Obtained results are standard and correspond to previous studies. In a second step, a detailed characterization of the interface using nanoindentation and electron back-scattered diffraction (EBSD) methods is done.Different behaviors were found at the interface between Al/Cu and Cu/Cu. Al/Cu exhibited a thin layer of intermetallic compounds (IMC), increasing the hardness at the interface. This layer was composed of Al2Cu and Al4Cu9 compounds, as demonstrated by Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD). Cu/Cu presented a dissimilar behavior at the interface. The flyer sheet shows an increase in hardness due to grains deformation and distortion. While, the base sheet manifested a decrease in hardness caused by dynamic recovery or recrystallization at the interface. In both cases, the samples were deformed and hardened due to the plastic deformation induced during impact. These results are complementary to previous studies. They provide new insights that could be used to improve our understanding of the mechanisms behind such high-velocity impact welding.

The use of stainless steel with high strain hardening as material for self-piercing rivets is a promising approach to shorten the manufacturing process. Due to the corrosion resistance of the material and the achieved high strength within the forming process, the heat treatment and the coating can be omitted. As the strength within the rivet material is achieved by cold forming, the strength distribution within the rivet remains intact after the manufacturing process. The aim of the contribution presented is the exploitation of the potential of this strength distribution to improve the performance of the self-piercing rivets. Therefore, the scope of the examination is on the analysis of the influence of the local strength on the deformation behaviour of the rivet during joining. While it is unfeasible to manufacture rivets with any desired strength distribution, numerical simulation offers an efficient opportunity to study the effects of varying local strengths. By using a definable true strain distribution within the rivet as presetting for the simulation, different strength distributions can be modelled. Through the simulation of the joining process, the deformation behaviour of the rivet can be examined. Based on the insights of this analysis, a strength distribution is created that supports the joining of challenging material combinations consisting of high strength steel and aluminium. Finally, the approach is verified by experimental joining tests.

Lightweight construction is a powerful tool for reducing energy consumption in modern automotive engineering. Mechanical joining technology such as clinching is increasingly being used to implement different types of lightweight materials in the body-in-white. In addition, numerical dimensioning is gaining in importance in the development process. While clinching with a rigid die can be simulated realistically using a 2D axisymmetric simulation, it is not feasible for extensible dies due to geometry and kinematics of the die-intern lamellae, which do not fulfill the assumption of axial symmetry. Therefore, a 3D simulation is necessary. Clinching with extensible die creates a joint, which has a varying neck thickness - undercut profile depending on the microsection direction. To predict the joint geometry, a comprehensive experimental parameterization is necessary for clinching with a rigid die, as recent studies have shown. The aim of this investigation is to parameterize the joining process in terms of friction and to develop a predictive 3D-simulation. Two novel friction test beds are used to investigate the tribological conditions in the process. On the one hand, a rotational test bed is used to identify the friction conditions between tools and joining parts, on the other hand, a translational friction test bed is used to parameterize the die-internal contact between lamella and die running surface. Based on the experimental friction investigations a 3D joining process simulation is carried out and compared to experimental joints. For this purpose, process curves and microsections are used as comparative instruments. The investigations are providing the basis for the process chain simulation of clinching with extensible die.

This article is focused on the utilization of a joining by plastic deformation process known as double-sided injection lap riveting to fabricate aluminum busbar connections for energy transmission and distribution systems. Special emphasis is placed on a new cutting tool concept capable of machining the dovetail ring holes, which will later be filled by the injection of aluminum rivets to create form-closed joints. The methodology is based on the design, construction, and utilization of a flexible, modular, cutting tool for machining dovetail ring holes in metallic busbars. Experimental work validates the cutting tool concept, identifies the main operative parameters, and fabricates busbar connection samples by double-sided injection lap riveting, whose performance is then evaluated by means of thermo-electrical testing. Numerical modelling with finite elements gives support to fabrication and thermo-electrical characterization of the aluminum busbars connections. Comparisons are made against conventional busbar bolted joints.

Adhesive bonding plays an increasingly important role in joining metallic bipolar plates of hydrogen fuel cell due to high manufacturing efficiency and small deformation with comparison to other joining technologies (e.g. laser welding, sealing gasket), however, tremendous difference in surface physiochemical properties results in poor bonding compatibility between metallic polar plate and adhesive, which remains a challenge to the wide application of adhesive bonding technology. In this study, titanium bipolar plate with excellent corrosion resistance and high specific strength was laser-treated to modify its surface physiochemical properties for the improvement of interfacial bonding compatibility. Results indicate that laser surface modification enable a maximum improvement of ~130% on bonding strength of titanium bipolar plate with comparison to untreated condition. In addition, the effects of laser processing parameters (e.g. overlap ratio, laser power, aspect ratio) on bonding strength were investigated through orthogonal experiments. It is found that overlap ratio exhibits a more significant effect on bonding strength than laser power, and the weakest effect was observed for aspect ratio. On the premise of ensuring the improvement of bonding strength, we further optimized processing parameters of laser power and overlap ratio to decrease laser input energy to avoid large thermal deformation of titanium bipolar plate, since laser input energy was determined by pulse energy and energy density, corresponding to laser power and overlap ratio, respectively. At the end of this work, laser processing parameters were optimized for adhesive bonding of titanium bipolar plate.

In the development of innovative lightweight solutions in automotive engineering, the use of the mechanical joining technique clinching offers the possibility of joining mixed structures with a wide range of requirement profiles. In order to be able to predict the material failure behavior of clinched structures under crash-like scenarios and to design components accordingly, investigations of the load-bearing behavior of clinched joints under high strain rate loading are necessary. For this reason, shear tensile tests on clinched joints under impact load application are to be carried out and evaluated with regard to their load-bearing capacities within the scope of this work using the aluminum alloy EN AW-6014 T4. In addition, the influence of plastic preforming of the parts to be joined is investigated. Furthermore, corresponding numerical investigations are carried out, for which the strain rate dependency of the material's plasticity is first characterized experimentally and implemented in the material model. Subsequently, the experimentally and numerically determined load-bearing capacities of the clinched joints are compared and discussed.

Many engineering applications require hollow structures that are completely sealed, such as tubes with closed ends. In this study axial plugs or caps are inserted during the forming process to provide a pressure-tight seal. Joining the sealing element and tube by plastic deformation represents one possible process route. Its advantages include the ability to join different materials and the low heat input. Rotary swaging is particularly suitable as it allows for undercuts, resulting in high joint strength.In this study, infeed and forward rotary swaging are used. The material combinations analysed were different grades of steel, aluminium alloys and brass. Additionally, the influence of different undercuts and additional sealing materials is investigated. Comprehensive experimental investigations are carried out in addition to a numerical study. The joint is evaluated by pressure tests, metallographic examinations of the joint zone and an analysis of the material flow. To delineate the process window, failure modes such as cracks of the pipe, insufficient undercuts or excessive deformation of the sealing element are investigated based on the variation of process and material parameters.The process principle is discussed for two applications with different requirements in terms of initial geometries and loads. Firstly for the production of Nd-Fe-B permanent magnets by rotary swaging as an alternative to the conventional sintering process. Secondly for a curved phase change actuator based on paraffin wax. A rectangular tube is to be formed axially symmetrically and sealed with a sealing element against pressures well above 100 bar.

A shape of teeth for serration joining was optimized to improve joining strength as well as to reduce joining load. The serration joining has been proposed to manufacture an automobile shaft with a large disk. The shaft and the disk were joined through the following three processes: a) extrusion of a shaft with serration, b) carburizing of the only outer side including the teeth of the serration, c) penetration of the serrated shaft into a holed disk for joining. Filling up to the teeth shape and strain hardening due to plastic deformation by teeth indentation is a key factor to increase the torsional strength after joining. In this study, experiments about typical tooth shape using clay model brought a rough but nevertheless fundamental result of the valuable top shape of the tooth. Moreover, numerical analyses by FEM were also tried about the several teeth shapes. Thus, it was found that a tooth with a one-side wedge & a small round top enables the joining region to provide large strain by a low joining load.

The automotive industry achieves lightweight designs through the use of multi-material designs, which present challenges in joining and have led to an increased use of mechanical joining techniques. Clinching, as a mechanical joining process, has become a common technique in many areas of the automotive industry. To predict the relevant properties of clinched joints, the entire process chain is numerically simulated during the product development process. The accuracy of the predicted results strongly depends on the implemented friction model. The process chain of clinching is modeled in a finite element simulation, which represents different process steps such as joining and shear tensile loading. By coupling these different process steps, relevant values from the joining process can be transferred to the loading simulation. Using a friction subroutine, contact-relevant variables can be calculated along the process chain, and their influence on individual steps can be investigated. The aim of the study is to demonstrate the development of locally different friction-relevant parameters (such as friction displacement) along the clinching process chain.

