Mechanics of Composite, Hybrid and Multifunctional Materials, Fracture, Fatigue, Failure and Damage Evolution, Volume 3

Advanced composite materials exhibit many desirable characteristics which make them viable candidates for utilization in harsh marine environments. An experimental investigation has been conducted to quantify the effects of coupled water saturation and low temperatures on the mechanical and dynamic behavior of E-glass and carbon epoxy laminates. The relative performance of the materials as a function of water saturation and decreasing temperature was characterized through detailed experiments, specifically in-plane (tensile/compressive) and shear material properties, static and dynamic Mode-I fracture, and impact/flexure after impact strength. The temperature range considered in the study corresponds to a range from room temperature (20 °C) down to Arctic seawater and extreme ocean depth conditions (−2 °C). The materials utilized in the study, carbon/epoxy and E-glass/epoxy, are chosen due to their primary interest to the marine and undersea vehicle communities. The results of the mechanical and dynamic material experiments show that all properties are affected by both water saturation and decreasing temperature, although the trends are specific to the property of consideration.

Fracture toughness of an engineering material is an essential parameter for the damage and the safety assessment of a structure exposed to different loading conditions in applications like defense, automotive, and aircraft structure. In this article, an effort is made to evaluate the fracture toughness of AA7475-T7351 alloy under different loading rates. Single edge three-point bend experiments are conducted at four different loading rates 1 mm/min, 10 mm/min, 100 mm/min, and 1000 mm/min. Quasi-static experiments are conducted using two different electromechanical universal testing machines (Zwick-Roll/Z-50 and MTS). Quasi-static initiation and propagation fracture toughness are evaluated from the load vs. crack mouth opening displacement (CMOD) diagram. It is observed that the fracture toughness of the material increases with the increase of loading rates. The fracture propagation toughness of the material also shows a positive sensitivity towards the loading rates.

In this study, an effort has been made to investigate the mechanical behavior including the fracture toughness of AA5083 aluminum alloy under different loading rates. EDX-spectroscopy is performed to evaluate the chemical composition of the aluminum alloy AA5083. The quasi-static tensile and compressive experiments are performed on a universal testing machine. The quasi-static three-point bend experiments are performed using the MTS-810 machine to obtain the static fracture toughness of AA5083 aluminum alloy. The quasi-static tensile tests and compression tests are performed at different strain rates (10⁻⁴ to 10⁻¹/s) and flow stresses have been obtained for the corresponding strain rates. It is found that the aluminum alloy shows strain rate sensitivity in both tension and compression; however, this sensitivity was relatively more dominant in tension than in compression.

In this century, as fossil energy resources are becoming increasingly scarce and their negative effects on the environment are being felt more and more every day including global warming and air pollution, the trend towards renewable energy sources is growing worldwide. Among the various renewable energy systems, wind energy stands out for its cost-efficiency and sustainability. In favor of higher wind speeds, offshore wind turbines generate significant potential for electricity production for coastal countries. However, high wind speeds, as well as open sea rains, have certain disadvantages on turbine blades, such as wind erosion damage. In addition, the rotor blades are moving rapidly due to the high wind speeds and they are hardly noticed by the birds, resulting in bird collisions with the wind turbine blades. This generates an impact load on the blades, which damages the blades of the wind turbine. Therefore, the impact resistance of the wind turbine blades must be improved for reliable service life. This study aims to develop composite materials to be used in the manufacture of wind turbine blades. In this respect, effective reinforcements should be used to improve the impact resistance of the developed composites. Accordingly, epoxy-based carbon-glass fiber reinforced composites are manufactured by using fine silicon carbide (SiC) particles as secondary reinforcement. Experimental studies, tensile tests, and impact tests were carried out to characterize the mechanical properties of the manufactured composites. With this study, it is intended to examine the effects of reinforcements on mechanical properties, and to determine an optimal composition to achieve these properties.

