Proceedings of the First International Conference on Theoretical, Applied and Experimental Mechanics

Synthetically prepared metastable calcium carbonates (CaCO₃) polymorphs, vaterite and aragonite, were used for nanoindentation testing. Nanomechanical measurements were done on samples embedded in epoxy resins. Hardness and reduced modulus were determined and both values were found to be higher for vaterite. Hardness was determined to be in the ranges 1.1 to 0.2 and 0.5 to 0.1 GPa for vaterite and aragonite, respectively. Reduced modulus was found to be in the ranges 32 to 5 and 18 to 4 GPa, for vaterite and aragonite, respectively. Reduced modulus of vaterite was found to be approximately three times lower in comparison with vaterite sample prepared as pressed pellets. These results may be helpful for designing new products containing CaCO₃ for applications.

Growing crystals of soluble salts could cause degradation of porous building materials due to generation of crystallization pressure inducing tensile stress inside porous system. Considerable damage potential has been observed in case of sodium sulfate through phase change and rapid formation of hydrated phase mirabilite from highly supersaturated solution rising from dissolution of anhydrous phase thenardite after changing of surrounding conditions. Crystallization of sodium chloride can also lead to damage but the intensity is not as evident in comparison with sodium sulfate. The extent of salt attack strongly depends particularly on the environmental conditions and salt content in the material. The morphology of crystals (NaCl, Na₂SO₄ and mixture of both in ratio 1:1) and phenomena related to dissolution were studied with optical microscope. Conclusions from microscopic observation were applied to real porous system - sandstone subjected to salinization and wetting-drying cycles. The massive damage (>50%) showed the specimen containing single sodium sulfate crystals which are during wetting subjected to phase transition accompanied by volume change. The damage caused by sodium chloride and by mixture was much lower - 1% and 3% respectively. Such low mass change could be explained by greater amount of efflorescence and also by lower damage potential of NaCl and the mixture.

This paper presents a complex multidisciplinary approach to characterize the torsional shear on thin-walled cocciopesto lime mortar tubes. The approach employs (i) an in-house developed biaxial electro-mechanical loading frame designed for torsional loading, (ii) an optical measurement setup based on the digital image correlation technique to monitor and record the deformation during loading and (iii) a numerical model using finite element simulation to assess localization of shear failure. Prior to torsional loading, the mortar specimen needs to be firmly secured into the loading frame without exposing it to unwanted tensile or bending loading and possible crushing at fixture points. During the torsional loading, the mortar tube must be able to freely move axially. An optical measurement setup based on the digital image correlation technique allowed to quantify deformation measurements during torsional testing and provided the strain field on the observed surface. The mode of torsional failure was finally assessed from finite element simulations and compared to experimental measurements.

The capacity of various consolidating liquids to strengthen weak mortars is reported in this paper. Commercial products (CaLoSiL IP 15, KSE 100) and liquids prepared in laboratory by dissolving chemicals in water (barium hydroxide, ammonium oxalate, ammonium phosphate) or by dilution more concentrated products (Syton X 30) were used for the experiment. In order to study the influence of the mineralogical composition of the mortar, various sorts of sand were alternatively used in the experiment for the mortar preparation. The efficiency of the treatment was evaluated as mechanical strength change measured on different shape specimens - on tubes for compression strength, on thin plates for tension test and on beams for flexural strength. All the tested consolidation agents showed positive strengthening effect when they were used for consolidation of the poor lime mortar, with the exception of the influence of lime water on the flexural strength. Very different results were achieved on soil-based mortar.

This paper deals with development and validation of a novel device for investigation of the crack behavior in quasi-brittle materials using radiographically observed flexural testing. Instead of standard horizontal arrangement of three-point bending devices, a novel approach consisting in a vertically oriented four-point bending setup is proposed. In the paper, technical description of the proposed device together with its advantages over existing methods and results of validation experiments with natural rocks are presented. The validation experiments were concentrated on the ability of the device to capture the fracture behavior of the samples using X-ray transmission radiography and 4D X-ray micro-tomography. Particular attention was paid to evaluate the ability to perform tomographic scans during post-peak softening, i.e. on intermittent loading of samples after formation of the crack. The acquired results showed very good performance in terms of both the mechanical characteristics of the device (stiffness and loading precision) and the X-ray imaging properties.

Inconel 718 superalloy is one kind of important metallic materials used for manufacturing turbine discs in aero-engine. Since the turbine disc usually bears overloading which will lead to the low cycle fatigue (LCF) damage in real working, and because it is added with high ratio alloying elements, it is meaningful to decide the relationship between the LCF degradation and microstructure evolution. In the present study, LCF behavior of Inconel 718 alloy during long-term aging was investigated. The microstructure evolutions of Inconel 718 alloy during long-term aging at 750 °C for 500, 100, 1500 and 2000 h, respectively and the influences of long-term aging on the LCF behavior were investigated. The results show that the size of γ″ phases increases and the volume fraction decreases with the increase of aging time, compared with the increase of both size and volume fraction of δ phases. Both the fatigue strength and fatigue life of the alloy decrease with the increase of aging time.

The modulus of elasticity, resistivity and capacitive reactance were determined for carbon nanotube reinforced mortars, near percolation. It is shown that the abrupt decrease of the resistivity values observed at the CNT content of 0.1 wt% is associated with the onset of percolation. Mortars reinforced with 0.1 wt% CNTs exhibit an 89% increase in Young’s modulus. Values of resistivity and capacitance are 27% and 90% lower than that of the plain mortar, respectively. After the conductive network is formed, resistivity values show a little dependence on the CNT content, reaching a plateau. Capacitance on the other hand was increased by an order of magnitude, showing an amplified energy storage ability, probably due to the existence of small CNT agglomerates. The observed relationship between capacitance values and modulus of elasticity may provide valuable information on the actual CNT dispersion state in the matrix.

Existing research has demonstrated that FRP confinement is effective for circular columns, whereas it is less effective for square columns. The lower FRP confinement effectiveness in a square column is predominantly attributed to the non-uniform FRP confinement in the column, while the concrete in an FRP-confined circular column is uniformly confined. An appropriate approach to enhancing the confinement effectiveness of FRP strengthening technique for square columns is to circularize a square column before FRP jacketing. This paper aims to study the compressive behavior of circularized square columns (CSCs). A total of 33 column specimens were prepared and tested under axial compression in this paper. The test results have indicated that the section circularization of square columns can significantly improve the effectiveness of FRP confinement, and strengthening square columns using section circularization in combination with partial FRP confinement is a promising and economical alternative to the fully FRP strengthening technique. Comparisons between the theoretical predictions and the test results were conducted, and the accuracy and reliability of existing partially FRP-confined concrete models were also examined.

Fiber-reinforced polymer (FRP) jacketing or wrapping has become an attractive strengthening technique for concrete columns. Within this strengthening technique, FRP composites are wrapped around the concrete column with the fibers in the jacket being oriented in the hoop direction. In practice, the FRP jackets can be either continuous or discontinuous along the column height and thus the resulting column is referred to as fully or partially wrapped FRP-confined concrete columns. Existing research has demonstrated that the partially strengthening technique by discrete FRP strips is a promising and economic alternative to the fully FRP strengthening technique. Although a number of experimental investigations have been conducted on partially wrapped FRP-confined concrete columns, the stress-strain behavior of FRP-confined concrete in partially wrapped concrete columns is not yet understood. This paper presents an experimental program to investigate the axially compressive behavior of circular concrete columns partially wrapped with FRP strips. The test results are presented and compared with the predictions from a typical analysis-oriented stress-strain model to examine its reliability and accuracy. It has been demonstrated that the model provides reasonably accurate predictions of the ultimate axial stress of partially FRP-confined concrete while it usually underestimates the ultimate axial strain.

The effects of varied weight fractions of multi-walled carbon nanotubes (MWCNTs) on the dry sliding wear characteristics of Ti6Al4 V were investigated in this study. Dry sliding wear tests were conducted at three applied load levels of 5, 15 and 25 N on spark plasma sintered unreinforced Ti6Al4V alloy and MWCNTs reinforced Ti6Al4V composites containing 1, 2 and 3 wt% MWCNTs respectively sintered at 1000 °C. The ball-on-flat test configuration with tungsten carbide (WC) as the counterface material was used during the tests. Wear scars and debris were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) techniques. It was observed that the wear resistances and coefficients of friction for the composites were significantly improved over that of the unreinforced Ti6Al4V alloy. Worn surface analysis showed the prevalent wear mechanisms at low and high applied loads were adhesive and abrasive wears respectively. Wear debris analysis by EDX showed the presence of tungsten (W), which suggests a transfer layer of the counterface material. Wear resistance enhancement in the composites was directly related to the extent of MWCNTs dispersion within Ti6Al4V matrix, the interfacial bond strength between the matrix and the reinforcement, as well as the presence of hard TiC interfacial product.