Electromagnetic forming offers high potential for producing high-quality joints of similar and dissimilar materials. This can be exploited e. g. in aircraft design for assembly of struts. In order to give insight in the interactions between different influencing parameters and their effect on the loadability of the resulting joint in electromagnetic form-fit joining, design of experiments was used in a comprehensive study. Groove parameters (shape, depth, width and edge radius) and the capacitor charging energy were varied in joining experiments considering tubes made of EN AW-2024 (T351) with an outer diameter of 70 mm and, a wall thickness of 1.6 mm together with end parts made of the same material with a diameter of 66.8 mm. The loadability of the resulting compound was evaluated considering axial compression force. One important finding was that triangular grooves can provide highest loadability if relatively deep grooves, well-adjusted groove width and suitable capacitor charging energy are applied. An optimized groove edge radius can contribute to further improvement of the loadability. Numerical simulations on different groove shapes were performed in order to study the development of the forming stages during the process and to explain the trends observed in the experimental study.

Friction stir welding (FSW) is a renowned joining technology for creating difficult-to-be-welded or non-weldable dissimilar material joints engendering viscoplastic material flow at the interface. The present work compares the evolution of the material flow and properties during FSW of extremely different materials, viz., Aluminum alloy 6156 and commercially pure Ti Grade 2 with the help of numerical simulation and practical. The necessity of the appropriate heat flux to be achieved through balancing parameters was realized through simulation and experimental outcomes. In the paper, a numerical model is presented to predict the main field variables distribution and the resultant material flow during FSW of dissimilar Al-Ti skin stringer joints. Valuable insights relating to material flow patterns observed while altering the mutual skin stringer positions have been elaborated. Macrostructural and microstructural characterizations were carried out to understand the localized material microstructural evolution comprising grain refinement, intermetallic, defects, etc. The parametric influence on grain morphologies, intermittent phases, joint strengths, and hardness are discussed in depth. Interestingly, the joint strength values recorded for prepared T-joints are comparable with the ones found for butt joint configurations reported in the literature.

Shape memory alloy (SMA) pipe couplers offer a promising way to improve the reliability of pipe joints in various industrial applications. However, the deformation behavior of SMA during multistage joining processes, such as radial expansion at cryogenic temperature, is complex. Here, the experiments are conducted for Ni47Ti50Fe3 under different thermal-mechanical loading conditions to reveal the deformation mechanism of SMA during the tube joining process. Then, the constitutive model of SMA is numerically implemented into the finite element simulation (FE) to represent the whole joining process, so that the structure of the coupling can be optimized and subsequently fabricated. The connection patterns of the SMA pipe couplings are fabricated. By comparing the deformation of the pipe in the simulation and the test results, the simulation results are verified.

Numerical simulations of welding processes, although a quite complex modelling and calibration is required, can be a powerful tool to reduce both design time and costs ascribable to experimental tests. Indeed, numerical simulations allow prediction of distortions and residual stresses on welded joints related to the thermal process effects. This paper focuses on a numerical modelling and simulation of a multi-pass submerged arc welding process performed on a butt joint configuration of A516 steel plates with different thicknesses. The numerical analysis was performed by using the software package ESI SYSWELD. This software simulates welding processes by three different methods, depending on the objectives to be reached, i.e. the moving heat source, the macro-bead and the shrinkage methods. These methods differ mainly in the thermo-mechanical data of the material provided as inputs for the model definition and, consequently, for the considered physical phenomena. Herein, these three different approaches were implemented for the specific process configuration. The obtained results were compared providing a wide overview of the most suitable numerical strategies evaluating the distortions and the residual stresses induced in the investigated joined parts. The methods’ comparison includes also considerations on computational times required to perform the analysis.

In the aim to set up a robotized assembly process, this article studies the feasibility of Friction Forge Riveting (FFR) for industrial application as it can be considered as a good alternative for reinforcing multi-material assemblies. A finite element study is developed using Abaqus® and it enables the deformation of a cylindrical bar into the shape of a rivet by friction. The sensibility of the assembly parameters is taken into account in this study. A thermomechanical axisymmetric model for an aluminum rivet formed by a tungsten-lanthanum tool is proposed. A remeshing algorithm developed using Python is used in the simulation because of the large strain induced during the process. The simulation of the thermomechanical behavior of the rivet is important for the improvement of this innovative process. Experimental studies were developed in a CNC machine and the force and temperature data is compared with the simulation.

In the last decade have been developed many hybrid metal forming processes that foresee the integration of commonly used sheet metal forming processes, such as bending, deep drawing, spinning, and incremental forming, with the metal additive manufacturing process as the Powder Bed Fusion technology Selective Laser Melting. These integrations have been developed more in the productive sectors characterized by the request of components with complex geometries in small numbers such as, for example, the aerospace sector. Hybrid additive manufacturing overcomes the typical limitations of additive manufacturing related to low productivity, metallurgical defects, and low dimensional accuracy and promotes new applications with traditional manufacturing processes. In this perspective, obtaining parts characterized by high strength and ductility becomes a key aspect in the development of hybrid processes. In the present work samples of Ti6Al4V alloy were printed using the SLM additive manufacturing technology and the influence of process parameters, such as the Linear Energy Density on the ductility of material was studied. The characterization of the samples was performed through tensile tests to determine the mechanical characteristics of the material and by OM analysis of the fracture surface of tensile tested specimens. Further density analysis, using the principle of Archimedes, allowed quantifying the porosity defects.

This paper presents a new hybrid additive manufacturing approach to design and produce innovative collector coins from customized blanks with asymmetric, small, intricate holes that cannot be obtained from blanking, laser, or water jet cutting. The approach starts with the construction by laser powder bed fusion of the cylinders from where the individual blanks are obtained through wire electro-discharged machining. The individual blanks are subsequently polished and subjected to a coin minting operation to emboss the final letters, details and finishing of the designs. Experimental tests in a press-tool system and numerical simulations of the coin minting operation using an in-house finite element program were carried out with a case study developed in collaboration with the Portuguese Mint. The combined numerical and experimental investigation allows validating the developed approach by proving its feasibility for the production of high value-added silver collector coins aimed at redefining the standards of creativity and security in the numismatic market.

For those large-size components used in oil, chemical, aerospace, or nuclear industries, a novel solid-state additive manufacturing(AM) by piling up and bonding pre-shaped thick plate layers appears as a potential technology [1]. Apart from high efficiency and lower materials wastage, solid-state AM can avoid some solidification defects in traditional AM, like hot cracks and dendritic microstructure. The sound bonding between layers is achieved by hot-deformation method. The combination of high temperature and large plastic deformation would lead to severe microstructure evolution and break-up of the oxide films, which facilitates the full recovery of the joint performance to base level.For this new manufacturing method, the quality of the bonded interface and its dependence on the deformation condition would be the key focus. In this work, the effects of temperature on the bonding quality is investigated with IN718 samples using Gleeble. The tensile results of the bonded samples show comparable properties with the references.

This paper designed several routes of heat treatment and wire arc additive manufacturing (WAAM) based on a rolled aluminum alloy plate 2219 to study the effect of heat treatment on mechanical properties of hybrid materials which are formed by WAAM on the AA2219 base. The test results show that the average tensile strength of the aged hybrid materials based on an annealed aluminum alloy is significantly increased, but its average elongation is obviously reduced, compared to the specimens obtained by other heat treatment routes; and that the fracture locations of the hybrid materials are mostly in the WAAM region, which indicates that the strength of the WAAM region is smaller than that of the substrate region.

Press-hardening is an important metal sheet manufacturing process to improve the metal sheet properties during forming with an inline quenching process. This requires higher cooling rates often obtained by cooling channels within the tools, that enable the formation of martensite for a high strength. The manufacturing of those forming tools with internal cooling channels is quite complex, time and material consuming and therefore expensive. Optimal cooling channel geometry cannot be realized by conventional machining operations, that limits cooling efficiency too.Wire Arc Additive Manufacturing (WAAM) is a layer-wise welding process, that allows the manufacturing of near net shapes and internal cooling channels. In contrast to conventional machining, manufacturing of a complex lightweight design forming tool can be realized by WAAM. This will further reduce the WAAM process time and material consumption. However, the lightweight design reduces on one hand the thermal mass and thus the capability of heat transfer, making cooling via the cooling channels more crucial. On the other hand, elastic tool deformation has to be as low as possible.In this study, a press-hardening forming tool made of S235JR is designed and manufactured by means of WAAM. FEM analysis are performed to optimize the design of the forming tool regarding lightweight aspects. Simple near net shapes of cooling channels are considered for a simplification of the WAAM process. The forming tool is mechanically tested to compare and evaluate the stiffness with the FEM analysis.

The use of light alloys in automotive applications has been rapidly increasing in the industry as a means to reduce fuel consumption and carbon dioxide emissions. Semi-solid forming process for Al-Si based alloys, which produces near-net shape components with the desired properties and cost effectiveness satisfies the requirements in this regard. This paper explores the potential of Al-Si based alloys in semi-solid forming of truck components, which were originally casted in iron-based alloy. The Swirled Enthalpy Equilibration Device (SEED) technique was utilized to prepare semi-solid slurries of A356 and 319s. In order to improve the mechanical properties of rheo-HPDC components, various heat treatment cycles were studied. Microstructural characteristics of the alloys under different heat treatment conditions were examined using optical and scanning electron microscopy. Hardness and tensile experiments were applied to evaluate the mechanical properties of the alloys. A comparison of cost and static load performance was conducted for various materials. The findings indicate that the rheo-HPDC technique has been successful in producing Al-Si-based alloys with an optimal microstructure that combines both quality and mechanical performance.

