Biaxial Tests Research Articles

Graphene oxide increases PMMA's resistance to fatigue and strength degradation.

to characterize the effects of graphene oxide (GO) on polymethyl methacrylate's (PMMA) reliability and lifetime. The hypothesis tested was that GO would increase both Weibull parameters and decreased strength degradation over time. PMMA disks containing GO (0.01, 0.05, 0.1, or 0.5wt%) were subjected to a biaxial flexural test to determine the Weibull parameters (m: modulus of Weibull; σ0: characteristic strength; n=30 at 1MPa/s) and slow crack growth (SCG) parameters (n: subcritical crack growth susceptibility coefficient, σf0: scaling parameter; n=10 at 10-2, 10-1, 101, 100 and 102MPa/s). Strength-probability-time (SPT) diagrams were plotted by merging SCG and Weibull parameters. There was no significant difference in the m value of all materials. However, 0.5 GO presented the lowest σ0, whereas all other groups were similar. The lowest n value obtained for all GO-modified PMMA groups (27.4 for 0.05 GO) was higher than the Control (15.6). The strength degradation predicted after 15 years for Control was 12%, followed by 0.01 GO (7%), 0.05 GO (9%), 0.1 GO (5%), and 0.5 GO (1%). The hypothesis was partially accepted as GO increased PMMA's fatigue resistance and lifetime but did not significantly improve its Weibull parameters. GO added to PMMA did not significantly affect the initial strength and reliability but significantly increased PMMA's predicted lifetime. All the GO-containing groups presented higher resistance to fracture at all times analyzed compared with the Control, with the best overall results observed for 0.1 GO.

Effects of Age, Sex, and Extracellular Matrix Integrity on Aortic Dilatation and Rupture in a Mouse Model of Marfan Syndrome.

Transmural failure of the aorta is responsible for substantial morbidity and mortality; it occurs when mechanical stress exceeds strength. The aortic root and ascending aorta are susceptible to dissection and rupture in Marfan syndrome, a connective tissue disorder characterized by a progressive reduction in elastic fiber integrity. Whereas competent elastic fibers endow the aorta with compliance and resilience, cross-linked collagen fibers confer stiffness and strength. We hypothesized that postnatal reductions in matrix cross-linking increase aortopathy when turnover rates are high. We combined ex vivo biaxial mechanical testing with multimodality histological examinations to quantify expected age- and sex-dependent structural vulnerability of the ascending aorta in Fbn1C1041G/+ Marfan versus wild-type mice without and with 4-week exposures to β-aminopropionitrile, an inhibitor of lysyl oxidase-mediated cross-linking of newly synthesized elastic and collagen fibers. We found a strong β-aminopropionitrile-associated sexual dimorphism in aortic dilatation in Marfan mice and aortic rupture in wild-type mice, with dilatation correlating with compromised elastic fiber integrity and rupture correlating with compromised collagen fibril organization. A lower incidence of rupture of β-aminopropionitrile-exposed Marfan aortas associated with increased lysyl oxidase, suggesting a compensatory remodeling of collagen that slows disease progression in the otherwise compromised Fbn1C1041G/+ aorta. Collagen fiber structure and function in the Marfan aorta are augmented, in part, by increased lysyl oxidase in female and especially male mice, which improves structural integrity, particularly via fibrils in the adventitia. Preserving or promoting collagen cross-linking may represent a therapeutic target for an otherwise vulnerable aorta.

Very High Cycle Fatigue and Ultrasonic Testing in Multiaxial Loading

Abstract Fatigue damage has special relevance on the lifespan of mechanical components and structures, as it takes responsibility for the majority of registered structural failures. Most fatigue testing today still uses uniaxial loads, nonetheless it is generally recognized that multiaxial stresses occur in many full-scale structures. Nowadays, the growing need for greater lifespans forced the study of material behavior under what is nowadays very high cycle fatigue (VHCF) regime, fatigue research beyond 10E07 up to 10E10 cycles. However, most classic fatigue machines are often very costly, both in terms of time and energy, for such an elevated number of cycles. The high costs of equipment and time to conduct such experiments have seen a massive improvement with the introduction of high frequency ultrasonic machines. Presently, it is already possible to characterize materials VHCF response under axial and multiaxial loading conditions in a fraction of the time. Ultrasonic testing machines were first introduced for simpler uniaxial loading and more recently adapted for multiaxial loading conditions. The present work reviews the current background of ultrasonic fatigue testing machines working at 20-kHz frequency, with emphasis on multiaxial fatigue and VHCF. A review of a series of fatigue tests are presented, respectively, axial, shear, axial/shear, and in-plane bi-axial fatigue tests with different combining dimension specimens allowing different shear/axial stress ratios. Special attention will be put into the performance of multiaxial classical cylindrical specimens under tension/torsion and flat cruciform specimens under in-plane bi-axial testing using low-cost piezoelectric transducers. By comparing all so far developed and successfully reached multiaxial specimens and respective methodologies, two base approaches were possible to be established. When designing new specimens or ultrasonic machines, or both, one of the two methods must be followed. To have a well-comprehended methodology and successful design approach will undoubtedly guide future multiaxial ultrasonic method ideas.