The possibilities of strain measurements in composite structures using optical fiber strain sensors based on Bragg gratings are demonstrated. Specifics of interaction of the sensors with the environment were considered. Indications of optical fiber sensors can be used to predict mechanical behavior of composites structures as well as internal defects development based on numerical models. An approach to numerical modeling for identification of the most critical zones in terms of the appearance and development of delamination defects in polymer composite structures is proposed. Computational results for the case studies are presented.

This paper deals with numerical modelling of rock fracture under dynamic loading. For this end, an anisotropic viscodamage-viscoplasticity model for rock is developed. In the viscodamage part of the model, the Rankine criterion indicates the tensile stress states leading to rate-dependent anisotropic damaging. The anisotropy of damage is based on the compliance damage tensor given by the dyadic product of the gradient of the Rankine criterion with itself. In compression, the inelastic deformation and compressive strength degradation is governed by a Mohr-Coulomb viscoplasticity model. The model performance is first demonstrated at the material point level using a two-element model. Then, the dynamic Brazilian disc test, involving both shear and tensile fracture types along with strain rate hardening, on rock is simulated as a laboratory sample level problem.

Defects kinetics is analyzed as specific type of the criticality in out-of-equilibrium system “solid with defects” – the structural-scaling transition. Defect induced mechanisms of structural relaxation are linked to the generation of different types of the collective modes of defects, that have the nature of self-similar solutions: auto-solitary waves related to multiscale plastic strain localization and blow-up dissipative structures providing the damage localization kinetics. The subjection of solid responses to mentioned self-similar solutions is analyzed both theoretically and experimentally with the goals to link strain and damage localization effects under adiabatic shear failure, splitting of shock wave fronts, the power law universality of fragmentation statistics and failure wave initiation and propagation with specific types of multiscale collective modes of defects. The data of high resolution experiments is analyzed according to developed theoretical approach.

This paper presents a generalization of the widely used approach of Orowan for calculating the roll pressure in flat rolling of homogeneous rigid perfectly strips on viscoplastic sheets. In contrast to the original approach, the approach for viscoplastic sheets requires the analysis of the velocity field since the model is rate dependent. The present paper employs the solution for plane strain compression of a viscoplastic block for finding the through thickness distribution of stress and velocity. Strain rate hardening is taken into account by means of the Herschel-Bulkley model.

The strain rate intensity factor is the coefficient of the leading singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. This factor can be used to describe the generation of fine grain layers in the vicinity of friction surfaces in metal forming processes. However, a difficulty is that the strain rate intensity factor follows from singular solutions and commercial finite element packages are not capable of finding this factor. In the present paper, the upper bound technique is used for this purpose. The kinematically admissible velocity field chosen accounts for the exact asymptotic expansion of the equivalent strain rate. Therefore, an approximate value of the strain rate intensity factor can be found from this field.

3D print of composite materials is one of the rapidly developing areas of additive manufacturing technology. This technology is using (instead of advanced FDM or SLA technologies) materials reinforced by short or micro fibres (mainly carbon or glass fibres). These fibres are oriented mainly in direction of filament extrusion. This is causing transverse- isotropic mechanical properties of final part. Composite materials with short fibres has higher modulus of elasticity, higher strength in bending, better thermal stability and higher impact resistance. These properties can be defined by change of volume rate between matrix and reinforcement. It is noticed nowadays, that these materials are more used in automotive and aerospace industry.Composite materials reinforced by continuous long fibres are on the highest level in area of 3D printed composite materials. These fibres (in direction of extrusion) leads to printing of materials, which tensile strength is at higher level comparing to conventional used aluminium alloys. Orthotropic properties of these materials is the biggest technical problem of this technology. Strength of final material is in direction perpendicular to the extrusion equal only to the strength of matrix (polymer material). This value is much lower comparing to strength of fibres. This disadvantage has to be considered as an input parameter during designing process and product has to be loaded with respect to this property. Orthotropic properties of printed composite material with long continuous fibres has to be taking into account during designing process.Quality of input material and technological parameters has to be carefully checked during 3D printing process and during replacing of parts made from conventional metal materials also. All these parameters (shape of part, combination of thin and thick walled areas, print axis orientation, print layout and defaults layer thickness) are affecting the heat load in printed composite part.Internal stress and deformation can occur during printing process and after removing part from printer. These deformations have an undesirable influence on the dimensional accuracy and mechanical properties of final composite part.Most of 3D printers producers are declaring minimal deformation values, but during experiment described in this article was approved, that specific initial conditions (geometrical properties and process values) can lead to deformations up to order of millimetres. These deformations can occur after print but also after several days (relaxing of material). This paper is dealing with dimensional stability and internal stress of 3D printed parts from composite materials.

Advanced creep resistant tungsten modified 9%Cr martensitic steel (ASTM Grade P92) is a promising structural material for the next generation of fossil and nuclear power plant. The P92 steel has been used to construct new coal-fired ultra-supercritical (USC) power plants with higher efficiency. Creep behaviour and fracture processes in creep are phenomena of major practical relevance, often limiting the lives of power plant components and structures designed to operate for long periods under stress at elevated and/or high temperatures. The creep behaviour of P92 steel has widely been reported. Furthermore, in recent years, extensive experimental studies and thermodynamic modelling of the microstructure and its stability during high-temperature creep of P92 steel have been published. Unfortunately, there are rather few published reports on damage processes in P92 steel during high-temperature creep, and the effect of damage evolution on the creep strength is nor fully understood at present. Therefore, it is not surprising that there are different and often controversial opinions about the role of secondary phases resulting from the additions of high concentrations of tungsten and molybdenum in P92 steel. In addition to M₂₃C₆ carbides and MX carbonitrides, an intermetallic Laves phase Fe₂(W,Mo) is another dominating precipitating phase.

At the beginning of the 20th century, a new wood manufacturing technology, i.e. cross-laminated timber (CLT), was started. In Taiwan, the manufacturing technology of CLT has just started recently. For the sake of safety, the information of stiffness and strength of the shear wall of the CLT are essential for structural designs. In this paper, by following the method B (ISO 16670 Protocol) of ASTM standard E2126-11, shear test of a real-scale CLT shear wall was performed. The measured shear modulus and cyclic test results of the CLT shear wall were reported in this paper. By using the three-dimensional digital image correlation technique, full-field deformation information of the CLT shear wall were obtained.

Modulus of Elasticity (MOE) can be raised by optimizing the mix proportions, increasing the compressive strength and using stiffer aggregates. Unfortunately, such concrete is relatively brittle and has a high propensity of autogenous shrinkage cracking. This study proposes a novel way to improve the modulus of elasticity of concrete without increasing its compressive strength and brittleness, by using carbon nanotubes (CNTs) and carbon nanofibers (CNFs).

To unlock the efficiency of carbon nanofibers (CNFs) in potential applications, it is necessary to take into consideration their distribution in cement-based materials. In this work, it is observed that the relationship between flexural strength and electrochemical impedance properties such as capacitance and resistivity may provide valuable information on the actual CNF dispersion state in the matrix and a method to optimize flexural strength in reinforced mortars.

This paper deals with composite materials usage in design of recuperative member. This member is designed as parallelogram and it is used as energy storage in winding device. This member consist of two linear springs, made from fibre-reinforced composite (carbon T700S with epoxy matrix MTM57). These two springs are mounted on both sides in aluminium brackets.