In this study, the SiCf/Ti6Al4V composite was fabricated by hot isostatic pressing (HIP), in which the bundle polymer-derived (PD) fibers and powder titanium alloy matrix were employed. The effectiveness of the metal powder to be well infiltrated into the voids of the fiber bundles was explored and discussed. The microstructure of the fabricated composite was characterized by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The SEM observations show that the SiC fibers and titanium alloy matrix are well bonded through the interfacial layer that is uniform with a thickness of 1–2 μm. The EDS results show that the element mutual diffusion occurs at the interface, indicating that the bonding mechanism is a diffusion reaction. The matrix exhibits ductile characteristics, while the brittle characteristics appear in the reaction zone. The reinforcement mechanism is that the matrix will produce plastic deformation under the stress, thus transferring the load to the fibers to bear through the interface. It is concluded that the HIP is a suitable process to fabricate high-performance SiCf/Ti composites, which could facilitate the further fabrication of SiCf/Ti composites with a quasi-isotropic property for heat-resistant skin structures.

Diamond/Al-alloy composite, with its features of high thermal conductivity and low density, is one kind of recently developed lightweight heat dissipation material. In this paper, a novel method of semi-solid powder forming (SSPF), a fabrication method that exploits the unique behavior of a liquid-solid mixture, is used to fabricate the diamond/Al-alloy composite. The Al-alloy matrix is designed as a bi-metal system, including an Al-alloy powder with higher melting temperature acting as solid flexible skeleton to support the diamond, and another with lower melting temperature acting as liquid filler to fill pores between powder gaps. The density, electrical conductivity, thermal conductivity, and microstructure of the composites were studied. Results show that the interface wettability and plastic deformation are encouraged while the sintering temperature is increased from 753 K to 833 K, which helps to increase the relative density of the composite from 95.8% to 99.8%. Besides, the thermophysical properties of the composite are significantly influenced by the intrinsic conductivity of reinforcement and matrix. It is helpful to reduce the residual pores by deforming and sintering in a liquid-solid co-existent state during the SSPF process. Moreover, the densification mechanism is summarized as four stages: volume packed density reaching peak; alloy powder softening and deforming; alloy powder partial melting and filling into powder gap; cooling and densification.

The increasing focus on environmental issues in industrial production has resulted in various attempts to develop new, environmentally friendly tribology systems for metal forming in order to substitute hazardous lubricants such as chlorinated paraffin oils. The authors have been engaged in a framework program ‘SHETRIB - New environmentally benign sheet metal forming tribology systems’ in collaboration with Danish and Swedish industry. A number of new solutions are presented: (i) further development of a methodology for off-line testing of new, environmentally friendly lubricants, (ii) successful testing and introduction of new, environmentally benign lubricants in industry, (iii) development of a tool coating diminishing the risk of galling in sheet stamping and ironing of tribologically difficult workpiece materials such as stainless steel, and (iv) development of tailored tool surfaces enhancing micro-plastohydrodynamic lubrication in deep drawing and ironing. Different ways to detect the onset of galling are also presented including acoustic emission, a promising alternative for on-line production monitoring.

The warm and hot upsetting sliding test (WHUST) is a direct measuring method of friction coefficient in metal forming processes. This specific test can conduct severe contact conditions referring to the tool-workpiece interface. In the WHUST, a contactor slides along a specimen with a constant penetration depth to generate a plastic strain in the vicinity of the contact surface. When performing the WHUST on aluminum alloys at high temperatures, pile-up material occurs in front of the contactor, causing a modification of the contact geometry. This study aims to indicate the impact of the pile-up material on identifying the friction coefficient. The analytical equation to determine the friction coefficient is presented, which considers the parameter of the pile-up material. In this study, the WHUST was scaled down from the existing device [1] and installed in the hot chamber to perform the tribological test at a precisely controlled temperature. The experimental data were used to identify the friction coefficient by different equations with and without considering the parameter of the pile-up material. Comparing the results show that the friction coefficient can be overestimated if the pile-up material is avoided to consider in the equation. Moreover, the evolutions of the friction coefficient and the material transfer at different sliding distances were experimentally investigated in this study by the WHUST on AA 6082-T6 aluminum alloy at 400 ℃.

Over the last decades, the application of ultra-high strength steel (UHSS) has constantly increased within the automotive industry due to its favorable strength-to-weight ratio. In this regard, hot stamping is used to manufacture such steel grades to geometrical complex car body components with high shape accuracy. Hot stamped parts are commonly made out of boron-manganese steel sheets, which are initially austenitized and subsequently formed and quenched simultaneously. During forming, however, high thermo-mechanical tool stresses appear, which in turn promote the occurrence of severe wear and high friction at the blank-die interface. After short time production, the quality of the parts as well as the operating time of the tool is negatively affected. To counter this, an innovative surface engineering technology named laser implantation process has been investigated, in order to improve the tribological performance of hot stamping tools. Within prior studies, the effectiveness of this technology has already been proven in laboratory scale by means of modified pin-on-disk and quenching tests. However, the tribological impact under industrial-related contact pressure has not been analyzed so far. Furthermore, the transferability of this technology to a deep drawing process has not been investigated in detail. To counter this, hot strip drawing tests with surface pressures ≥ 20 MPa have been performed to evaluate the tribological behavior. Furthermore, a locally modified as well as a conventional die were utilized for hot stamping rectangular cups, in order to compare their tribological impact.

This is a report on research aimed at visualizing the punching state for detecting tool wear by analyzing the vibrations of the die.In this study, we examined the possibility of visualizing shear processing state by comparing surface of punching hole with corresponding vibration data.Vibration data during punching with non-wear and wear tools were obtained by using an accelerometer on the outside of the punching die. Load and displacement data were also recorded. The cut surface of each punch hole was observed with a scanning electron microscope. As a result of analyzing the cut surface and the corresponding vibration data, there was a correlation between the cut surface and the vibration data for both the non-wear tool and the wear tool. These results suggested the possibility of tool wear detection during punching by sensing the vibration of the die.

We developed a forced lubrication technology that supplies high-pressure lubricant between a die and a tube during hydroforming process (Japanese patent application number: 2021–143672). In this study, we performed experiments on time- and area-dependent forced lubrication during tube hydroforming based on this technology. We obtained the following findings about time-dependent lubrication: 1) The thickness distribution can be controlled by lowering the lubricant pressure during forming. 2) Increasing the internal pressure at which the lubricant pressure is lowered tended to reduce the thickness in the vicinity of the lubricant supply port (center of the flat area) and increase the thickness of corners. In other words, there was a trade-off between the thickness of flat areas and corners. 3) Controlling the lubricant from the start to the middle stage of forming is important in controlling the thickness distribution. We obtained the following finding about area-dependent lubrication: 4) Lubricant flow can be held back by providing a level difference of 0.1 mm–0.2 mm at a position 5 mm–15 mm from the lubricant supply port. Product surface quality is improved when the level difference is small. These time- and area-dependent forced lubrication technologies will contribute to improved design freedom of products such as automotive parts. They will also be effective in reducing process and product design rework because they allow product performance to be controlled using manufacturing parameters.

Brass foils have several desirable mechanical and physical properties. However, these brass foils are prone to corrosion and dezincification. Presence of a small amount of zinc in brass causes micro-cracks in high-pressure and corrosive environment. Surface modification through a protective coating is necessary to improve the corrosion resistance and mechanical properties of brass. In this regard, electroless Ni-B coating emerged as a promising surface coating process. Electroless coating benefits include homogenous deposition on an even/uneven surface, direct deposition on a catalytic surface, less porous structure, increased corrosion resistance, simple and cost-effective procedure. In the current study authors have developed a protective Ni-B coating through electroless deposition (ELD) process over a brass foil of 100 µm thickness. Since, brass substrates are not catalytically active, a nickel (Ni) layer was first deposited all over the brass foil through electroplating (ED) process to obtain a catalytically active surface. After that, Ni-B coating was deposited over the Ni layer using the ELD process. X-RD spectrum of ELD Ni-B coating showed a broad peak of Ni, indicating the presence of amorphous phases. Top surface morphology of developed ELD coating, shows uniform nodular grains and crack free surface. During heat treatment at 450 ℃ in air, the nodular grains grow in size. After heat treatment, several sharp peaks associated with a crystalline nickel and nickel boride phases (Ni2B and Ni3B) were detected. Ni-B coated Brass foil shows improvement in the hardness value (568 ± 50 HV0.1) as compared to brass foil.

This article contains interesting results from numerical modelling of forging tool wear. It concerns tools with hybrid layers combining hardfacing and nitriding. These are original layers that significantly improve tool life in hot forging processes, which is also confirmed by the results presented here. The authors developed their own wear model based on the Archard model. The new model takes into account the hardness of the material in the surface layer that is given by hardfacing and by nitriding. In addition, it takes into account changes in hardness as a result of exploitation in hot forging processes. The results of the tests confirmed the model's consistency with experiment at a level of 70–90%.