Identification of polymer behavior from nonequibiaxial elongation test with temperature and strain rate conditions close to blow molding process

AbstractAn anisotropic visco‐hyperelastic (VHE) model for polyethylene terephthalate (PET) is used to simulate the stretch blow molding process. The biaxiality needs to be taken into account for an accurate identification of the model parameters related to the induced anisotropy. Thanks to the use of a biaxial elongation apparatus developed at MSME, nonequibiaxial tension tests on PET have been managed on optimized specimen in order to provide data complementary to the equibiaxial (EB) tension test. This last enables the correct identification of the temperature and strain rate influence, because both viscous and elastic parts of the model need to test the material in nonequibiaxial (NEB) conditions. The procedure already used for EB tension test is extended to constant width and an intermediate case, NEB cases. The VHE model developed to simulate the PET behavior in the stretch blow molding conditions is identified from these three different biaxial tests: differences and dispersions are discussed. The origin of this dispersion is found out and solved by a modification of the model. This leads to a reduction of the number of parameters in the proposed VHE model.

A Visco-Hyperelastic Constitutive Model to Characterize the Stress-Softening Behavior of Ethylene Propylene Diene Monomer Rubber.

Uniaxial and biaxial cyclic tensile tests and stress relaxation tests were performed on the ethylene propylene diene monomer (EPDM) material to investigate its stress-softening effect. The experimental results reveal that the EPDM material presents a significant Mullins effect during the cyclic stretching processes. Furthermore, it is found that the deformation of the EPDM material does not return to zero simultaneously with the stress, due to the viscoelasticity of the EPDM material. Therefore, this study combines pseudo-elasticity theory and viscoelastic theory to propose a visco-hyperelastic constitutive model. The proposed model is used to fit and analyze the uniaxial and biaxial cyclic test results of EPDM and a comparison is conducted with the corresponding hyper-elastic constitutive model. The results show that the proposed model is in good agreement with the experimental data and superior to the hyper-elastic constitutive model, especially when it comes to the stress-softening unloading process. This work is conducive to accurately characterizing the stress-softening behavior of rubber-like materials at large deformation and can provide some theoretical guidance for their widespread application in industry.

An efficient material point method framework based on the affine matrix

The material point method (MPM) has proven to be an effective numerical approach for simulating extreme events involving large deformations. Although numerous MPM variants have been proposed to enhance the capability of MPM, its application is currently limited by issues of computational efficiency and stability. This study presents an innovative affine matrix-based MPM scheme (AM-MPM) that can substantially promote the computational efficiency of MPM while maintaining exceptional stability. The proposed scheme is featured by its use of the affine matrix as a first-order approximation of the velocity gradient in the subsequent step and the direct computation of associated strain/stress for particles. This approach reduces the information interpolation between particles and grid nodes from two times to a single time, significantly leveraging computational efficiency. The proposed MPM scheme is firstly validated by the quasi-static compaction under self-weight and then applied to various classical problems involving large deformations, including biaxial compression test, column collapse, the impact of two rings, and the twisting of a 3D elastic column. The performance of the proposed scheme in terms of accuracy and efficiency is also discussed in detail.