Additive manufacturing (AM) is today one of the fastest growing industries. Previously, this technology was called Rapid Prototyping. The term ‘rapid prototyping’ (RP) was used in a variety of industries to describe a process for rapidly production of parts before final release or commercialization [1]. Today, this term is not current, because now 3D printing is not used only for fabricating prototypes, but it is increasingly used for small-series production of final parts. This leads to higher requirements on sufficient strength and stiffness of these parts. This problem can be solved using advanced numerical simulations, which also allows to found appropriate solution in combination with structural optimizations. There are many types of structural optimizations (such as geometry, topography, topometry, shape or topology optimization). Topology optimization is one of the best optimizations for this purpose because it can find the best use of material within a given design space [2]. Its use is often overlooked because the final optimized shape of the part is often too complicated for conventional manufacturing technologies, but it is not for AM technologies.The goal of the paper was to find the appropriate methodology for optimizing a part for FDM fabrication using numerical simulations and topology optimization. The first stage of the intake system of a Yamaha YZF-R6 engine for a one-seat racing car was used as a typical part (a case study) for optimization. The simulation was done with respect to temperature. The PA6 copolymer with short carbon fibres was used as the material for the printed part. Experimental tensile testing of this material at temperatures up to 160 °C according to ISO standards was done to find the mechanical parameters [3]. The transverse isotropic mechanical properties of the material with high temperature dependency were found (see Figs. 1 and 2).The optimization was done using the NX Nastran 12 Topology Optimization solver with special manufacturing constrains for AM which allow the creation of a design with respect to minimum thickness of the walls, maximum angles for overhangs and an internal lattice structure.The optimized structure of the part with respect to FDM AM technology and sufficient stiffness and strength of the design was found using the designed methodology. The mass of the currently manufactured aluminium alloy part was reduced by more than 68%.

This paper presents recent advances in the modelling of porous hyperelastic materials the pore space of which is filled with an ideal fluid. The incorporation of hyperelastic behavior of the porous skeleton enable the application of the developments to biological materials such as brain matter and arterial tissues and soft industrial materials that are impregnated with a fluid. The theory accounts for the coupled hyperelastic deformations of the porous skeleton and fluid flow through the pore space. The coupled multiphasic theory is applied to examine certain canonical problems involving one-dimensional compression, radial and spherical expansion of annuli and pure shear of poro-hyperelastic materials. The analytical solutions to these problems are used to benchmark computational approaches.

The main motivations for this study arise from the need for an assessment of the fatigue performance of DMLS produced Maraging Steel MS1, when it is used in the “as fabricated” state. The literature indicates a lack of knowledge from this point of view, moreover the great potentials of the additive process may be more and more incremented, if an easier and cheaper procedure could be used after the building stage. The topic has been tackled experimentally, investigating the impact of heat treatment, machining and micro-shot-peening on the fatigue strength with respect to the “as built” state. The results indicate that heat treatment significantly enhances the fatigue response, probably due to the relaxation of the post-process tensile residual stresses. Machining can also be effective, but it must be followed (not preceded) by micro-shot-peening, to benefit from the compressive residual stress state generated by the latter.

This work derives its motivations from the increasing interest towards Additive Manufacturing and the lack of studies, mainly in the field of fatigue. The effect of build orientation and of allowance for machining on DMLS produced Maraging Steel MS1 has been assessed. The experimental results, properly set up by tools of Design of Experiment, have been statistically processed and compared. The outcomes were that, probably due to effect of the thermal treatment, machining and material properties, the aforementioned factors do not have a significant impact on the fatigue response. This made it possible to work out a global curve, accounting for all the result. Fracture surfaces have been carefully studied as well.

The swift advancement of the computer power and the recent advances in the numerical techniques, and improved strength and failure material models, resulted in accurate simulation of manufacturing processes and events, such as stress optimization during lamination process of polymers and impact into multi-layer opaque and transparent armor configurations. Parametric analysis of materials of known material models can contribute to the development of future materials. The systematic numerical analysis of the effect of material properties, such as modulus of elasticity, yield strength and ultimate tensile strength, on the performance of various systems can provide researchers and manufacturers crucial design information for the technologies of the future. This paper presents the modeling efforts at U.S. Army Research Laboratory (ARL) to develop a correlation between failure mechanisms and the material properties obtained experimentally leading to future materials technologies for personnel protection.

Compare to unidirectional laminates, the preparation of fiber bundle composites is relatively simple. Previous studies have shown that fiber bundle composites and uni-laminates demonstrate similar failure features in the standard Iosipescu shear tests. But a considerable different strength value is observed between the two kinds of specimens. In this paper, three types of fiber bundle composites and uni-laminates were prepared using two kinds of carbon fibers and epoxy resins. The shear strength of fiber bundle composites and uni-laminates were compared to explore the underlying mechanisms resulting in the different shear strength. It is found through the analysis of the interfacial stress field between fiber bundle and matrix using the interface element method that the interfacial stress state in fiber bundle composite specimen is a coupling of tensile stress and shear stress, whereas the interface in unidirectional laminate specimen is in an ideal shear stress state. This difference makes the fiber bundle composites fail at a lower shear stress level. In this paper, a strength model was proposed to bridge the shear strength of fiber bundle composites and uni-laminates using Yamada-Sun strength theory. The experimental verification shows that the shear strengths of the uni-laminate predicted by the proposed model reach a good agreement with the measured values, with the relative deviation of that about 10%.

There are present high temperature experiments of Al and Ti specimens in a high temperature creep up to fracture. The arm of the research is strain localization in the stretched specimens at various initial tensile stresses.

Limited mineral resources amount induce research in natural gas sequestration from non-conventional reservoirs with shale rock being a prominent example. CO₂ based fracturing is promising technique for both shale rock fracturing and greenhouse effect causing gas underground storage, however CO₂ in the presence of water might be corrosive for traditional materials used in natural gas wells limiting their performance in static and dynamic loading conditions. The aim of this work is to develop minisamples based technique for Fatigue Crack Growth (FCG) rate testing on casing pipe material used in conventional gas mining. 3-point bending type samples of three different W dimension has been selected for testing with FCG standard based approach as well as with optical, noncontact displacement measurements made with Digital Image Correlation (DIC) near the propagating crack tip. Results of different testing techniques for P110 steel have been discussed and conclusion drawn out giving general guidelines for proposed method usage in pipeline materials investigation. Additionally scale effect on FCG results has been revealed.

In this paper, a micro-scale stress measurement system was developed to non-destructively measure the laser cutting residual stresses on the edges of ultra-thin glass plates. Three 50 μm thickness ultra-thin glass plates with different laser cutting processing procedures were measured. Experimental results showed that the difference between these three ultra-thin glass plates not only in stress value but also in stress distribution can be clearly identified by the micro-scale stress measurement system.

Noting the fact that the phase and phase derivatives carry the information on the mechanical deformation in optical interferometric measurements techniques, we propose a noise robust fringe analysis technique for the simultaneous estimation of unwrapped phase and arbitrary order phase derivative from a phase fringe pattern. The continuous phase along row or column of the phase fringe pattern is approximated as a weighted linear combination of linearly independent basis functions such as Fourier basis. The weights are accurately estimated based on a state space analysis using the linear Kalman filter. Simulation and experimental results are provided to substantiate the applicability of the proposed method.

Three conic calibration targets (CCTs) were designed and implemented for three-dimensional (3D) digital image correlation (DIC) camera calibration. To understand the associated performance of CCTs and the potential problems while using CCTs to determine the camera parameters, in this paper, the CCTs image data and the corresponding spatial distance were first utilized to determine the camera parameters, and then the 3D CCT object was reconstructed with the same images and the determined camera parameters of different camera-pairs from different viewing directions. Based on the calculated deviations of the overlapping regions of the reconstructed 3D CCTs, it is clear that the proposed CCTs can be used for determining the camera parameters.

An optical measure system is developed to measure transverse deformation of stressed materials. The paper discusses two problems to be solved in the measure system. Experimental results show that the constructed system works well.

In the past two decades, external bonding of carbon fiber reinforced polymer (CFRP) composites is widely used for strengthening reinforced concrete (RC) structures of highway bridges [1]. Researchers have demonstrated that external bonding of CFRP can obviously improve the fatigue performance of RC structures [2]. However, although the super measures have been taken to limit overload from truck, the overload phenomenon is still widespread for highway transportation in China.Therefore, in order to prove the fatigue property and reliability of the RC members strengthened with CFRP in highway bridges under the vehicle overload, experimental study on fatigue performance of RC beams strengthened with CFRP under variable amplitude overloads is carried out in this paper.

Compared with the reinforcement technique with non-prestressed Carbon Fiber Laminate (CFL) for reinforced concrete (RC) structures, prestressed CFL can Increase the cracking load of the strengthened members and make the existed crack closure. In this paper, numerical and experimental methods were applied to investigate fatigue crack propagation behavior of reinforced concrete (RC) beams strengthened with prestressed carbon fiber laminate (CFL).

Stresses in several Prince Rupert’s drops (PRDs) were measured with integrated photoelasticity. Measurements show that the surface layer of thickness about 0.5 mm of the head of a PRD is under high compression stresses reaching at the surface the value of about 500 MPa. That explains the extraordinary strength of the heads of PRD’s. The external part of the tails of PRD’s is also under high compressive stress reaching at the surface the value of 600 MPa. Internal part of the tail is under high tensile stresses. Stress distribution in the tail is used to explain catastrophic disintegration of the tail when it is cut.