Gradual material loss due to wear causes geometrical deviations in tools and indirectly in part geometries in metal forming applications. Therefore, improvement of forming tool surfaces to prolong tool life is a constant challenge. Conventional hardness enhancement applications include generating a diffusion layer or PVD coating. A recent approach to further enhance surface hardness and increase the hardness depth of metal forming tools is to apply severe shot peening (SSP) prior to nitriding. Dislocation density increase combined with the ultra-fine grains generated after SSP on surface layer provides faster diffusion of nitrogen molecules. However, increase in surface roughness may be observed after SSP which may cause inhomogeneities in nitride layer. In the current study, effect of the initial surface roughness on the final surface topography of 1.2379 tool steel after SSP has been investigated. Three different surface states were generated using grinding, sandpapering and polishing. After hardening the samples to 61 HRC, SSP has been applied on specimens. Studies revealed that SSP decreases surface roughness for ground samples while increasing the same property for sandpapered and polished ones. Moreover, it is found that surface region hardness can be increased via SSP and subsurface microstructure can be altered. Such a modified microstructure may enable better nitride diffusion.

Deep Rolling as a well-known mechanical surface treatment process is investigated with the objective to tailor residual stress profiles over the sheet metal thickness. Experiments are performed in a milling portal on AA2024 aluminum alloy with a hydrostatically mounted deep rolling tool. Residual stress measurements are carried out using the hole drilling method. A numerical simulation using the finite element method (FEM) is set up and experimentally validated. One of the most effective parameters to tailor residual stresses is the deep rolling force, which is directly linked to the hydraulic tool pressure. The residual stress profiles can be described by characteristic values such as the magnitude of the maximum compressive residual stress and its penetration depth. Deep rolling modifies residual stresses not only along the material depth but also along other spatial directions.

Laser quenching process tests of 7CrSiMnMoV steel at different laser power and scanning speeds were carried out. The effects of laser quenching on the microstructure of the hardened layer and heat affected zone were investigated, and the influence of laser process parameters on the distribution of martensite, residual austenite, and grain size were obtained. The results indicated that a large amount of martensite was formed in the hardened layer after laser quenching, and surface strengthening was realized under the combined action of grain refinement, phase transformation strengthening and aging strengthening. The effect of laser process parameters on the hardness of heat-treated specimens was investigated and the relationship equation between the hardened layer depth and laser energy density was obtained. A finite element analysis model of laser quenching process of 7CrSiMnMoV steel was established based on ABAQUS software to realize the simulation of the temperature field during the laser quenching process. The process optimization based on the response surface method was carried out, when the laser power, scanning speed and spot size are 1493.9 W, 2 mm/s and 20 mm × 3.9 mm respectively, the hardened layer depth of 0.829 mm can be obtained.

Forging processes are defined by variables related to the workpiece, the tools, the machine, and the process itself, and these variables are called process variables. They have a direct impact on the quality of the finished product, so it is important to accurately define them at the very beginning of the process design. Nowadays, the design stage is supported by numerical simulations, however, these simulations are made under ideal process conditions and do not consider the dynamics of the forging machine or the variabilities that may occur in production (e.g., variabilities in the dimensions of the billet). This suggests that among the different process variables, those defined for piloting the process (such as the blows energies, for example) are fixed under nominal conditions and are not calibrated for each part produced.This study exploits a methodology in four steps to create a surrogate model and implement it into a machine-behavior model for real-time piloting of a forging operation with a screw press. This model supports the piloting of the operation, providing a value for the energy setpoint, according to the current state of process variables, these being the input of the model. The methodology is detailed for a multiple-blow cold upsetting of a copper billet.

This paper proposes a general forging die design with sequential forging press extension (GeneDieSFX) method, which is based on an extension of the general forging die design (GeneDie) method, for totally non-axisymmetric cold- and warm-forged products that can be deformed using the sequential forging press (SFP) method. The SFP method uses two punches located on the left and right sides of the upper and lower dies and shares the same dies while exchanging these punches in all forming stages. The basic die structure, which represents the relative positional interrelationships among the various components of the forging dies, is extended to support a new die structure for the SFP method. The forming surface configuration, which represents the correspondence between the functions allocated to the surfaces of the forging dies and the surfaces of the forged product, is also extended to distinguish the forming surfaces of the two punches that press the work material from the left and right sides. In addition, a die unification procedure is introduced to share the dies in all forming stages. An experimental knowledge base for die design support was developed and applied to process plans designed by an experienced engineer for forming of an electrical connector. The experimental results show that the proposed method can generate forging dies that are functionally comparable with dies designed by the experienced engineer.

Models using masses dampers and springs have been developed to represent the dynamic behavior of forging machines piloted by energy, like hammers or screw presses. But until now, most of these models are describing an entire production system including both the forging machine and its tools. Thus, if the same machine is used but with different tools, the entire model may be wrong and has to be completely redefined. This work proposes a first step toward the dissociation of the tools from the machine in the dynamic model of a screw press and its tools. Bare strikes, without billet, were performed on a screw press with two different tools configurations. The load and ram acceleration signals as well as their Fourier transforms were compared for the two different tools configurations. A two degree of freedom model is identified, with a first mode found to be press dependent and a second mode that is tool dependent. The masses, stiffnesses and dampers model’s parameters were identified for both tools configurations and largest deviation were observed for the second mode parameters. Thus, confirming the possibility to dissociate the press from the tools in the dynamic model.

The frequency distribution of local stress or strain across the micromechanical field in plastic deformation tends to universally follow a normal or lognormal distribution, regardless of the variety of microstructural inhomogeneity. However, it has not been reported how size effect (SE) influences the grain-scale statistical distribution of stress and strain in microforming, and thus an in-depth investigation is further needed. Taking the polycrystalline Cu sheets with thickness t = 0.1–1.5 mm and t/d = 1–29 as the case materials, this study implements the full-field CPFE simulation incorporated with a size-dependent dislocation-based constitutive model and statistical analyses to explore the influence of SE on the frequency distribution of grain-scale stress and strain in micro-scaled plastic deformation. With increasing t/d, the stress frequency consistently follows a normal distribution. In contrast, the frequency distributions of strain and dislocation density undergo a transformation from a lognormal distribution to an approximately normal distribution. The results indicate that the distribution law of stress is dominantly influenced by the dislocation density, while that of strain is determined by a multiplicative process of slip activities. The established knowledge will help to elucidate the nature of the distribution law of stress or strain, and to seek for effective approaches to alleviate the scatter and uncertainty of deformed part geometry during a microforming process.

Friction extrusion (FE) is a thermo-mechanical process using a rotating die or feedstock to produce fully consolidated extrudates in different shapes, e.g. wires, rods and tubes. FE utilizes a non-consumable die to plastically deform material and generate heat by friction due to the relative rotation between the die and feedstock, i.e. FE represents a more energy-efficient process compared to classical extrusion techniques. In this study, the FE process is applied to extrude the Al-Cu alloy AA2024 using a 90 degree scroll-featured die. The grain structure evolution induced by thermo-mechanical processing is analyzed, in particular using the electron backscatter diffraction technique. Introduction of severe plastic deformation and high-temperature exposure induced by the die movement in radial and longitudinal directions relative to the materials enable grain refinement induced by dynamic recrystallization. The grain structure formation prior to deformation through the die orifice plays an essential role to obtain fully recrystallized homogeneous wires.

Constraint uniaxial compression of magnesium single crystals along c-axis was carried out at room temperature and elevated temperatures of up to 500 ℃. The deformation structures were characterized by electron backscatter diffraction (EBSD). The results showed no evidence of pyramidal <c+a> slip and twinning was responsible for plastic deformation in the range of temperatures tested. The atomic configurations and crystallographic features associated with pyramidal <c+a> dislocations were revealed with the help of CrystalMaker software and a possible <c+a> dislocation core structures was reconstructed. The crystallographic analysis suggested that pyramidal slip was difficult because <c+a> dislocations would involve too many atoms on irrational lattice planes and directions.

Magnesium alloy has the superiority of low density, excellent machinability and admirable dimensional stability, however, cause by it has the closely-arranged hexagonal crystal structure, there are a small amount independent slip systems at room temperature, that means poor plastic deformation ability. This investigation revealed the plastic deformation and fracture characteristics of magnesium alloy sheets by procedures of crystal plasticity (CP) and in-situ SEM experiments. The influence of the occurrence of the second-phase particles, grain boundaries distribution on the grain boundary cracks and grain boundaries damage on the microstructure morphology was analyzed by the observation and simulation. Results demonstrate that the damage evolution regulation along grain boundary of ZK60 magnesium alloy was verified by using investigation during plastic deformation, and the generation and propagation of microcracks on grain boundaries showed little difference with the experiments results. The presence of the second-phase particles is more likely to motivate the initiation of cracks at the grain boundary, which enables it easily to originate grain boundary fracture, and the crack predominantly distributes at the junction of grain boundaries or multiple grain boundaries. The final overall fracture is both related to the influence of local large cracks and the damage accumulation of the whole fracture path. Regulating the local damage distribution is beneficial to coordinating the overall damage. This study deepens the understanding of intergranular fracture, mechanical response and microstructure evolution of ZK60 magnesium alloy sheets during tensile deformation at room temperature.