Modelling the creep behaviour and induced failure of clay rock from microscale viscosity to large-scale time-dependant gallery convergences using a multiscale numerical approach

The large-scale creep behaviour of Callovo-Oxfordian (COx) clay rock is modelled from small-scale viscous mechanisms of the rock using a multiscale numerical approach in the context of radioactive waste repositories. At the mesoscale, the saturated non-homogeneous rock is represented in digital 2D Representative Elementary Areas (REAs) as a cracked composite material consisting of rigid elastic mineral inclusions (quartz, calcite, and pyrite) embedded in a clay matrix. The modelling of these materials is considered within double-scale finite element framework, in which the homogenised responses of the REA to the enforced global kinematics serve as a numerical constitutive relation at the macroscale. To reproduce the rock creeping, two viscous mechanisms have been introduced to consider the creep of the clay matrix: either the viscoplasticity of the clay aggregates or the viscoelasticity of their contacts, or both. Firstly, laboratory biaxial creep tests of clay rock samples are simulated. A three-stage creep stage is reproduced and the creep failure process is discussed. Then, large-scale underground engineering structures are modelled to reproduce its time-dependent behaviour. It is found that the developed multiscale model is able to provide some valuable insights into the large-scale creep behaviour of clay rocks through the morphological and material small-scale characterization of REA.

Biaxial tensile tests to study mechanical behaviour of thin soft materials

The mechanical properties of soft materials such as biological tissues, membranes, fabric, and polymers are anisotropic. For example, young’s Modulus of above materials could be different in different directions. Study of mechanical behaviour of soft materials, thus, involves multi-axial tensile tests. This paper deals with uniaxial and biaxial tensile tests on several different sheets of paper. The experiments were carried out on an indigenously developed benchtop biaxial tensile testing instrument. It has four independent actuators that apply stress in orthogonal directions. Each actuator is actuated using a stepper motor and the stretching force is measured using a load cell. The strain in the central part of the specimen is monitored using Digital Image Correlation (DIC) technique that uses digital images to track the deformation and the strain of a material under load. The instrument is designed for handling thin samples of soft materials and uses an indigenously developed gripping system. It has provision for specimen to have a sample environment that allows temperature variation or submersing of the specimen in suitable liquids (e.g. water, biological fluids). The instrument has a foot print of 400 mm x 400 mm and is portable. Technical details of the above biaxial tensile testing instrument and the results of uniaxial and biaxial tensile tests, both, on dry and wet sheets of paper are reported.

Laser induced high temperature thermal-mechanical-oxygen coupling experimental system and method

In this paper, a thermal–mechanical–oxidation coupling experimental system based on laser heating is developed, containing two modes of Gaussian and flat-top lasers, which has a series of advantages such as high temperature range, rapid heating rate, and convenient observation. The system adopts active illumination and an optical filter to solve the problem where it is difficult for traditional digital-image correlation technology to image clearly under laser heating. A biaxial mechanical test machine is used to simulate the complex load by applying biaxial tension or compression loads on the material. Combined with the radiation temperature measurement and controllable flow field device, the thermal-mechanical-oxygen coupling experiment of high temperature resistant materials under aerobic environment can be carried out. The maximum uniform heat flux output density is 27.2 kW/cm2, and the maximum Gaussian heat flux output density is 105 kW/cm2. The thermal-mechanical-oxygen coupling experimental system and method are of great significance to the development of new high temperature resistant materials and thermal barrier coatings.

Non-associated and Non-quadratic Characteristics in Plastic Anisotropy of Automotive Lightweight Sheet Metals

AbstractLightweight sheet metals are highly desirable for automotive applications due to their exceptional strength-to-density ratio. An accurate description of the pronounced plastic anisotropy exhibited by these materials in finite element analysis requires advanced plasticity models. In recent years, significant efforts have been devoted to developing plasticity models and numerical analysis methods based on the non-associated flow rule (non-AFR). In this work, a newly proposed coupled quadratic and non-quadratic model under non-AFR is utilized to comprehensively investigate the non-associated and non-quadratic characteristics during the yielding of three lightweight sheet metals, i.e., dual-phase steel DP980, TRIP-assisted steel QP980, and aluminum alloy AA5754-O. These materials are subjected to various proportional loading paths, including uniaxial tensile tests with a 15° increment, uniaxial compressive tests with a 45° increment, in-plane torsion tests, and biaxial tensile tests using laser-deposited arm-strengthened cruciform specimens. Results show that the non-AFR approach provides an effective means for accurately modeling the yield behavior, including yield stresses and the direction of plastic strain rates, simultaneously, utilizing two separate functions and a simple calibration procedure. The introduction of the non-quadratic plastic potential reduces the average errors in angle when predicting plastic strain directions by the quadratic plastic potential function. Specifically, for DP980, the average error is reduced from 3.1° to 0.9°, for QP980 it is reduced from 6.1° to 3.9°, and for AA5754-O it is reduced from 7.0° to 0.2°. This highlights the importance of considering the non-quadratic characteristic in plasticity modeling, especially for aluminum alloys such as AA5754-O.