The paper performs a series of SHPB experiments using the material of polymethyl methacrylate (PMMA). 8 lengths of cylindrical specimens are designed. The 8 length specimens can be divided into two groups based on two different diameters. Under the identical loading, which means the specimens are all subjected to the identical incident pulse, the failure strengths of the specimens do not show the well acknowledged strain rate sensitivity as the strain rates increase with the decrease of specimen lengths. It is concluded that the strain rate sensitivity of failure strength has to be further clarified as the sensitivity of loading strain rate that one can define it as the strain acceleration.

Mechanical models are developed to determine the mode I and II adhesion toughness of monolayer thin films using circular blister tests under the pressure load. The interface fracture of monolayer thin film blisters is mode I dominant for linear bending with small deflection while it is mode II dominant for membrane stretching with large deflection. By taking the advantage of the large mode mixity difference between these two limiting cases, the mode I and II adhesion toughness are determined in conjunction with a linear failure criterion. Thin films under membrane stretching have larger adhesion toughness than thicker films under bending. Experimental results demonstrate the validity of the method.

An exact solution of symmetric problem on the elastic equilibrium of piece-homogeneous isotropic plane with the interface of media in the form the sides of angle, which contains an interior semi-infinite loaded crack is constructed by the Wiener – Hopf method. The stress behavior near the corner point is investigated.

The main assumptions of the physical and mathematical models of the compatible development of stress-strain state and voids of ductile fracture of welded pipeline elements and pressure vessels with local corrosion-erosion metal losses in weld area have been given to determine the characteristic features of limit state of defective structures. Methods for probabilistic estimation of stressed state of the structures from the point of view of fracture susceptibility have been developed. They are based on the integration of the calculated field of principal stresses within the framework of Weibull statistics. For a correct quantitative assessment of state of critical structures based on complex analysis of the limit state of steel pipelines under internal pressure and different temperatures, functional dependences of Weibull coefficients on metal properties were obtained. Following the typical cases of exploitation damage in the main and technological pipeline elements the specific features of limit state under the different exploitation conditions have been investigated.

The challenge and demands of environmental protection and energy saving have been more and more serious tasks in some processing technologies of glass industry. Significant effort is being carried out for the development of advanced technology for precision casting of spinner discs for glass industry (glass wool) and high temperature applications up to 1050 ℃. In this paper a study creep fracture processes of two different cobalt-based superalloys Co Stelit and Co Ursa Stelit was investigated. Constant load uniaxial stress creep tests in tension were carried out at three different testing temperatures of 900 ℃, 950 and 1000 ℃ and at the applied stress ranging from 40 to 200 MPa. A mutual comparison of the creep characteristics of the investigated alloys under comparable creep loading conditions shows that the cobalt based superalloy Co Stelit exhibits more brittle character of fracture than superalloy Co Ursa Stelit. By contrast, the values of time to fracture (creep life) are longer for the superalloy Co Stelit in comparison to those for superalloy Co Ursa Stelit. The analyses of creep data indicate that creep behaviour of the superalloys under investigation obey both Monkman-Grant and its modified version. The creep fracture modes of these superalloys were determined using empirical formulas based on a continuum damage mechanics approach. The values of damage tolerance factor λ correspond to mixture of transgranular and intergranular type of fracture of both superalloys.

Nonclassical problem of fracture mechanics for two parallel cracks under the action of compressive loads, directed along cracks were investigated. The axisymmetrical problem for penny-shaped crack is considered. There are two approaches that are used to investigate such problems “beam approximation” and three-dimensional linearized theory of stability of deformable bodies for finite and small subcritical strains. Within the limits of the offered in second approach the problem is reduced to the solution of system of integral equations Fredholm with a side condition. Using the Bubnov-Galerkin method and numerically analytic technique, the problem was reduced to system of linear equations. As an example numerical research for a composite material was conducted. Critical loads are obtained for small and large distance between cracks. Results for the composite materials behavior are also present and discussed.

Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material directions were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. Crack growth was modelled using a rate-dependent cohesive zone. The problem was analyzed using Abaqus, and the crack growth experiments were simulated. The experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.

Based on field data and a tailored set of accelerated life tests, the hinge kit system (HKS) of a closing door in a refrigerator was redesigned to improve its lifetime. Using a force and moment balance analysis, the mechanical impact loads of HKS were calculated in closing the refrigerator door. At first ALT the kit housing in the HKS fractured. When breaking up HKS, oil damper was leaked. The failures of 1st ALT were similar to those of the failed samples obtained in the field. The HKS housing and oil damper was modified. At 2nd ALT, the cover housing fractured. The cover housing in HKS was changed from plastics to Aluminum. After two rounds of parametric ALT with corrective action plans, reliability of the new HKS is guaranteed to be over B1 life 10 years with a yearly failure rate of 0.1%.

The present contribution reviews some recent results on the experimental characterisation of the nanoscale fracture toughness of silicon by using pre-cracked specimens and alternatively the theory of critical distances (TCD). Later, the results are discussed to provide the ultimate dimensional limit of the continuum fracture mechanics at the nanoscale in the light of sophisticated discrete atomic simulations at the onset of brittle fracture. The results show that the fracture toughness of Si is independent of the scale, crystal orientation and the singular stress field length. This confirms the atomistic nature of the brittle fracture. Moreover, the continuum fracture mechanics fails below a singular stress field approaching 2 nm.

Interest to mechanical behavior of metal melts is associated with both the development of experimental technique and the possible technological applications. One of the essential properties is the dynamic tensile strength of melts, that is, the level of negative pressure, which leads to cavitations and further fracture of the melt. The tensile state of melt is metastable, like for solid. Molecular dynamic (MD) simulations show that the complete fragmentation of melt occurs when the pore volume fraction reaches 80% or more. The work done by the negative pressure maintained in the melt at the stage of bubbly liquid can exceed the work to reach the cavitations limit due to the longer exposure time. In this paper we investigate with the help of MD the late stages of melt fracture with special attention to the study of the character of the size distribution of cavities and its evolution during tension.

The aim of this study was to recreate cracks network in a rock material during hydraulic fracturing process using the Discrete Element Method implemented in the ESyS-Particle software. We have investigated the behavior of brittle material under tensional stress induced by fracking fluid pumped either with constant velocity or with constant pressure. With DEM approach it was possible to check how the fluid expands inside the rock formation under different conditions. Consequently, we have calculated the injection velocities for different values of pressure as well as a spatial extension of cracks in the material. It gave an insight into hydraulic fracturing process which is possible only using computer simulations.

In recent years, dynamic techniques to partially or fully disintegrate structures utilizing electrical energy have been proposed, which may be more controllable than other conventional dynamic demolition methods, for instance, blasting by explosives. So far, by applying electric discharge impulses in the field, we have performed fracture experiments of relatively small brittle concrete specimens, and together with our finite difference numerical investigations, we have pointed out that the development of fracture network depends very sensitively on the geometrical settings in the specimens (e.g. positions of blast holes (energy sources), empty dummy holes, free surfaces and interfaces to reflect and/or diffract waves and control crack propagation directions). Here, we continue our study and observe that even for dynamic disintegration in more realistic, large concrete slabs, the geometrical settings do play a crucial role and in this case, pre-set slits have strong effect on wave propagation and eventual dynamic fracture pattern. Our three-dimensional numerical code for a PC may well explain the experimental results, suggesting that further research to find the optimal geometrical settings for more predictable and controlled dynamic structural disintegration should be conducted from the wave dynamics point of view.

Electron back-scatter diffraction method was applied to analyze the degradation process of Ni-base superalloy Alloy 617 under various loading conditions at elevated temperatures from the view point of the change of the order of atom arrangement in grains and grain boundaries. The local damage evolution around grain boundaries was evaluated by applying the intermittent creep and creep-fatigue tests. The creep-fatigue test was operated at 800 °C under the stress of 150 MPa with strain rate of 0.4%/s and hold time of 10 min in inert gas (99.9999% Ar). Each test was stopped at a certain strain and the micro texture was evaluated step by step at the same area in each test sample continuously. The crystallinity of grains and grain boundaries was evaluated by applying image quality (IQ) and confidence index (CI) values obtained from EBSD analyses. It was found that degradation of the crystallinity was accelerated at certain grain boundaries drastically and the first crack always initiated at a grain boundary when the IQ value decreased to a critical value. It was also confirmed that this degradation decreased the strength of the grain boundary. Finally, it was concluded that the strength of a grain boundary was dominated by its crystallinity and there was a critical IQ value at which a crack initiated at the grain boundary.