Grain boundaries (GBs) are the most vulnerable areas of metals during high temperature forming and processing where microcracks are highly likely to affect their macroscopic properties, resulting in fracture and ultimately reduced service life. In order to investigate the mechanisms of micro- and nano-scale damage evolution, microcrack initiation and propagation, GBs must be included as a crucial consideration in the theoretical and modelling solutions. Thus, to accurately illustrate the influence mechanisms of GBs on the mechanical behaviours, the cohesive zone model (CZM) considering GB damage evolution and the crystal plasticity finite element model (CPFEM) coupling slip and twinning inside the grain, were combined to propose a micromechanical mechanism of TWIP steels, which is applicable to predict the strengthening, damage and fracture of TWIP steels under high temperature. The CZM-CPFE method was confirmed by in situ SEM experiments at 750 ℃. The representative volume elements (RVEs) are constructed to predict the high temperature deformation behaviour of TWIP steels with different grain sizes and initial microdefects to obtain the influence of different initial states on the high temperature deformation behaviour, which can provide the solid theoretical basis for the subsequent manufacturing and forming processes of TWIP steel sheets. This work not only fills the gap in theoretical modelling of TWIP steels in the field of hot processing and manufacturing, but also provides some research approaches and analysis strategies for the GB damage behaviour of polycrystalline materials at high temperatures.

Due to their high specific strength, rolled Magnesium sheets have excellent prerequisites for lightweight construction applications. However, the hexagonal crystal structure of Mg offers only few slip systems that can be activated at low temperature, thus limiting the ductility. Additionally, the pronounced texture of rolled Mg sheets further limits its cold formability. Equal-Channel Angular Pressing (ECAP) is a suitable way to tailor the crystallographic texture, refine the grains, and thus improve the formability of the sheets. Since it is a discontinuous process, deformation can be applied in different shear planes by rotating the sheets. The influence of these so-called process routes on the resulting microstructure of the sheets is investigated in this work using a Mg-Zn-Y-Zr-RE alloy. Already after the second ECAP pass, a noticeable grain size refinement could be achieved. Furthermore, experimental studies showed that the elongation at fracture at elevated temperatures of the Mg alloy can be increased by ECAP.

The mechanical characteristics of CNTs/Al composites are widely reported to be reinforced by carbon nanotubes (CNTs), but intergranular and intragranular CNTs play different roles in strengthening, whose detailed effects are hard to be directly observed and are not fully clear. In this paper, the strengthening mechanisms of aluminum matrix composites (AMC) reinforced by CNTs at different positions (intragranular or intergranular) are explored on an atomic scale. Molecular dynamics (MD) simulation models for AMC reinforced by intragranular and intergranular CNTs are constructed. The uniaxial tensile deformation tests are carried out at the temperature of 300K, using periodic boundary conditions (PBCs) in all three directions. The results show that adding CNTs in the aluminum can significantly strengthen the mechanical properties of the AMC. The improvement in tensile strength of the CNTs-reinforced materials is respectively 29.7% and 25.4% when compared with defective single-crystal aluminum (SA) and double-crystal aluminum (DA). Moreover, the strengthening mechanism of AMC reinforced by intragranular and intergranular CNTs is further explored through the MD simulations, including dislocation density and lattice structure transformation.

α-Ti sheets are widely used in manufacturing miniaturized components for the outstanding specific strength, corrosion resistance, and formability. However, the size effect brings severe challenges to the deformation and the service of micro parts, and the plastic anisotropy of α-Ti makes the micro-forming process more complicated. Therefore, a series of in-situ experiments and full-field crystal plasticity simulations were carried out to investigate the coupling effect of geometric size and plastic anisotropy of α-Ti. Anisotropic size effect on the plastic deformation was observed, and Diagonal Direction (DD) specimen shows a higher size effect sensitivity than that of RD (rolling direction) and TD (transverse direction) specimens. The flow stress and fracture strain decrease as the geometric size decreases, and the DD specimen shows a higher fracture strain reduction. Evident surface roughing and a higher proportion of hard-oriented grains in DD4 results in stronger intergranular strain heterogeneity, which leads to the formation of through-thickness shear bands as the geometric size decreases. The fracture mechanism in α-Ti transforms from a micro-void coalescence ductile mode to a brittle one as the geometric size decreases. These findings provide a fundamental understanding of the anisotropic size effect on the tensile behavior of α-Ti.

Ti2AlNb-based alloy has great application potential in the aerospace industry due to its low density, high service temperature, and excellent mechanical properties. However, the ingots of this material are usually composed of coarse grains, even up to centimeter grade, which should be refined by deformation to avoid the deterioration of their workability and in-service performance. In this work, the grain refinement mechanism of as-cast Ti2AlNb-based alloy was investigated by uni- and multi-axial compressions at elevated temperatures. The results of uniaxial compression demonstrated that the grains were significantly elongated without volume change, indicating little recrystallization even after very large deformation. The investigation showed that the dislocations induced by deformation were prone to annihilate via dynamic recovery, while dynamic recrystallization (DRX) was inhibited due to insufficient dislocations. Two multi-axial compression schemes were compared, i.e., two-step compression with 60% reduction per step (Scheme 1) and three-step compression with 40% reduction per step (Scheme 2). The results indicated that the recrystallization fraction of deformed samples in Scheme 1 was much higher than that in Scheme 2, although the total strain of those two cases was similar. It is concluded that the formation of dislocation substructures in the former deformation, which strongly affects the intragranular misorientation, is the key factor to trigger the recrystallization in the processes followed.

The challenge implementing magnesium sheets as a lightweight material is to manufacture sheets with an acceptable formability at room temperature and sheet components with a suitable strength. The aim of this work is qualifying suitable alloys and their manufacturing process in a way that precipitation hardening is enabled after the final forming process. The precipitation morphology and the rapid solidification obtained by twin roll casting process are used to find an optimum microstructure for deep drawing and to increase the strength of the formed component by heat treatment.The results show that magnesium sheets made from Mg-Zn-Al-Ca exhibit good forming properties even after rolling from the slab, as well as an increase in hardness after a suitable heat treatment. The production route of sheets via twin roll casting process exhibits higher increases in both ductility of the sheets and hardness after heat treatment compared to the production route via ingot-rolling. This paper presents results of rolling experiments with different feedstock of Mg-Zn-Al-Ca alloys, the microstructures and textures, as well as their mechanical properties and Erichsen values. In addition, various heat treatments were carried out to increase hardness. The second part of the paper deals with the development of a suitable heated deep-drawing tool and shows the heat distribution in the tool as well as first results of the deep-drawing tests.

Non-grain-oriented (NO) electrical steels are soft magnetic materials that are commonly used in electrical drives and machines. The magnetic properties of NO electrical steels are influenced by the alloying components (Si + Al), sheet thickness, grain size, and crystallographic texture. Compared to the conventional production of NO electrical steel sheets, which includes continuous casting, hot and cold rolling as well as final annealing, the strip casting process route represents a promising alternative. In addition to a shortened process chain and the associated energy savings and emission reductions, the process also shows a potentially positive influence on the crystallographic texture of the semi-finished sheet. In this work, microstructure and texture evolution during warm rolling of NO electrical sheet with Fe-3.5Si-2Al alloy produced via strip casting is investigated. The experimental investigations involve texture and microstructure measurements before and after rolling. A multiscale top-down simulation model was developed for texture prediction during rolling. The model consists of an elastic plastic-based FEM simulation of the warm rolling process, from which the history of the deformation gradient at different locations for the sheet in the roll gap is obtained. This variable is then imposed on a representative volume element developed with the experimental measurements. Their evolution is simulated with the DAMASK crystal plasticity tool. Here, based on the experimental flow curves, a physics-based dislocation density material model is calibrated by deactivating and activating the shear band parameters. Simulations are performed and the results of the texture evolution using the two models are compared with the experiments. The dislocation density model, when combined with shear band parameters, is best suited to accurately predict the texture intensities along the important λ-, α- and γ-fibers for this material and the intensities quantitatively match the experimental results.

The present work aims to illustrate a methodology using the finite element FORGE® software for macroscopic forging simulations and then coupled with the finite element DIGIMU® software integrated metallurgical models with a full-field approach for simulating the microstructure evolution during the forging processes of 3 industrial components of Inconel 718. The metallurgical models in the DIGIMU® software include dynamic and post-dynamic recrystallization as well as the interaction of the matrix and the precipitates or the second-phase particles. The recrystallization model parameters were identified on forged laboratory samples. It was found that the developed models in the DIGIMU® software successfully predict both homogeneous and heterogeneous microstructures in terms of the average and the distribution of grain sizes on different industrial parts forged at super-solvus or sub-solvus temperatures. The findings demonstrate great potential of the DIGIMU® software in microstructure predictions, which can help optimize the forging processes.

The mechanical properties of high strength steel are governed by its microstructure, which typically exhibits a multi-phase composition when the steel is highly strong and ductile. The distribution, proportion, and morphology of the constituent phases significantly influence the final mechanical properties of the material. In this regard, the development of an accurate and efficient method to identify and segment the microstructure of high strength steel is essential. To address this issue, a microscopic image database of high strength steel materials was established and an unsupervised image segmentation method that leverages superpixels and texture features clustering was proposed to identify the complex microstructure of high strength steel. By optimizing the number of superpixel divisions, our method achieved high accuracy in segmenting the three types of mixed structures in the dataset, with average pixel accuracy scores of 79.21% (M + B), 86.23% (F + P), and 84.32% (F + A). Furthermore, our method outperformed traditional unsupervised segmentation methods in segmenting microstructure images with intricate textures. The proposed method is thus deemed an effective tool for studying and applying high strength steel materials.