Quantification of inhomogeneity and anisotropy of bituminous mixtures using biaxial experimental data

Most of the existing mechanical characterization test methods and the analytical models for bituminous mixtures are developed based on the assumption of homogenous and isotropic material properties. However, the extent to which such assumptions hold good for bituminous mixtures is not very clear. A biaxial testing scheme in indirect tension mode can come in handy to collect the experimental data at different test temperature regimes. In this study, a bituminous mixture with a nominal maximum aggregate size (NMAS) of 13.2 mm is used to fabricate cylindrical test specimens with 150 mm diameter and 63.5 mm thickness for conducting the repeated load indirect tension (IDT) test. The input load level is selected as 5 to 13 % of the indirect tensile (ITS) failure load in the form of a haversine pulse of 0.1 s loading and 0.9 s rest period. Such loading is applied on zero-degree and ninety-degree orientations of the specimen. The resulting deformations in different directions are measured using linear variable differential transducers (LVDT) attached to both diametral faces of the specimen. The response of the bituminous mixture specimen is captured at three different temperatures of 20, 25, and 30 °C using two different gauge length (half and quarter gauge of the total diameter). A new framework is introduced in this study to evaluate the extent of inhomogeneity and anisotropy of bituminous mixtures. The deformation response of the test specimen captured in the same orientation at different diametral faces is compared to evaluate the extent of inhomogeneity. The extent of anisotropy is evaluated by comparing the deformation response of the test specimen captured at different orientations within the same diametral face. A 15 % variation in the average peak deformation is chosen as the demarcation for determining the extent of inhomogeneity and anisotropy. From this investigation, it is observed that half gauge length experimental data exhibits homogenous and isotropic behavior for all three test temperatures. The quarter gauge length data exhibit similar behavior at 30 °C, whereas it is observed as homogenous and anisotropic at the other two test temperatures.

Effects of hydrate distribution heterogeneity on the mechanical properties of hydrate-bearing sediments with consideration of the coalescence phenomenon: Insights from DEM simulations

The heterogeneous distribution of hydrates in natural or synthetic hydrate-bearing sediments (HBSs) has definitively proven its influences on hydrate dissociation and related mechanical responses, which can alter hydrate production strategies. However, due to the limitations of experimental conditions, applicable hydrate heterogeneity characterization and corresponding evaluation of the mechanical properties of HBSs remain lacking. In this study, discrete element modelling of numerical HBSs with different hydrate heterogeneous distributions considering the coalescence phenomenon is performed. The hydrate heterogeneity degree is quantified through image recognition, and the constructed HBSs are subjected to biaxial compression tests. The results show that for two HBSs with the same hydrate saturation above 10 % but highly different hydrate heterogeneity degrees exceeding 0.1, the peak strength, secant modulus and maximum dilation angle of the strongly heterogenous HBSs are lower than those of the weakly heterogenous HBSs. In addition, the weakly heterogeneous HBSs exhibit a more uniform contact force chain structure, more hydrates participate in loading support, and more particle rearrangements, which are the meso-mechanisms for the above macro-mechanical behaviors. Combined with the consideration of the hydrate morphology and cementing ratio, the mechanical properties of HBSs fluctuate due to the randomness of hydrate coalescence but generally show a decreasing trend with increasing hydrate heterogeneity degree. These findings provide an important supplement for understanding the macro- and meso-mechanical properties of HBSs with different hydrate heterogeneity degrees, which indicates that we should precisely describe hydrate coalescence in laboratory experiments and numerical simulations and consider its representativeness in field applications.

Development of the Forming Limit Diagram for AA6016-T4 at Room Temperature Using Uniaxial Tension of Notched Samples and a Biaxial Test

Development of the Forming Limit Diagram for AA6016-T4 at Room Temperature Using Uniaxial Tension of Notched Samples and a Biaxial Test

Methodology for strength distribution estimation of ceramics from ball-on-three-balls and four-point bending experiments, Weibull statistics and fractographic investigations: Application to magnesium aluminum spinel