The results of studying the problems on the fracture of composites containing interacting cracks under the action of forces directed along the cracks are reported. Given are the descriptions of two non-classical failure mechanisms – the fracture of compressed bodies under the action of forces directed in parallel to the planes containing cracks and the fracture of composites with residual stress acting along cracks. We use a combined approach to investigate the abovementioned fracture mechanisms within the framework of linearized solid mechanics. Spatial problems on composites that contain interacting circular cracks are considered. Problems on an infinite body containing two parallel co-axial cracks and on a space with the periodical set of co-axial parallel cracks as well as those on a half-space with subsurface crack are solved. Several patterns of loading on the crack faces (normal loading, radial shear and torsion) are considered. The effects of residual stresses on stress intensity factors are analyzed for some types of composite materials. Critical fracture parameters for composites with interacting cracks compressed along the cracks are calculated using the approach mentioned. The effect of geometrical parameters of the problems as well as physical and mechanical properties of materials on these critical parameters is analyzed.

On the basis of a modified $$ \delta_{c} $$-model of crack, the limiting state of an orthotropic plate made of a material satisfying the general strength condition and weakened by a system of collinear cracks is studed. The relations for the determination of major parameters of the model of cracks (the size of process zones, stresses in these zones, and the crack-tip opening displacements) are deduced. The mechanism of fracture of the plate containing a periodic system of collinear cracks is investigated. The influence of the degree of anisotropy and geometric parameters of the problem on the formation of the process zones and limiting state of the plate is revealed. The region of safe loading of an orthotropic viscoelastic plate with cracks is determined. The influence of the rheological parameters of the material on the region of safe loading is analyzed.

Generalized stress intensity factors H _k (GSIFs) are the necessary parameters to describe stress state near bi-material junction tip by means of asymptotic series. GSIFs can be determined as a least square method solution of overdetermined system of linear equations. The equations consist of analytical eigenfunctions, which are determined as a solution of eigenvalue problem and results of finite elements analysis (FEA), in form of displacement or stress components. The study presents the application of the overdeterministic method on bi-material junction problem. The effect of number of input values from FEA and the radius of their extraction on resulting H _k is studied. The study also shows how number of calculated singular and non-singular terms affects values of individual factors. The results are compared with results of the Psi-integral method. Once the GSIFs are determined, stress solution on particular diameter by asymptotic series is compared with pure FEA results.

A fatigue testing method for micro-metals using resonant vibration was developed. For the control of the fatigue cycle, we designed a gold micro-cantilever specimen with a weight at the tip, which reduced the resonant frequency. The tension-compression fatigue cycle was applied to the specimen using a piezoelectric actuator. The characteristic slip bands along the primary slip system, which possesses the highest Schmid factor, were generated on the specimen surface. Although the slip bands had similar morphologies to those of persistent slip bands (PSBs) in bulk, they were much narrower (width: approximately 50 nm) and needed a higher formation stress.

By simultaneously operating high-speed digital video cameras, we have been experimentally investigating the mechanical characteristics of ice spheres that impinge upon a fixed elastic plate consisting of ice/polycarbonate. We have found that, when ruptured under dynamic impact, ice spheres show two specific fracture patterns: “top” and “orange segments.” Our three-dimensional finite difference calculations simulating impact on linear elastic spheres indicate that “top” (“orange segments”) fracture pattern is generated due to a shorter (longer) contact time during the impact process, respectively. Here, using pressure sensors, we try to clarify more quantitatively the generation mechanism of two dynamic fracture patterns. The new experimental observations suggest that the rise time (the time needed to reach a certain pressure owing to impact) is basically shorter when the generated fracture is the “orange segments”-type. This shorter rise time renders a longer effective contact time and hence waves of longer lengths, consistent with our earlier speculations.

Structural failures are often related to mechanical destabilization of fracture in brittle solids that are subjected to some loading conditions. Either dynamically or quasi-statically, fracture areas (cracks) may be initiated and developed in or between solid structural elements, which may serve as sources of catastrophic failures. In reality, multiple cracks, not only a single one, may expand simultaneously and interact with each other mechanically. The collective behavior of such multiple cracks, however, does not seem to have been intensively studied so far. This contribution summarizes our recent experimental investigation into the nonlinear deformation of a solid material that is initially linear elastic but containing sets of cracks. Together with the earlier mathematical prediction [1], it is shown that the prescribed constant rate of strain, externally applied to a solid with multiple cracks, plays a crucial role in determining the overall stress-strain relation and eventually the tensile strength of the solid material.

Presented is a rigorous mathematical formulation of boundary value problems defined on discrete systems described by mathematical graphs. The formulation is applicable to mechanical and physical problems and includes an effective algebraic framework and efficient computational implementation. Mechanical problems involving damage initiation and evolution are soled to illustrate the proposed method. It is concluded that the graph-theoretical approach to discrete systems offers substantial benefits in terms of conceptual clarity and computational efficiency.

The subject of this research is multi-segmented, telescoping, beam-like structures, which represent an important class of engineering systems with, in general, nonuniform geometric and physical parameters. The distributed parameter Euler-Bernoulli sectioning methodology applied to such structures produces a transcendental eigenvalue equation that requires a numerical root-funding algorithm. This study provides evidence that for continuous system upper modes, root finding algorithm is subject to numerical instability due to the finite precision associated with software and hardware used for the computations. The results obtained after extensive numerical computation and analysis of three-segment cantilever telescoping beams with two lap joints, yield new insights into the prediction of the numerical instability and the role computational issues may play in the solution of distributed parameter eigenproblems.

Recently, new techniques have been presented that discretize continuous elasticity variables as cochains over a primal mesh, representing the solid, and an appropriately defined dual one. Discrete strain and stress can be then thought of as a vector-valued 1-form (or vector-valued 1-cochain on the primal mesh) and covector-valued 2-form (or vector-valued 2-cochain on the dual mesh) respectively. The governing equations can be formulated by requiring energy balance and invariance under time-dependent rigid translations and rotations of the ambient space. To obtain those, we project the discrete stress into normal and tangential components and formulate the boundary value problem with a system of two matrix equations. This allow for treating both classical and coupled-stress (micro-polar) elasticity. The link between discrete strains and stresses is provided by a material discrete Hodge star operator, which we define to include geometric and physical factors, such as lengths, areas, and moduli of elasticity and rigidity. The performance of the proposed formulation is demonstrated by a simple example.

Some problems of strength and stability of thin constructions with defects and inclusions, which are of vital importance for nano- and microtechnology, are investigated. The attention is paid to the estimation of the number of defects influencing the capacity for work of nanosized plated and shells. The influence of surface effect is taken into account.

Increase in strain rate requires an increase in density of lattice defects (dislocations) necessary for plastic relaxation of the increasing shear stress. Irradiation of metals by intensive femtosecond laser pulses creates compression waves with durations of tens of picoseconds and ultra-high strain rates up to an inverse nanosecond. At such strain rates, multiplication and motion of the initially existing dislocations become not enough for restriction of the shear stress, which can grow up to the limit of homogeneous nucleation of dislocation loops. We investigate regularities of the homogeneous nucleation of dislocations in metals with FCC, BCC and HCP lattices using the molecular dynamic simulations. Then we generalize these regularities in the form of continuum model of plasticity with nucleation and apply the model for simulation of shot compression pulses. It allows us to investigate the transition between the common mode of multiplication and the nucleation-controlled mode of plasticity.

The incremental behaviour of a prestressed, elastic, anisotropic and incompressible material is analyzed in the dynamic regime, under the plain strain condition. Dynamic perturbations of stress/deformation incident wave fields, caused by a shear band of finite length, formed inside the material at a certain stage of continued deformation, are investigated. At the base of the proposed dynamic perturbation approach is the time-harmonic infinite-body Green’s function for incremental displacements obtained by Bigoni and Capuani [5] for small isochoric and plane deformation superimposed upon a nonlinear elastic and homogeneous strain. The integral representation relating the incremental stress at any point of the medium to the incremental displacement jump across the shear band faces, is obtained. Finally, a numerical procedure based on a collocation method is used to solve the boundary integral equation for incident wave scattering by a shear band.

The mechanical response of a lead-core bearing device to a real, near-fault, strong ground motion is simulated by performing a finite element analysis.