Microstructural modelling offers the possibility of reducing the experimental effort and accelerating development processes. Here, full-field models are of increasing interest as they give an improved physical representation of the metallurgical mechanisms as well as a wider range of validity compared to simpler models. However, to be able to model microstructural evolution properly using a full-field model, the basic mechanisms of grain growth and recrystallization (RX) need to be characterized experimentally before identifying the model parameters. An important mechanism here is the post-dynamic recrystallization (PDRX), i.e., the evolution of microstructure after deformation at upheld elevated temperatures. Different characterization approaches like the stress relaxation method, interrupted compression or torsion tests have been used for PDRX investigations. However, no investigation on the influence of the different characterization methods on the final material parameters have been conducted. In this study, two characterization methods are used to investigate the PDRX of Inconel 718 in the commercial software DIGIMU®. Firstly, stress relaxation tests are conducted in the super-solvus area. Here a strain is applied before the onset of dynamic recrystallization (DRX) and kept constant during the test. The RX-kinetic is derived from interrupted samples during the holding time. Based on the RX-kinetics, a first set of model parameters is identified. Secondly, compression tests are interrupted at different DRX-fractions and subsequently held at the test temperatures to analyze further development in the post-dynamic regime. The previously identified parameters are used to simulate the microstructural evolution for the second set of experiments. Results show good agreement of the RX-kinetics in both cases. Deviations in the average grain size are identified for the interrupted compression test at 1120 ℃ while a very good agreement is reached for 1020 ℃ and 1070 ℃. The results suggest that it is possible to identify the PDRX parameters based on a testing method consisting of SRX and use them for MDRX simulations.

In real industrial process for metallic materials, complex stress states are usually involved with variations in texture features. Especially for Mg, Zr, Ti alloys with diverse slip systems and twinning modes, their texture evolution behavior are still unclear owing to the insufficient understanding of the relation between complex stress state and activation of plastic mode. In this paper, the effective Schmid factor (ESF) recently proposed by us is used to clarify the correlation among stress state, plastic mechanism, and texture evolution. With ESF calculation, the contribution of each stress component in complex stress state is reasonably considered with special good description ability for shear stress. Firstly, the intrinsic reason for the texture weakness for magnesium alloy sheet during differential speed rolling (DSR) are clarified with ESF calculation. It indicates that the shear deformation induced during DSR can change the stable position of basal <a> slip, and thus result in tilted basal texture. Besides, high activity of contraction twinning and pyramidal <c + a> slip can promote the dynamic recrystallization and further weaken the basal texture.

As a superalloy, Ti2AlNb-based alloy faces a great challenge due to the commonly existent centimeter-level coarse grains in as-cast material, which severely deteriorate their mechanical property. In-depth understanding of plastic deformation heterogeneity at grain-level of this material is pivotal in exploring the nucleation mechanism of recrystallization. In-situ plane compression tests combined with surface slip line observation and microstructure tracing were carried out on samples with centimeter-grade coarse grains. The results showed that the plastic deformation was heterogeneous in the samples, and the grain boundaries had little effect on hindering dislocation movement. Macroscopic shear direction significantly influenced the distribution of slip lines. Slip can be transferred from one grain to the neighbor grains through the grain boundary without changing the direction. Surface slip trace analysis showed that only a few slip systems were activated in grains. The activated slip systems in grains were affected by the orientation of the surrounding grains. The high deformation stored energy was formed at the band structure and the grain boundaries, and these regions can further occur recrystallization by aid of the heat effect.

The present article details the results obtained with recrystallization models based upon mean-field or full-field assumptions, respectively. The two models propose to simulate continuous dynamic and metadynamic recrystallization by explicitly describing the progressive formation and evolution of substructure. These two models are applied to simulate zircaloy-4 recrystallization. To identify model parameters and evaluate the model abilities and limitations, the numerical results are compared to experimental ones obtained from EBSD characterization on samples that have been submitted to hot compression or hot extrusion.

In the last ten years, full-field microstructural simulations have proven to be a very interesting tool to better understand and predict grain size evolution during industrial forming processes and heat treatments. Among the different solutions proposed in the literature, DIGIMU®, based on a level-set (LS) approach, has managed to gather several physical modules such as grain growth based on capillarity, dynamic, post-dynamic and static discontinuous recrystallization (ReX), as well as Smith-Zener pinning on second phase particles. This has permitted to carry out several accurate studies on nickel-based superalloys, austenitic stainless steels, and steels in the austenitic domain. However, until now, it was not possible to simulate the evolution of the precipitation state during the grain boundary (GB) network migration, and the ReX modeling was adapted to low stacking fault energy materials for which discontinuous nucleation events are predominant. This article illustrates very recent developments to simulate phenomenologically the second phase particles evolution. Two distinct populations can be considered, tracked by dedicated level-set functions, each one having its own evolution law. Furthermore, the development of the first full-field continuous dynamic recrystallization LS model, adapted to high stacking fault energy materials, is detailed. Applications on these new developments for nickel and zirconium alloys are presented and analyzed. Those two major developments enable DIGIMU® solution to go even deeper in the physics, to address accurately new materials presenting continuous dynamic recrystallization such as aluminum alloys, and new processes with temperatures close to the precipitates solvus.

For decades, numerous numerical methods have been developed to simulate microstructure evolution during hot metal forming. Two main families of methods exist, the front-capturing and the front-tracking ones, with both their strengths and weaknesses. In this work, we will consider a recent front-tracking method, inspired by the Vertex method, called ToRealMotion, developed some years ago. Contrarily to the Vertex method, in ToRealMotion, classical finite element (FE) mesh discretization is considered even in the bulk of grains in order to take into account also intragranular attributes and mechanisms, such as stored energy due to plastic deformation, solid/solid phase transformation, etc...In this work, an improvement of the 2D implementation of this method has been performed and has led to an important reduction in computational times and memory usage with an equivalent accuracy. Most of the optimizations have been performed on the data structure and the computation of the interface interpolation.

This study is devoted to the influence of shell material on microstructure and mechanical properties of twin-roll cast aluminum alloy of the Al-Si-Mg system. The use of high solidification rates during twin-roll casting can improve the mechanical performance of these alloys. The study involves two pairs of shells, made of hot work tool steel and high-strength copper alloy, and an age-hardening casting aluminum alloy. The solidification conditions are varied by using two different shell materials. The results show that the copper shells had a positive influence on the mechanical performance of the age-hardening casting aluminum alloy. It is demonstrated that the copper shells increased the solidification rate, resulting in a smaller dendrite arm spacing and improved mechanical properties, especially in regard to significantly improved ductility. The steel shells, on the other hand, showed lower solidification rates, resulting in larger dendrite arm spacings and inferior mechanical properties. Additionally, the twin-roll cast material is subjected to heat treatment including solution annealing, water quenching and artificial aging. After the heat treatment characteristics of mechanical properties are distinctly improved. The study also provides insight into the correlation between microstructure parameters and the solidification rate based on microstructure analysis, which is crucial when comparing different tool materials.

Due to rapid advances in computational power, various numerical methods have become feasible for simulating complex microstructure evolution including recrystallization, among which Monte Carlo (MC), cellular automaton (CA), and phase-field (PF) methods are the most commonly used in the mesoscale. Here, a PF model was established to predict the microstructure evolution during both dynamic recrystallization (DRX) and static recrystallization (SRX), which bear certain similarities in the nucleation and grain growth processes. Traditional algorithms solving the PF model usually assign each grain a unique phase-field variable to avoid grain coalescence, making the simulations computationally expensive especially when a large number of grains are present. Therefore, an efficient grain remapping algorithm was incorporated into the present PF model to accelerate the simulations, which allowed multiple grains to share the same variable and thus greatly cut down the number of variables required. Microstructure evolution during SRX and DRX was simulated, and it suggested that the algorithm yielded faithful results of the original model, and significantly reduced the computational costs.

Ni-based superalloys are critical materials of aero-engine turbine disks and blades. Microstructure characterization of Ni-based superalloys during thermal exposure have been investigated in present research. The evolution characteristics of grains, γ′ phase and twin boundaries of Ni-based superalloys during thermal exposure at 650 ℃ for 10–5000 h were analyzed based on OM, SEM and EBSD. The results show that crystal boundaries bending when thermal exposure time reaches 5000 h, the grains size un-occurred significantly variation, Σ3 twin boundaries first increase and then decrease. The morphology of secondary γ′ phases changed from initial near spherical / square to spherical, the size increase and content decrease with thermal exposure time prolongation. Tertiary spherical γ′ precipitates priority growth and precipitate as spheroids and ellipses, and content decreased significantly during thermal exposure for 2000 h. Microstructure characterization of Ni-based superalloys during near-service status have been revealed in present research, which provides theoretical reference for service conditions of Ni-based superalloys.