In the day we fight against Covid-19, the use of disposable masks and isolation clothing is multiplied by 12 compared to the time before the Covid-19 pandemic. Considering that these disposable masks are made of polypropylene (PP), an average of 480 kilotons of PP waste is produced each year, exclusively from masks. After the use of these masks, it is important to collect and re-evaluate them in a controlled manner so as not to pose a risk of contamination and not to threaten the environment. Because of its advantageous properties, PP is used in the production of many parts in the automotive industry. With this study, it is aimed to develop composite materials to be used in car bumper manufacturing by using recycled PP obtained from melt blown PP fabrics (surgical mask fabric). Due to accidents or road conditions, impact damage can occur on the bumpers. Therefore, the impact resistance of the bumpers must be improved. In addition, in case of microscale damage resulting from the impacts received, microcracks may develop and cause material failure below the maximum tensile stress. In summary, effective reinforcements should be used to improve impact strength in composites for use in car bumpers. Accordingly, novel recycled PP (rPP) based composites are manufactured by using elastomer-styrene-ethylene-butylene-styrene (SEBS) and graphene nanoplatelets (GnPs) as compatible reinforcements with rPP. As experimental characterization, three-point bending tests and Charpy impact tests were carried out. Incorporation of GnPs increased the flexural strength and blending with SEBS improved the impact resistance of the developed composites. Certain clusters of the graphene nanoplatelets were observed by means of microscopy.

In this study, the microstructural formation and static/dynamic compression behaviour of recycled AA7075 based hybrid composites reinforced with ZrO₂and Al₂O₃ fibres were investigated. The effects of the hybrid metal matrix composites on the mechanical behaviour (quasi-static compression, dynamic compression, three-point bending and microhardness) have been investigated in detail by using ZrO₂ as a reinforcement element in two different proportions. It is aimed to be an alternative to traditional alloys used in the aeronautic industry. These composites were produced using by combined sinter + forging processes. The static and dynamic properties have been evaluated in detail, taking into account the relevant Scanning Electron Microscopy (SEM) microstructures (including the distribution of reinforcement elements).

In this study, a novel recycled Al 431 + 1050 based composites reinforced with “TiC” were designed for aeronautical applications with high resistant structure against to choc and static loading under service conditions. Static/dynamic compression behaviours of these composites were evaluated. Basically, laboratory-scale test samples were produced using combined “sinter + forging” production methods. Al 431 + 1050, a mixture of recycled and modified aluminium alloys, was used as the main matrix material. Different proportions of TiC (10, 15 and 20 wt %) were used as a major reinforcement element. As minor reinforcements, Mo and Cu metal powders and a small amount of Graphene Nano Platelets, (GNPs), and Alumina, (γ-Al₂O₃) fibre were used to compare their influence on the mechanical properties of these hybrid composite structures.

In the present work, the hybrid aluminium based composites coming from recycled AA7075 chips are produced by using the different levels of reinforcements. As a major one is TiC ceramic carbide (d ≤ 1–3 micron) at three levels (2.5%, 5%, 10%), whereas the minor addition of MoS₂, Nb2Al and γ-Al₂O₃ fibre were fixed as 2, 3 and 3 wt %, respectively. These compositions are targets for the application of the connection link in a mechanism to transfer motion in aeronautical industry. For this reason, the machinability of these composites should be significant engineering case for the tailored behaviour of the composites produced through combined method of powder metallurgy route: sintering + Forging. Certain characteristics of the composites were carried out according to the optimization conditions of the reinforcements. Static and dynamic-crash tests will be performed. The microstructure analyses (matrix/interface) were carried out by Scanning Electron Microscope (SEM).

A three-dimensional non-linear finite element model was used to simulate the static compression tests behaviour of these composites. A subroutine, VUMAT, will be written to use with ABAQUS/Explicit to analyze the effect of sintered-forging on the micro- and macrostructure of the manufactured materials. Different ratios of reinforcing particulates using in the experimental specimens were used in Representative Volume Element (RVE) (and other distribution techniques, etc.) for the microstructure modelling. Then, numerical models for the macrostructure were created using these micro-structures under the multiscale modelling process conditions.

The copper-aluminium (Cu-Al-Zn-Ni) based structures show shape memory behaviours that are low cost engineering applications, such as actuators, valves, etc., regarding to Ni-Ti-Al structures. These alloys have a useful transformation temperature that can be modified to lie between −100 and 100 °C (sometimes ±50 °C). For low cost production, a combined method through powder metallurgy processes (sinter-Forging) without using the grain size control additives.