The present paper aims to propose a reliable analysis of ball-on-three-balls and four-point bending experiments applied to advanced ceramics combining statistical analyses, numerical modelling and fractography. MgAl2O4 transparent spinel ceramic was selected to facilitate the assessment of samples quality. Following the material processing procedure detailed in the literature, numerous spinel samples of two different geometries (20 and 60 mm in diameter) were produced. Knoop Hardness and Young's modulus values of 11.8 GPa and 290 GPa were measured, respectively. A three-modal grain size distribution was observed through the sample's thickness. Biaxial bending tests have been performed in conjunction with numerical simulations using Abaqus/Standard®. Thus, parallelism defects were taken into account and their effects on the maximal stress and effective volume were quantified. They were found to be very close to the only published data. In addition, four-point bending experiments were carried out and validated using an ultra-high-speed camera. The scattering of the bending strength was modelled using a two-parameter Weibull distribution and the maximum likelihood approach. 90% confidence intervals of the parameters and confidence bounds of the probability of failure were computed using the likelihood ratio test. This approach is more suitable than Monte Carlo simulations with regard to computational costs. According to the Weibull theory and biaxial bending strength distribution, the material strength, rescaled for different effective volumes was slightly overestimated, in comparison with four-point bending results. Fractographic analyses on uniaxial bending samples revealed that fractures originate from large grains. The corresponding study on biaxial bending samples revealed that carbon inclusions located near to the surface seem to be responsible for failure. Finally, this study brings additional arguments for a more intensive use of the ball-on-three-balls set-up especially when concerns about costs, sample geometry and test practicality are raised.

Finishing and Polishing Procedures and Glaze Application on Physical Properties of a Fine-Structure Feldspathic Ceramic.

The aim of this study was to verify the effect of finishing and polishing procedures and glaze application on biaxial strength and surface properties of milled feldspathic ceramic blocks. Forty disc-shaped samples (14 mm diameter, 1.2 mm thickness) were divided in four groups (n = 10): C (control): no finishing and polishing; FP: finishing and polishing; G: glaze; and GFP: finishing and polishing + glaze. The specimens were subject to surface gloss (glossmeter) and roughness (profilometer) tests followed by biaxial flexural strength (universal testing machine) and Vickers hardness (microhardness tester) tests. The surface morphological analysis was performed by scanning electron microscopy (n = 3). Data were submitted to normality tests with Shapiro-Wilk, and one-way ANOVA followed by Tukey's post hoc test (α = 0.05). Group C showed the lowest gloss. For the hardness test, groups C, FP, and GFP obtained the highest values without significant differences between them. Regarding the biaxial strength test, group C showed the lowest mean value. Both finishing and polishing methods (FP and GFP) showed surface properties similar or better than the control, and with higher biaxial strength.

Biaxial tensile testing system for measuring mechanical properties of both sides of biological tissues

The aortic wall exhibits a unique elastic behavior, periodically expanding in aortic diameter by approximately 10% during heartbeats. This elastic behavior of the aortic wall relies on the distinct yet interacting mechanical properties of its three layers: intima, media, and adventitia. Aortic aneurysms develop as a result of multifactorial remodeling influenced by mechanical vulnerability of the aortic wall. Therefore, investigating the mechanical response of the aneurysmal wall, in conjunction with changes in microstructural parameters on both the intimal and adventitial sides, may offer valuable insights into the mechanisms of aortic aneurysm development or rupture. This study aimed to develop a biaxial tensile testing system to measure the mechanical properties of both sides of the tissue to gain insights concerning the interactions in anisotropic layered tissue. The biaxial tensile test set-up consisted of four motors, four cameras, four load cells, and a toggle switch. Porcine ascending aortas were chosen as the test subject. Graphite particles with diameters of approximately 5–11 [μm] were randomly applied to both sides of the aorta. Strain measurements were obtained using the stereo digital-image correlation method. Because stretching a rectangular specimen with a thread inevitably concentrates and localizes stress, to reduce this effect the specimen's shape was investigated using finite element analysis.The finite element analysis showed that a cross-shaped specimen with diagonally cut edges would be suitable. Therefore, we prepared specimens with this novel shape. This test system showed that mechanical response of the aortic tissue was significantly different between the intimal and adventitial side in the high-strain range, due to the disruption of collagen fibers. The adventitia side exhibited a smaller elastic modulus than the intimal side, accompanied by disruption of collagen fibers in the adventitia, which were more pronounced in the longitudinal direction. In contrast, in the mid-strain range, the elastic modulus did not differ between the intimal and adventitial sides, irrespective of longitudinal or circumferential direction, and collagen fibers were not disrupted but elongated.A biaxial tensile test system, which measures the mechanical properties of both sides of biological tissues and the shape of the specimen for reducing the concentration of stress at the chuck region, was developed in this study. The biaxial tensile testing system developed here is useful for better understanding the influences of mechanical loads and tissue degeneration on anisotropic, layered biological tissues.