Since 25 years, the front-capturing level-set method has demonstrated its potential for the simulation, at the mesoscopic scale, of numerous mechanisms in the context of microstructure evolutions occuring during complex thermomechanical paths encounter in hot metal forming processes. This proceeding illustrates recent developments concerning the level-set method applied to this topic.

The predominant crystallographic relations between dynamic recrystallization (DRX) nuclei and simple deformation structures have been characterized in aluminum single crystals (ASCs) of Cube{001} < 100 > and S{123} < 634 > orientations. The ASCs were uniaxial compression at different temperatures (25, 300 ℃) and strain rates (0.001, 10 s−1). The deformed ASCs were analyzed using electron backscattered diffraction (EBSD) and electron channeling contrast imaging (ECCI). Local orientation measurements implied that Cube-oriented ASCs are dominated by a group of microbands, while DRXs in S-oriented ASCs are significant. There are few discontinuous dynamic recrystallized (DDRX) grains in Cube-oriented ASCs, while DDRX grains in S-oriented ASC reach a millimeter level at 25 ℃/10 s−1. Many continuous dynamic recrystallized (CDRX) grains and sub-grain structures are observed in S-oriented ASCs at 300 ℃/10 s−1. Misorientation angles across the DRX interfaces are grouped in the range of 20–50° (with a maximum at 30–40°). The diverse distribution of slip systems and stress-axis orientations in differently oriented ASCs contributes to the difference in the initial slip system, misorientation accumulation and DRX behavior.

Mg-Zn alloys with Ca and Sr additions were prepared by vacuum melting and hot extrusion. Effects of Ca or/and Sr on microstructure, mechanical properties of hot extruded Mg-2Zn-xCa-ySr (x = 0, 1) were studied. The results show that Ca addition into Mg-2Zn alloys significantly refine grains of Mg-2Zn alloys, while Sr addition greatly improves homogeneity of the grain structure. Fine and homogeneous microstructure is obtained by compound addition of Ca and Sr into Mg-2Zn alloy. With Ca and Sr addition, the best comprehensive mechanical properties are obtained in Mg-2Zn-1Ca-1Sr alloy with ultimate tensile strength of 308 MPa and elongation of 19%.

The complicated and coupled effects between dislocation and dynamic recrystallization inducing deformation inhomogeneity and further damage in the hot plastic deformation process of 7075 aluminum alloy restrict the formability of thin-wall parts for new energy vehicles. In this paper, the influence of grain size on hot deformation inhomogeneity of 7075 aluminum alloy under uniaxial tension is investigated. Then, a multiscale dislocation density based crystal plasticity model is established by considering dislocation slip. After verification, the virtual polycrystalline RVE models with different grain sizes and representative crystal orientations were constructed and embedded into crystal plasticity simulation in DAMASK via spectral method. The simulation results show that with the increase of grain size, the von Mises stress and dislocation density decreases. By introducing a proportion of Cube, Goss and other recrystallization texture, the von Mises stress is 8 MPa lower than that of random crystal orientation at the same grain size.

In this paper, the Ferrite-Ferrite bi-crystal model constructed based on Coincidence Site Lattice (CSL) theory has been simulated by Crystal Plasticity Finite Element Method (CPFEM) under three stress states, namely uniaxial tensile, shear and plane strain, and the correlation of grain boundary deformation coordination with slip transfer coefficient and stress state was analyzed. The results show that both stress state and grain orientation affect the deformation uniformity in the grain boundary region. For the coincident bi-crystal model, the slip transfer coefficient is 1, and the deformation of the interface region is uniform. For hard grains, the deformation coordination behavior can be predicted by the slip transfer coefficients between the four activated slip systems on both sides, while for soft grains, the grain boundary deformation is uniform and independent of the slip transfer coefficients.

In this study, we investigated the effect of multi-directional forging on the microstructure and mechanical properties of 20vol.% SiCw/6061Al composites. The results showed that the strength of forged workpiece did not decrease with the decrease of the whisker length. The improvement in the strength and fracture to elongation of multi-directional forged workpiece originated from the effective elimination of casting microstructural defects by the plastic deformation. In the free forged workpiece with an incremental pass strain, the average equivalent strain is smaller, and the strain distribution is more homogeneous with respect to that in the die-constrained forged workpiece with the same cumulative nominal strain. The heterogeneity in the hardness of die-constrained forged workpiece was mainly caused by the inhomogeneity of strain distribution. Besides, the multi-directional forging process with an increasing pass strain exhibits a bigger potential to improve the plasticity and homogeneity, and to decrease the anisotropy of forged workpiece.

Aiming at the grain size uniformity of TA15 titanium alloy unequal thickness thin-walled shell during hot forming, the hot drawing process of TA15 titanium alloy unequal thickness thin-walled shell is simulated by the DEFORM-3D software platform. Based on the grain size evolution model of equiaxed α in TA15 titanium alloy, the microstructure distribution and possible defects are researched. Then the influence laws of process parameters, die structure parameters and blank structure parameters on the uniformity of grain size are revealed, and the reasonable die loading speed and blank size are determined. Through orthogonal experimental analysis, the significance of the parameters affecting the grain size distribution uniformity of TA15 unequal thickness thin-walled shell is determined. The quantitative relationship model between die structure parameters and grain size distribution uniformity is established by using response surface method, and the reasonable combination of parameters to meet the requirements of grain size distribution uniformity is determined. The results could provide guidance for the intergraded manufacturing in forming and modification of TA15 titanium alloy unequal thickness thin-walled shell.

The hot workability of titanium alloy ingot is closely related to the morphology and size of initial grains. Based on the Gleeble thermal simulation experiment, the hot deformation behavior of equiaxed and columnar grains of Ti-6554 alloy ingot at deformation temperature of 950–1050 ℃ and strain rate of 0.01–1 s−1 was studied. The flow stress decreases with the increase of temperature or the decrease of strain rate. The strain modified Arrhenius constitutive model of equiaxed and columnar crystalline alloys was established by linear regression and polynomial fitting methods. And the predicted results were in good agreement with the experimental values. The results of microstructure evolution show that the density of grain boundary in unit volume of columnar crystal sample is higher. And the flow stress is greater than that of equiaxed crystal sample under the same deformation condition. With the increase of deformation temperature and the decrease of strain rate, the columnar crystal samples are more prone to DRX (dynamic recrystallization) than the equiaxed crystal samples. The equiaxed grains are transformed from serrated grain boundaries to bulged grain boundaries and regenerated into DRX grains. The columnar grains expands into a larger area of DRX region based on DRX strips or bulged grain boundaries.

To study metadynamic recrystallization, hot compression tests were conducted using Thermecmastor-Z thermomechanical simulator equipped with an automatic water-cooling system, which can shorten the delay time between the compression and cooling processes. The widely used offset yield stress method is no longer applicable to calculate the recrystallized fraction from the obtained stress–strain curve when the initial microstructure is as-extruded, because deformation in the two passes actually starts at different microstructures. A modified method to compensate for microstructural changes using the Hall–Petch relationship is thus proposed. Electron backscatter diffraction (EBSD) characterization and microhardness tests were carried out to get microstructural and mechanical properties for further understanding metadynamic recrystallization. During the interpass time, the external stress caused by the fixed anvil shows a non-negligible effect on the static softening behavior. It accelerates static recovery, but retards metadynamic recrystallization. As-extruded initial microstructure leads to a more recrystallized but less homogeneous microstructure and a smaller decrease in yield stress, showing good potential to maintain strength. Interestingly, unless the temperature or strain rate is sufficiently high, a certain incubation time, although as short as approximately 1 s, is still required for metadynamic recrystallization. In addition, not only the previously dynamic recrystallized grains, but also the recovery-enhanced subgrains, together act as potential nuclei for the subsequent metadynamic recrystallization.

Metal composites have attracted many interests due to their multi-functionality and excellent overall performance. Medium Mn steels have received much attention as the third-generation high strength steels owing to the good balance between the low material cost and the excellent anti-wear and mechanical properties. Low carbon steels can provide required mechanical properties as base materials at a relatively low cost. In this study, microstructure and mechanical properties of low carbon steel (SS400) and medium manganese steel (Mn8) were performed to evaluate the influence of annealing on Mn8/SS400 bimetal composite. The tensile strength and hardness of SS400 steel decrease, and the ductility of SS400 steel is improved with the increase of annealing temperature, which is attributed to the decreased density of dislocation. In addition, the hardness of Mn8 steel increases after annealing process caused by the phase transformation and grain boundary strengthening. Charpy impact tests of Mn8/SS400 bimetal composite were conducted to investigate the effect of annealing on the toughness at room temperature. The Charpy impact energies slowly drop with the increasing annealing temperatures, which presents the deteriorated toughness of Mn8/SS400 bimetal composite due to the decreased HAGBs and phase transformation.