In the frame of the common research project, production of the scrap thin sheet copper based composites reinforced with scrap commercially pure aluminium (AA1050) and zinc produced through the combined method, sinter-forging process will be discussed for a tough structure.

In this research, devulcanized recycled rubber modified phenolic epoxy based composites reinforced with different ceramic carbon, and/or glass fibres and also graphene nano plates (GnPs) based composites were designed for aircraft internal structure. After determination of the reinforcements and matrix, a hot bonding process was applied to complete successfully the manufacturing of these composites. After that, the relevant toughening mechanisms given by the reinforcements were analyzed in detail to evaluate the damage tolerance of aircraft internal structures. For this purpose, mechanical and physical properties, K_IC—Fracture toughness stress intensity factor and G_Ic—Critical energy release rate in mode I) have been determined by fracture toughness tests (static 3P bending test with single edge notch specimens, drop weight test, etc.).

In the frame of the common research project, manufacturing of scrap thin sheet “Ni-Ti-Al” based composites reinforced with Nb₂Al/TiB₂ have been carried out through hot-forged bonding process of the composites for a high strength sandwich structure (>1500 MPa). Interface and bonding characteristics have also been examined of hot-forged composites, heat treated at 550 °C depending on the operational parameters under laboratory conditions. Formability behaviour and delamination phenomenon have been analysed by 3P bending tests. An intermetallic phase layer has been carried out between the titanium and aluminium sheets containing hard particles reinforcements during hot forging process. Finally, a high strength bonding has been carried out by mechanical joining and mutual chemical bonding diffusion during this process as a function of process temperature and time.

Numerical Approach: At this stage of the project, the primary objective would be to establish a continuum-based material model in order to capture the macroscopic behaviour of the targeted composite materials and numerically reproduce the results from the basic characterization tests (bending). The model was implemented for Finite Element Analysis Software ABAQUS/Explicit as a user subroutine VUMAT for explicit nonlinear finite element calculations. The second step would be modelling of the microstructure of the proposed hybrid Ni-Ti-Al based composites and simulate the behaviour of several RVEs and see the effect of the sintered-forging and different ratios of reinforcing particulates.

In this project, design of niobium-aluminium (Nb₂Al) intermetallics based composites is proposed by using the fresh scrap recycled niobium and aluminium alloy AA7075. These compositions will be the target for aeronautical engineering applications for high temperature service conditions. Manufacturing of these composites is an important engineering case for tailored behaviour of the composites produced through combined method of powder metallurgy route; sintering followed by forging. Different materials and operational (process) parameters will be used for optimization of the compositions. All of the analyses will be devoted to the static (compression, 3-point bending) test conditions. Microstructure analyses (matrix/interface) will be carried out by Scanning Electron Microscope (SEM). At this stage of the project, the primary objective would be to establish a continuum-based material model in order to capture the macroscopic behaviour of the targeted composite materials and numerically reproduce the results from the basic characterization tests (3P bending). The model will be implemented for Finite Element Analysis Software ABAQUS/Explicit as a user subroutine VUMAT for explicit nonlinear finite element calculations. The second step would be modelling of the microstructure of the proposed hybrid Nb₂Al based composites and simulate the behaviour of several RVEs and see the effect of the sintered-forging and different ratios of reinforcing particulates.

Due to its high impact energy absorption properties, devulcanized recycled rubber based composites can be considered as a low cost candidate material for military applications which require lightweight protection against shock waves. This work aims at modeling of low cost devulcanized recycled rubber based composite behavior at high strain rates. In that framework, we established a continuum-based material model in order to capture the macroscopic behavior of the recycled rubber based composite material and numerically reproduce the results from the basic characterization tests. The model is implemented for Finite Element Analysis Software ABAQUS/Standard as a user subroutine UMAT for implicit nonlinear finite element calculations in order to simulate the behavior of several RVEs representing the microstructure of the composite and it is behavior at high strain rates.