Production and mechanical characterization of Titanium Carbide ISOL target disks fabricated by direct ink writing

Titanium carbide boasts a large variety of high-temperature applications from aerospace to electronics and is also employed as Isotope Separation On-Line target for the production of Radioactive Ion Beams, which are employed in numerous research and technological fields, ranging from nuclear physics to medical applications. High working temperature, open and tailored porosity and resistance to thermal stresses are fundamental characteristics for this kind of targets. In this work, an extrusion-based additive manufacturing technique (Direct Ink Writing) was used for the fabrication of complex three-dimensional macro-porous structures in the shape of disks with dimensions compatible for their use as targets. An ink containing a suspension of TiC powders with solid loading of 47.5 vol% was prepared and its rheological properties were investigated. Afterwards, single filaments with an average diameter of 0.36 mm were produced and characterized with four-point bending tests to determine the bulk material tensile strength and Young's modulus. TiC targets were then manufactured and their mechanical properties were characterized with the Ball on Three Balls approach, a biaxial flexural test suitable for disk-shaped samples. For both flexural tests, a Finite Element model was developed representatively reproducing the experimental results. The calculated tensile strength values for both filaments and disks were analyzed with Weibull's statistical approach to provide reference stress limit, corresponding to a survival probability of 99.9%.

Orthotropic multisurface model with damage for macromechanical analysis of masonry structures

A novel macromechanical model with damage for the analysis of masonry structures in-plane loaded is presented. The model accounts for the directional mechanical properties typically characterizing response of masonry with regular texture. Indeed, the real heterogeneous material is modeled as a fictitious homogenized medium with orthotropic elastic constitutive behavior along the masonry natural axes, identified as the parallel and normal directions to bed joints orientation. The different strength characteristics along each material axis are taken into account by properly defining a damage matrix, which accounts for failure mechanisms due to axial tensile and compressive states, as well as shear. A suitable criterion is introduced, resulting in a damage limit surface geometrically defined in the space of the damage associated variables by the intersection of two ellipsoids and an hyperboloid. The model is implemented into a finite element procedure where the mesh-dependency numerical issue is avoided by adopting a nonlocal integral formulation. Validation examples, involving simple uni-axial and bi-axial tests, as well as more complex loading conditions, are provided to prove the model performances at both material and structural scale.

Comparison of local and nonlocal regularization approaches in Eulerian-based finite element analyses

Finite element (FE) results might suffer from significant mesh dependency, especially when modeling shear bands in strain-softening soils. On the other hand, the shear bands in the field are generally thin. The computational costs might dramatically increase when modeling such thin shear bands, especially for large-scale problems, such as progressive landslides. To overcome these issues, FE analyses are generally performed with larger shear band thicknesses by adopting ‘softening scaling’ rules based on local and nonlocal (averaged) strains at the shear bands. The present study compares the performances of local and nonlocal approaches, with a specific focus on softening scaling and large deformation. Analyses are performed using a Eulerian-based FE program, which can model large strains in the shear band without numerical issues related to mesh distortion. Implementing strain-softening behavior in local and nonlocal methods, two idealized cases are simulated: (i) biaxial compression test, (ii) slope failure due to upslope surface loading. FE simulations show that the macroscopic response (i.e., load–displacement behavior) can be modeled using both local and nonlocal regularization techniques. Shear band thickness increases with the progress of shearing. In local analysis, mesh orientation has a considerable effect on shear band thickness. The existence of neighboring shear bands could affect nonlocal strain calculation and the simulation results.

Effect of battery fast cyclic charging on the mechanical and fracture behavior of the lithium-ion battery separator

The effect of cyclic fast charging on the mechanical and physicochemical properties of the lithium-ion battery separator is investigated. For that purpose, six battery pouch cells were cycled at 4C charge and 0.5C discharge rates for up to 400, 800, and 1600 cycles. Once the fast charging cycles were completed, the battery pouch cells were fully discharged and carefully disassembled. The physical and chemical microstructural properties of pristine and cycled separators were investigated using scanning electron micrographs (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Additionally, the mechanical behavior of the pristine and cycled separators was also investigated through uniaxial tensile and biaxial punch tests. While the XPS and FTIR analyses of the cycled separator surfaces did not reveal the presence of chemical degradation, the mechanical properties presented a decrease in toughness and ductility with an increased number of charging cycles. A thorough discussion of the possible degradation mechanisms of the cycled separator is provided by combining the results of our analysis and of those reported in the literature.