A dynamic analysis method for face gear grinding machine is proposed to guide the structure optimization design of weak part. Firstly, dynamic analysis, harmonic response analysis and modal analysis of machine tool are implemented using ABAQUS. The analysis result indicates that the machine tool bed and spindle are key structures affecting the dynamic performance of the machine tool. Secondly, take the machine tool bed and spindle as optimization goal to optimum design their structures, respectively. Meanwhile, establish their optimal design model, thus the machine tool bed and spindle structure are optimized by harmonic response analysis and modal analysis. Finally, the analysis results demonstrate that the proposed method can improve dynamic performance of the machine tool effectively. On the premise of the machine tool bed and spindle mass do not increase, all the six nature frequencies of the whole machine tool are increased to different degrees after the optimum design.

As there is an increasing demand for high performance turbo-machinery hydrodynamic bearings are expected to run at high speed and high load operating conditions with low power loss and oil flow. Bearings play a critical role to achieve machine’s overall reliability level. This paper reviews various analytical and experimental studies that have been done on hydrodynamic bearing performance published in various journals. The analytical study brings challenges in formulating the boundary conditions consideration of thermal effects on governing equations effect of turbulence and consideration of re-circulating oil with incoming oil in inlet oil groove etc. Experimental studies pose the challenges on the measurement of performance parameters such as temperature distribution oil film distribution etc. From the survey, many researchers found that thermal and turbulent effects had the considerable impact on predicting accurate static and dynamic performance of the hydrodynamic journal bearing.

The autowave theory of plastic flow of materials is suggested. It is shown that this is based on the elastic-plastic invariant, which connects the elastic and plastic parameters of deforming solids. The consequences from the invariant describe correctly the principal features of plastic flow.

The present work aims to compare the residual strain fields of the austenitic stainless steel 316L samples under specific loading conditions, obtained by different techniques. Experimentally, Digital Image Correlation (DIC) technique is used to track the (residual) strain maps during the specimen loading. Microstructure-based Finite Element (FE) models based on two different approaches for the material behavior (Crystal Plasticity (CP) and SNF) provide the numerical results. The quality of the outcomes reinforces the use of a combination of these techniques to study the residual strain locations in the microstructure, as well as its evolution during the deformation process. Whereas the results based on CP and SNF showed good agreement, some minor differences between calculated and measured (DIC) strains could be observed.

Stress concentration, size and surface state were believed to be the main factors for the fatigue endurance strength and fatigue life of a component contrasting to a smooth standard test specimen with the same nominal stress. Especially, there are complicated interactions among these factors.

Placing posterior atlas screws is technically demanding, and a misplaced screw can result in serious medical consequences. However, the current surgical approach and choice of internal fixation technique are usually decided according to the doctor’s personal experience and preferences. The purpose of this paper was to set up an integrated solution for screw placement of posterior atlas fixation, using 3D interactive visualization anatomic measurement and biomechanical simulation analysis. The atlas posterior arch screw demonstrated the lowest risk factor for damaging nearby tissues. The three mainstream posterior internal fixations can provide similar stability for the odontoid fractures. Atlas pedicle screw generated the lowest stresses on screws showing it stabilizing capability. The three fixations have the ability to offer enough stability for atlantoaxial instability caused by odontoid fractures, and each with its own set of merits and demerits. The results of this study can serve as process for customized surgical planning.

Residual Stresses are an aspect of material state that is complex in many different respects. As any stress quantity, it has multi-component tensor nature, so that at each point up to 6 components need to be determined. Moreover, in contrast with ‘live’ stresses, residual stresses (RS) cannot always be determined by tracking their evolution from an initial state. Furthermore, RS are scale-dependent, so that if the resolution (gauge volume) of the measurement is changed, so does the perceived stress state. In the context of RS ‘measurement’, conventional classification into Type I, II and III (macro-, micro- and nano-scale stresses) is often used, but the intricate relationship between these quantities remains insufficiently well understood. Finally, the interaction of RS with material processing and service behaviour introduces further associated complexities, and deserves additional discussion.

Plastic deformation of metallic glasses, if exerted at low homologous temperatures with respect to the glass transition temperature, is mostly localized in plate-like mesoscopic defects, so-called shear bands. Although the occurrence of shear bands is well known and often determines the mechanical performance of the material, their actual physical properties remain fairly unknown. Additionally, it is widely accepted that localized regions, so-called shear transformation zones, undergo plastic yielding through a shear transformation at low strains. Yet, how those localized regions are distributed, in what way they are structurally distinct from the surrounding matrix and how they couple to evolve into shear bands with macroscopic lengths at higher strains is also unclear. This contribution addresses those coupled questions and issues by combining complementing experimental methods and – for selected situations – results from atomistic simulations [1–11]. Here, experimental data on the rate of atomic diffusion within shear bands have been obtained using the radiotracer method on post-deformed specimens. Those measurements that had been performed at temperatures below T_g on samples after they underwent plastic deformation, showed a drastic increase of the atomic mobility inside the shear bands. In fact, as indicated in Fig. 1, the diffusion coefficient inside the shear bands was found to be more than six orders of magnitude larger than the diffusion coefficient of the undeformed matrix of the same material.Fig. 1.Diffusion coefficients of radioactive Ag and Au isotopes in Pd₄₀Ni₄₀P₂₀ bulk metallic glass. The diffusion coefficients in the shear band (blue) were measured after deformation by cold rolling. Remarkably, the activation enthalpy for diffusion inside the shear bands amounts to only one third of the activation enthalpy for bulk diffusion. This large difference indicates large modifications of the atomic structure inside the shear bands.

Finite element analysis (FEA) of tensile loading of nano-scale double edge notched (DEN) metallic glass (MG) specimens are conducted using a non-local plasticity model. The effects of notch acuity on the plastic deformation response of the samples are studied. Transition is observed from localized plastic deformation by single shear band (SSB) to necking of the ligament and further to double shear bands (DSBs) with increase in notch acuity. These results corroborate with molecular dynamics (MD) simulations and are rationalized from spread of plastic zone in the ligament.

The excellent combination of high strength and low stiffness make bulk-metallic glasses (BMGs) candidate materials for many structural applications. Their fracture toughness, however, can vary markedly, and their ductility, particularly in tension/compression, is rather limited, although in bending they are quite ductile. Here, we report on a systematic study on Zr and Pd-based glasses to investigate the influence of sample size on the fracture toughness of BMGs. Results show that with decreasing sample size the fracture behavior changes from brittle failure with low fracture toughness, via a semi-brittle failure regime, to fully ductile fracture and non-catastrophic failure with sub-critical crack growth, i.e., R-curve behavior.

The aim of this study is to show that new types of bulk metallic glass composites (BMGCs) can be produced via severe plastic deformation (SPD). The initial materials are mixtures of a Zr-metallic glass (MG) and crystalline Cu powders that were mixed and then consolidated, cold welded together and refined by high pressure torsion (HPT). Four different compositions (Zr-MG Xwt% Cu, X = 20, 40, 60, 80) were produced as well as single phase Zr-MG samples as reference. To investigate the influence of the degree of deformation and the ratio of the two phases on the evolution of the microstructure and mechanical properties, scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness and microcompression measurements were used.

Structural inhomogeneity and defects caused in the forming process in metallic glasses lead to some weak areas (such as free volumes and liquid-like zones) embedding into the glassy phase, which are associated with the plastic flow. The energy introduced by an ion irradiation can change the number and distribution of free volumes. The irradiation at low dosage can change the structure by increasing the density of free volume, thus resulting in a decrease in the strength. The irradiation at high dosage makes nanocrystallization occurring in the metallic glass. The analysis of relaxation spectrum suggests that the relaxation strength increases, and then decreases with increasing the irradiation dosage. The results of this study highlight the fact that a large amount of free volumes can be achieved through a low-dose ion irradiation, which can modify the mechanical behavior of metallic glasses.

Bulk metallic glass matrix composites (BMGMCs) with metallic dendrite reinforcements combine the excellent strength, hardness, and elastic strain limit of amorphous metallic glass with a ductile crystalline phase to achieve extraordinary toughness with minimal degradation in strength. In order to explore the mechanical interactions between the amorphous and crystalline phases a full-field micromechanical model, which couples a free volume based constitutive model for the matrix with crystal plasticity, has been implemented in an elastic-viscoplastic Fast-Fourier Transform (FFT) solver. The findings indicate that in BMGMCs, local inhomogeneities in the glass phase are less influential on the mechanical performance than the contrast in individual phase properties. Due to the strong contrast in mechanical properties, heterogenous stress fields develop, contributing to regionally confined free volume generation, localized flow and softening in the glass. In these softened regions, plastic flow rapidly localizes into shear bands.