In the present study, GH4175 superalloy was treated in the solution temperature range of 1100 ℃–1160 ℃ for 2 h, followed by unified aging treatment at 760 ℃ for 20 h. The microstructure of one step (only solution) and two-step (solution and age) treatment was compared to analyze the change of microstructure characteristics at different solution temperatures. The specimens after two-step treatment were subjected to tensile tests at 750 ℃, and corresponding fracture morphologies were observed to reveal the fracture behavior of GH4175 superalloy. The results show that the grain size of γ matrix increases from 4.6 μm to 6.8 μm as solution temperature increases from 1100 ℃ to 1140 ℃, but the volume fraction of primary γ´ particles decreases from 18.7% to 7.2%. The grain size of γ matrix significantly coarsens to 78.8 μm after solution treatment at 1160 ℃ because the dissolution of primary γ´ particles weakens the pinning effect. The secondary γ´ particles are refined after two-step treatment. An optimal yield strength of 1166 MPa is obtained by solution treatment at 1140 ℃ for 2 h followed by aging at 760 ℃ for 20 h. The re-precipitated secondary γ´ particles of GH4175 provide the major strengthening effect. However, as the solution temperature increases to 1160 ℃, the yield strength and elongation decrease to 1049 MPa and 2.88% respectively, which is attributed to the combined brittle intergranular fracture effect of coarsen γ grains and the distribution of undissolved carbides.

The metal additive manufacturing (MAM) process mainly derived from the metal welding process has unique advantages for the die manufacturing and repairing. To obtain the part with fine microstructure, and improve the performance of the complex die structure, the laser powder bed fusion (L-PBF) additive manufacturing process of Inconel 718 has been studied. A model combining finite volume method (FVM) and cellular automata (CA) method was used to explore the feasibility of simulating microstructure growth during the laser melt pool solidification from 2D to 3D. The process parameters of the multi-scale and multi-dimensional simulation were: 200 W (laser power), 1200 mm/s (scanning speed), 90 μm (hatch distance), and 30μm (layer thickness). The simulation result was compared with the experimental result of the same process parameters, and the feasibility of the model was proved. This multi-scale model can provide theoretical guidance for similar processes with focused energy sources and large temperature gradient solidification processes during die forming and repairing in the future.

This article describes a simplified 3D thermo-mechanical coupled finite element modeling approach developed to simulate geometric distortions in large bearing rings induced by manufacturing processes such as machining and heat treatment. Excessive distortions in the product may require increased stock conditions and extra machining steps and time, and therefore increase the material and manufacturing costs. The present modeling approach is focused on studying the geometric distortions induced by macro-scale residual stresses. To prevent the machining and material characteristics in the localized cut area from becoming dominating factors that make modeling challengingly complex and the simulation extremely expensive, simplifications and assumptions in the models are made. This simulation has been applied to several large bearing rings in production, and the distortion patterns correlate well with the actual products. The simulation results are also used to support decision-making in the selection of the various manufacturing processes.

Roll-bonded steel-aluminum laminates have broad application prospects. Intermetallic compounds (IMCs) are precipitated phases produced at bonding interface during annealing. Generally, IMCs are assumed to reduce the bonding strength of steel–aluminum laminates. In this study, we characterize that the IMCs formed at the initial stage of annealing do not reduce the bonding strength of laminates, and they can be used as a reinforcing phase at the interface to improve the bonding strength of steel–aluminum laminates further. In-situ tensile-shear test and finite element analysis reveal the changes in interfacial fracture form and stress–strain state before and after the IMCs formation. Results show that after the formation of granular IMCs at the interface, granular IMCs can limit interface crack propagation and change the crack propagation direction during tensile shear fracture, and the maximum shear stress at the interface is transferred from the interface to the aluminum substrate. Furthermore, the fracture of laminates occurs completely on the aluminum substrate. This state is damaged when the density of the interface IMCs is extremely high. After an approximate IMCs layer is formed at the bonding interface, Kirkendall voids are observed at IMCs–aluminum interface. During tensile shear, the maximum shear stress appears at the IMCs–aluminum interface, Kirkendal voids become the crack source and propagate rapidly, and the bonding strength of the laminates decreases.

In times of energy scarcity and global warming, simple but efficient smart processes are needed to reduce the need for natural resources and the production of climate changing gases. Therefore, ultrasonic vibrations in deformation processes could be a possibility because ultrasonic vibrations can reduce the flow stresses, decrease friction, increase the forming limit, produce heat, and increase the process efficiency of metallic materials, but until today the mechanism and the influences are not well understood, especially not for steels. The common ferritic-pearlitic C15E and austenitic X6CrNiMoTi17-12-2 steels are investigated in compression tests with additional different ultrasonic vibration amplitudes and durations in view of residual effects. Both steels showed residual softening after ultrasonic vibrations depending on the ultrasonic vibration duration and the ultrasonic vibration amplitude. The austenite showed a higher sensitivity to the ultrasonic vibration in terms of a higher residual softening and a higher temperature increase. Based on the mean flow stress, the temperature increase, the strain hardening rate, and the strain hardening exponent are discussed in the context of dislocation reactions.

A 2D MultiParticle Finite Element Model (MPFEM) was used to analyze the compaction by shot-peening of a multiparticulate coating. A representative microstructure was created from SEM cross-section observations of the coating and implemented into a finite element code. A first single shot study enabled the study of the influence of the process parameters (shot velocity, diameter, angle). The results were then used to simulate a multi-shot model, where the influence of the coverage was studied with the analysis of the change in morphology of the particles, the intraparticle plastic strain and the residual stresses in the coating. Simulations showed that: the velocity of the shot is the most influential parameter; the equivalent plastic strain has its maximum at the surface of the coating and increases with the coverage as well as the maximum compression. The compaction mechanisms are mainly the closing of interstitial pores and the elongation of the particles by plastic strain.

Due to their high specific strength and specific energy absorption capabilities, fiber-reinforced thermoplastics (FRP) have proven their potential and are used for lightweight design in many structural applications, especially in the automotive sector. Finite element simulations play an indispensable role in the design and optimization of structures. The behavior of composite materials under crash conditions poses challenges for simulations since it requires modeling beyond the elastic region and into failure initiation and propagation. Therefore, a methodology using the MAT54 material model in LS-DYNA was developed to design and validate the FRP structures for crash loadings.

The CNTs/Al is a promising lightweight high-strength composite in the aerospace industry. However, poor plasticity under room temperature limits its application. Eelectrically-assisted (EA) forming is expected to improve its plasticity by the Joule heating effect and athermal effect. In this study, the effect of electroplasticity on CNTs/Al with extrusion and T6 tempers is studied. It is found that for the specimen in extrusion temper, the flow stress under EA tensile condition is lower than that under warm tensile condition due to the promoted dislocation annihilation and dynamic recovery. For the specimen in T6 temper, the flow stress under EA tensile condition is larger than that under warm tensile condition, which is opposite to that in extrusion temper and is attributed to the formation of brittle phase Al4C3 and the evolution of grain and precipitate.

For warm drawing of twilled CFRTP(Carbon Fiber Reinforced Thermo Plastic), it is necessary to better predict wrinkling during deformation or bending and unbending at the corner of die and punch. Therefore, it is proposed to use a material model based on the change of crossing angle of twilled carbon fibers (in the following, the angle between the warp and the weft is called the crossing angle). In order to clarify the effect of this crossing angle, we prepared test pieces with different crossing angles by warm shear deformation, and measured the deformation resistance against loads in the direction in which the deformation progressed as well as in the reverse direction by tensile tests. From the experimental results, it was found that the increment of the deformation resistance when the deformation direction is reversed differs depending on the crossing angle. It was also clarified that the increment of the deformation resistance in the reversing direction becomes a larger value as the rocking angle, which is the limit crossing angle for deformation, is approached.

In this work, Csf/Mg composites are fabricated using a liquid-solid extrusion following vacuum pressure infiltration technique, and the elasto-plastic responses of the composites are then tested. Experimental tests are time and cost inefficient, and the two-step Mean-Field homogenization (MFH) method with the tangent formation is thus developed to predict the elasto-plastic responses of the composites efficiently. In the proposed method, an RVE of the composites is decomposed into a series of peuso-grains based on fiber orientation, and the Mori-Tanaka (MT) model with the tangent formation is used to predict the elasto-plastic response of each peuso-grain, following by averaging the elasto-plastic responses of all the peuso-grains using the Voigt model. Consequently, the two-step MT/Voigt MFH model is established to predict the elasto-plastic responses of the composites. Compared with the experimental tests and the FE homogenization method, the two-step MFH method and the related model are validated to be capable of efficiently predicting the elasto-plastic responses of the composites.

The ultra-large high-precision reflector panel is technical bottlenecks in construction of large-scale compact antenna test rang (CATR). To solve the problem, a negative pressure forming process was proposed to manufacture reflector panels with the sandwich structure based on reconfigurable discrete mold. Firstly, the deformation behaviours of each sheet at forming stage and sandwich structure at the springback stage were analyzed, and then, their mechanical model was established. Secondly, the technical factors affecting forming accuracy were researched, such as segmenting criterion, stress release, springback prediction and compensation. The control curve of segmenting ultra-large reflector surface was established. The process of releasing stress by slotting was developed. The finite element model of springback prediction was established to accurately predict forming precision. The process of negative pressure forming has been successfully used in the construction of an ultra-large CATR with 12 m quiet zone. The shape accuracy of a single reflector panel with area 6.4 square meters reached 0.03 mm (RMS), and the average forming accuracy of 30 panels was 0.034 mm (RMS). The final shape accuracy of the whole reflector with area 368 square meters reached 0.054 mm through on-site installation and alignment.