Conventional design of micro-aerial vehicles (MAVs) uses fixed airframe design optimized for the entire flight path. This compromise leads to sub-optimal flight characteristics during certain flight regimes. Birds’ wings show great versatility during various stages of flight using feathers and wrist joints. A new design is proposed using piezoelectric patches known as macro-fiber composite (MFC) embedded directly on the surface of the wing and tail to serve as control actuators. In addition, sweeping mechanism was developed to mimic the folding action of birds for a stable dive maneuver. The use of MFCs and sweeping mechanism for controlling MAVs presents a unique challenge for optimizing the effectiveness of these actuators for all flight maneuvers. Numerical models were developed using structural and aerodynamic tools to optimize the location of the MFCs for maximum deflection and overall aerodynamic performance. Digital image correlation (DIC) was used to validate the full field deformation of the control surfaces under simulated aerodynamic loading.

The growing demand for mineral leads to a significant increase in the number of tailings produced, which exceed the number of ores with economic value obtained. The process to obtain one ton of copper ore generates 90% of the total amount of waste, making urgent the measures to reuse it is tailings. Concrete with steel fiber has been applied in civil construction to improve the mechanical characteristics of the concrete; the steel fiber increases impact resistance, fatigue resistance, cracking control, and concrete post-cracking behavior. Considering that, this work aims to present a new alternative for the reuse of copper ore tailings in the construction industry, through the production of concrete reinforced with steel fibers. The feasibility of using the tailings was investigated by three mixture: a reference mixture (RR) and a mixture with 20% of tailings plus 2% of steel fiber (R1). Both mixtures, the water-cement ratio was 0.5, and plasticizer additive of water reduction was 2%. From the results obtained, it was possible to observe that both R1 presented satisfactory results regarding the mechanical evaluations performed, when compared with RR. Thus, it is possible to say that, considering this aspect, the manufacture of concrete with partial replacement of sand by copper tailings with the addition of steel fiber is feasible.

Fatigue testing methods for metals have traditionally used static test methods that have been modified for cyclic loading. One technique that has not been extensively applied to characterizing fatigue behavior of metals is indentation testing. New manufacturing processes for metals, such as selective laser sintering, are introducing new challenges in characterizing properties where the nature of the process can lead to greater spatial variability, making a technique for characterizing the localized variation in fatigue properties critical. Recently, we explored the use of cyclic instrumented indentation testing for locally characterizing the fatigue behavior of metals. The results indicate that cyclic instrumented indentation testing can be used to obtain fatigue behavior locally in metals, and potentially other materials, such as composites.

Military grade composites are used in many different applications for their low weight to protect the equipment from harm or destruction. In this research, low-cost devulcanized recycled rubber based composites were designed with short glass fibers + glass bubbles reinforcements. After determination (in wt% percentages) of the reinforcements with matrix, a special process was applied to complete successfully the manufacturing of these composites (silanization of the recycled rubber and devulcanization before blending it with epoxy resin and reinforcement). All of the details of these processes were given in former papers (Irez et al., Materials 12:2729, 2019; Irez et al., Polymers 12:448, 2020; Irez et al., Mechanics of composite and multi-functional materials, Springer, pp 59–70, 2017; Irez and Bayraktar, Mechanics of composite and multi-functional materials, Springer, pp 73–80, 2019). After that, the relevant toughening mechanisms for the most suitable reinforcements were analyzed in detail for front and rear parts in the military applications (such as military vehicles, boats, etc.). For this purpose, certain mechanical and physical properties (ISO 13586: 2000), (K_IC—Fracture toughness stress intensity factor and G_Ic—Critical energy release rate in mode I) have been determined by fracture toughness tests (static 3P bending test with single edge notch specimens). Microstructural and fracture surfaces analyses have been carried out by means of scanning electron microscopy (SEM).

Cyclic loading is one of the main causes of degradation of reinforced concrete structures. The behavior of a reinforced concrete structure in fatigue can be represented by mechanical models, based on different theories (damage, fracture, plasticity …), whose development requires knowledge of the characteristic parameters of the material and uncertainties associated. In this paper, we propose a polynomial chaos expansion (PCE) methodology to propagate parameter uncertainties in a damage model. The PCE will also be used to perform a sensitivity analysis of the model. Sensitivity analysis allows quantifying the effects of input variables or their combinations on the output variables of a model. The methodology is illustrated with a reinforced concrete beam subjected to cyclic loading. The results indicate that the deterministic model and PCE are close to the experimental results. The sensitivity analysis was also useful to determine which are the most influencing parameters for a reliability analysis.