Owing to their glassy nature, metallic glasses demonstrate a toughness that is extremely sensitive to the frozen-in configurational state. This sensitivity gives rise to the so-called “annealing embrittlement”, which is often severe and in many respects limits the technological advancement of these materials. Here, equilibrium configurations (i.e. “inherent states”) of a metallic glass are established around the glass transition, and the configurational properties along with the plane-strain fracture toughness are evaluated. An association between the intrinsic toughness and the inherent state properties is attempted in an effort to identify the fundamental origin of embrittlement of metallic glasses. The established correlations reveal a one-to-one correspondence between a decreasing toughness and an increasing shear modulus, which is robust and continuous over a broad range of inherent states. This annealing embrittlement sensitivity is shown to vary substantially between metallic glass compositions, and appears to correlate well with the fragility of the metallic glass.

Bulk metallic glasses (BMGs) possess high strength, but their fracture toughness and fatigue crack growth resistance can vary widely. Fracture toughness and fatigue crack growth results for Zr-based BMGs show that fracture toughness is highly sensitive to the glassy micro- and/or nanostructure, while the fatigue crack growth resistance is relatively insensitive. Soft and heterogeneous glassy structures promote crack tip blunting and high fracture toughness, and can be promoted by thermo-mechanical treatments. During fatigue cycling, in-situ free volume generation occurs ahead of the crack tip that defines the local structure independent of the initial structural state. Accordingly, fatigue crack propagation rates depend little on the initial structure of the BMG. Finally, synchrotron XRD analysis of crack-tip strain fields revealed that the crack-tip deformation extends farther, and is more homogeneous, than visible shear bands suggest and the mechanism of fatigue crack propagation is identical to crystalline metals despite the different deformation mechanism.

The aim of the current work is to study the microstructure stability under thermal and mechanical loads of a nano-structured Cu/Co alloy and nc-Nickel with different content of solute elements and nano-particles. For this annealing at different temperatures as well as fatigue loading are performed and the microstructure evolution is characterized. The effectiveness of mechanisms that impedes grain growth (solute drag, Zener pinning) are evaluated and studied for both, thermal and mechanical loads.

Methods of severe plastic deformation (SPD) can be principally applied to all kinds of metallic materials and are widely used to generate nanocrystalline materials that frequently exhibit improved mechanical and functional properties. The resistance against crack growth is, however, only rarely studied despite its importance for the damage tolerant design of components. In this contribution general tendencies found for the fatigue crack behavior of a large variety of SPD-processed metals and alloys, including pure metals (iron and nickel) but also alloys (NiTi, steels) is given. In general grain refinement leads to a deteriorated fatigue crack growth behavior, which can be mainly attributed to a reduction of crack closure contributions. Another significant factor seems to originate from the frequently observed transition from transgranular to intergranular fatigue fracture possessing a lower crack growth resistance than transgranular crack growth. Based on these general observations strategies to counteract these tendencies are discussed where especially the grain-aspect ratio of the microstructures may play an important role.

The temperature rise in shear bands is of significant importance for the mechanical behaviour of metallic glasses since it changes their atomic structure and viscosity. However, experimental measurement of any temperature rise of a shear band is difficult, due to their temporal and spatial localization within the bulk. Molecular dynamics simulations were carried out on a CuZr metallic glass under tensile loading. It is shown that the observed temperature rise in a shear band, ranging from ~25 K up to the melting point of the alloy, correlates linearly with the maximum sliding velocity of the shear band, which is a function of both sample size and loading rate. In response to the high energy flux into the shear band, shear band bifurcation occurs and hinders further temperature rise well above the melting point. This negative feedback mechanism imposes an upper limit of temperature rise in a shear band before the theoretical limit of shear velocity is reached.

Metallic glasses are known for their outstanding mechanical strength but limited plasticity. Significant progress has been made in recent years in how to optimize processing conditions for bulk glass formation, net-shape forming and the microscopic mechanism of failure. However, the details of the correlation between atomic structure, defects and thermo-mechanical treatments utilized for structure modification and their impact on shear band nucleation and propagation for achieving macroscopic ductility are still not well understood.This talk attempts to shed light on structural (re)ordering, recovery and rejuvenation mechanisms, as well as nanocrystallization phenomena in different metallic glasses when they are subjected to different casting conditions, relaxation or thermoplastic net shaping. The findings will be discussed with respect to short- and medium-range order modulation, defect generation and annihilation, and precipitation of secondary phases. The structural changes will be correlated with changes in plastic deformability and failure mechanisms, and the effectiveness of composition tuning and thermo-mechanical processing for plasticity improvement will be analyzed in order to derive design aspects and processing guidelines for property optimization of metallic glasses.

We have studied the influence of different loading rate and different radius of spherical indenter on the nano-indentation creep process of {(Ce0.2La0.8)0.78Ni0.22}75Al25 at room temperature and describing the creep behavior by using elastic-viscoelastic principle. With the increase of loading rate, the strain rate sensitivity increases, due to the activation of multiple shear zones at higher loading rate, causing the materials becoming soften. Comparing the parameters between the spherical indenter of 2 μm and 5 μm, the values under 2 μm are much bigger, because large size of STZ under 2 μm enhance shear capacity of BMG, promoting the occurrence of multiple shear zone, increasing the ability of plastic deformation, leading a larger displacement. These results highlight the fact the important parameters getting from the creep function are all have different degrees of loading rate sensitivity and compared the data of different radius of spherical indenter, concluding “the smaller, the stronger”.

Bulk metallic glasses are an exciting class of materials. Their mechanical properties are fundamentally different from their crystalline counterparts, due to the disordered structure. An experimental understanding of the fundamental deformation mechanisms of metallic glasses at the nanoscale is still lacking. Therefore, in situ deformation is carried out inside a transmission electron microscope. Scanning nanobeam electron diffraction is used to map the local elastic strain during deformation. The strain maps are determined by fitting an ellipse to the first order diffraction ring at every probe position. A direct electron detector enables acquiring the diffraction patterns at a sufficient speed to perform strain mapping during continuous in situ deformation.

Plastic deformation proceeds through a sequence of stochastic local slip followed by load redistribution. With continued deformation this builds up complex stress fields and develops a heterogeneous pat- tern of local strength, leading to the emergence of microvoids and cracks. The goal of this research is to develop a coarse grained model for crystal plasticity that captures the physics emergent form stochastic heterogeneous deformation. The method based on the discrete element method (DEM), an approach developed for modeling of granular materials and recently adapted for amorphous brittle solids. DEM models the material as a collection of interacting elements. The framework naturally captures the elastic coupling due to geometric frustration in a system under heterogeneous deformation and the emergent phenomena that develop from it. This paper presents the accomplishment of intermediate steps towards modeling crystal plasticity: modeling anisotropic elasticity, and modeling isotropic plasticity.

Here, we report on experimental studies of metallic glass and nanocrystalline materials and novel synthesis and processing routes for controlling the structural state – and as a consequence, the mechanical properties. A particular focus will be on strategies for rejuvenation of disorder with the goal of suppressing shear localization and endowing damage tolerance. We also describe a microscopic structural quantity designed by machine learning to be maximally predictive of plastic rearrangements and further demonstrate a causal link between this measure and both the size of rearrangements and the macroscopic yield strain. We find remarkable commonality in all of these quantities in disordered materials with vastly different inter-particle interactions and spanning a large range of elastic modulus and particle size.

The vibration-absorbing properties of the plate under the action of a spherical harmonic wave in the soil are studied. In the soil model, an elastic isotropic medium is used. The main goal is to determine the total vector field of accelerations. The mathematical formulation of the problem includes the assignment of the incident wave, the equations of motion of the soil and the plates, the boundary conditions for the slab and the soil, the conditions at infinity, and the conditions of contact of the earth with the obstacle, where we neglect the connection of the plate to the ground. The motion of the plate is described by the system of equations of Paimushin V.N. The kinematic parameters of the plate and the parameters of the disturbed stress-strain state of the soil are represented in the form of double trigonometric series satisfying the boundary conditions. After that, the constants of integration, displacement and vibration acceleration are determined.

A technique for the analysis of nonhomogeneous transversally-isotropic materials is suggested for the case of 3D elasticity formulation. By making use of the direct integration method, the formulated problems are reduced to a set of governing equations for the stress-tensor components. In order to construct the solutions to the latter equations in an explicit form, an advanced solution technique is developed on the basis of the resolvent-kernel method.

The key features of the thermal- and thermo-stressed analyses for the thermosensitive structures are considered for the case of complex heat-exchange with the surroundings. A nonlinear boundary-value problem of heat conduction is formulated and the analytical-numerical solution methods are presented. For the determination of the thermoelastic state in the bodies of such kind, the thermoelasticity equations with variable coefficients are implemented. The solutions to the later ones are constructed by making use of a technique that is similar to the perturbation method.

The paper considers plain nonstationary contact problems for perfectly rigid die translating into an elastic half-space. As a general case, the boundary of the contact area is assumed to be moving one. The method of functionally invariant solutions is used as a tool of analytic solution and study of distribution of contact stresses. By making use this method, the formulations of the problems are reduced to Riemann-Hilbert problem. It is shown that the distribution of stresses near the boundaries of the region differs for four ranges of contact speed: superseismic, first transseismic, second transseismic and subseismic. It is also shown that in the case when the given stresses or displacements are arbitrary continuous functions, the problem reduces to the considered way with help of approximating the given functions by homogeneous polynomials. The authors found and studied the analytic solution of the problems of indentation with conical and parabolic dies.

This paper studies a linear two-dimensional non-stationary problem of a viscoelastic half-plane with normal displacements applied on its boundary.The solution is presented in the form of generalized convolution of the corresponding solutions of two-dimensional problem for elastic half-plane and one-dimensional problem for viscoelastic half-plane. Both solutions are written as convolutions of boundary conditions with surface Green functions as kernels. To build Green functions Laplace time transform is used. Two-dimensional elastic half-plane problem is written in potentials. Inversion of the transforms is carried out analytically. For plane elasticity theory problem analytic representations of the transforms are used, for one-dimensional viscoelastic problem the transform is expanded in series in powers of relaxation kernel which is taken in the form of two-parameter exponential function. As a result formulas for normal and tangential stresses at the boundaries of viscoelastic half-plane are obtained. This allows analyzing the distribution of stresses in time and coordinate and comparing it with the solution of the corresponding problem for elastic half-plane.

The problems of propagation of non-stationary waves in linear viscoelastic bodies on condition that the Poisson’s ratio of the material does not change through the time are considered. The issues of finding of the solutions of such problems by the method of Laplace transform in time are discussed. The general form of the solution in transforms is presented. The case when a hereditary kernel is an exponential two-parametrical one is considered. We have demonstrated that in such case the singular points of the Laplace transforms are connected by a simple relation with singular points of the Laplace transforms for the corresponding elastic body. There have been conditions established under which the poles of transform have the first order and the original is simpler. As an example, the analytical solution of the problem of one-dimensional non-stationary longitudinal wave propagation in a viscoelastic cylinder is presented. This solution is valid within the whole range of time without the assumption of smallness of viscosity.

A vertical impact of fluid-filled spherical shells (indenter) with a rigid barrier (foundation) is investigated. The contact between the shells and the filling and between the shell and the foundation is adhesive-free. The basic resolving integral equation resulting from the boundary condition caused by the impact between the shells system and the foundation is obtained. The kernel of this equation is the transient function for a system of shells with a filler. The transient function for the indenter is constructed analytically with help of Laplace integral transform and Fourier series. The system of governing equations is derived, and the numerical-analytical algorithm of solution of the formulated problem are described.

To solve the problems about arbitrary oriented defects in anisotropic quarter plane, a method based on the use of the space of generalized functions with slow growth properties was developed. Two-dimensional integral Fourier transform was used to construct the system of fundamental solutions for anisotropic quarter plane with the concentrated jumps of stresses and displacements in this space. The latter allows the problems about the defects to be reduced to systems of singular integral equations (SIE) with fixed singularities. As an example the problem about the crack exiting to the boundary of the quarter plane has considered, for which the system of SIE with fixed singularities is obtained. To determine the singularities’ indexes of the stresses and displacements at the vertices of the quarter plane and of the crack the transcendental equations are obtained. The asymptotic behavior of the solutions is investigated. The efficient numerical-analytical method for solving systems of SIE with fixed singularities is proposed.

In the space of generalized functions of slow growth $$ {\Im }^{{\prime }} ({\mathbb{R}}^{3} ) $$ a discontinuous solution of the stationary thermoelasticity problem for a piecewise homogeneous transversally isotropic space is constructed in the case of arbitrary loading. Using the constructed discontinuous solution and the properties of the functions from $$ {\Im }^{{\prime }} ({\mathbb{R}}^{3} ) $$, two-dimensional singular integral relations are obtained which allow the problem of interphase defects in an inhomogeneous transversely isotropic space allow to reduce to systems of two-dimensional singular integral equations (SIE) with kernels that are expressed in terms of elementary functions. An exact solution of the thermoelasticity problem for interphase circular inclusion is constructed, which is in complete coupling with different transversely isotropic half-spaces. Expressions for the jumps of the normal and tangential stresses are obtained and the dependences of the translational displacements of the inclusion on the temperature, the resultant load, the main moment, and the thermomechanical characteristics of transversely isotropic materials are obtained.

The coupled unsteady electromagnetic processes in a multicomponent elastic solid taking into account the diffusion are investigated. A general model of thermoelectromagnetoelastic diffusion is presented for an arbitrary anisotropic continuum in a curvilinear coordinate system. The transition from the general formulation to the one-dimensional problem of electromagnetoelastic diffusion in the Cartesian coordinate system is done. To solve the problem, the Laplace transform and the Fourier expansion are used.

Exact analytical approach for plane stain investigation of piezoelectric/piezomagnetic bimaterial with magnetically permeable and electrically conducting crack located at the interface between its components is suggested. It is assumed that a normal and shear stresses field and also the electric and magnetic fields paralleled to the crack are given at infinity. First, an open crack is considered, and then it is assumed that the crack faces may have a frictionless contact at a certain section of unknown length, which is adjacent to one of the crack tip. In the last case the combined Dirichlet-Riemann boundary value problem and Hilbert problem have been formulated and the exact analytical solution has been presented. For both cases a numerical illustrations of the obtained solutions were done for different values of mechanical and electric fields at infinity. The dependence of magnetic, electric and mechanical characteristics on the mechanical load and electric field were investigated.

An analytical-numerical method for the investigation of steady-state wave fields in an unbounded elastic medium scattered by a non-canonical form of elastic fiber in the presence of a thin piezoceramic interphase of variable thickness and low stiffness is proposed. The components of the electroelastic system are in perfect mechanical contact; the electric induction is zero on the surface of the interphase. The interphase material belongs to the 6 mm crystallographic class. The elastic system is in the conditions of antiplane motion. The research algorithm is based on the modified null field method. The influence of mechanical and geometric parameters of the composite on the amplitude-frequency characteristics of SH-waves scattered by a fiber of non-canonical form into a far-field zone is analyzed.

The focus of this work is to derive the averaged 2D dynamic theory for elastic sandwich plates of symmetric structure on thickness which can describe the stress-strain state asymptotically correct on long waves and qualitative correct on sufficiently short waves. The governing two-dimensional dynamic equations for sandwich plates are derived with the help of variational asymptotic method worked out by Berdichevsky [1] and which is used to rigorously reduce three-dimensional problem into two-dimensional problem.

Unsteady oscillations of a thick-walled sphere under the action of a mechanic and electric fields on its surfaces are considered. The expansion in serieses on Legendre polynomials and the Laplace time transform are used. The inverse Laplace transform is performed using a specially developed algorithm.

Structural integrity and lifetime assessment of nuclear power plant components and RPV requires a responsible data on residual stresses. A significant complexity of experimental measurement of residual stresses in existing RPV prevents taking them into account in evaluation of safe operation. Significant progress in computer simulation of welding stresses and their interaction with temperature and operational loads using modern mathematical methods creates preconditions for more precise evaluation of non-relaxed residual stresses in RPV taking into account the real technological parameters of multi-pass welding, cladding of corrosion protective layer and PWHT. Using exist and calculated precise data the influence of residual stresses in the nozzle zone of RPV WWER-1000 on brittle strength during PTS event was evaluated.

In the present paper we consider the problem of describing the dynamics of material with complex rheology, when it is necessary to take into account that it consists of several subsystems with different relaxation times. Such approach, in which the deformable solid is considered as a multicomponent medium, greatly expands the possibilities of continuum mechanics allowing to describe the processes, occurring at different scale levels. Here this problem is demonstrated by using the example of the interaction between the crystalline lattice and the electron gas. The experiments on different conductors demonstrate that their dynamic response on a laser pulse of nanosecond duration is different from the form predicted by classical theory of thermoelasticity. In this case it should be supplemented by equations describing kinematics of the electron gas, which may exert a serious influence on behavior of the lattice, resulting in significant increase of the stretching phase in comparison with the classical solution.