Uniaxial Stress-strain Curves Research Articles

Constitutive models and failure properties of fibrous tissues of carotid artery atheroma based on their uniaxial testing

To obtain an experimental background for the description of mechanical properties of fibrous tissues of carotid atheroma, a cohort of 141 specimens harvested from 44 patients during endarterectomies, were tested. Uniaxial stress–strain curves and ultimate stress and strain at rupture were recorded. With this cohort, the impact of the direction of load, presence of calcifications, specimen location, patient’s age and sex were investigated. A significant impact of sex was revealed for the stress–strain curves and ultimate strains. The response was significantly stiffer for females than for males but, in contrast to ultimate strain, the strength was not significantly different. The differences in strength between calcified and non-calcified atheromas have reached statistical significance in the female group. At most of the analysed stress levels, the loading direction was found significant for the male cohort which was also confirmed by large differences in ultimate strains. The representative uniaxial stress–strain curves (given by median values of strains at chosen stress levels) were fitted with an isotropic hyperelastic model for different groups specified by the investigated factors while the observed differences between circumferential and longitudinal direction were captured by an anisotropic hyperelastic model. The obtained results should be valid also for the tissue of the fibrous cap, the rupture of which is to be predicted in clinics using computational modelling because it may induce arterial thrombosis and consequently a brain stroke.

Inverse Parameter Identification for Hyperelastic Model of a Polyurea.

An inverse procedure was proposed to identify the material parameters of polyurea materials. In this procedure, a polynomial hyperelastic model was chosen as the constitutive model. Both uniaxial tension and compression tests were performed for a polyurea. An iterative inverse method was presented to identify parameters for the tensile performance of the polyurea. This method adjusts parameters iteratively to achieve a good agreement between tensile forces from the tension test and its finite element (FE) model. A response surface-based inverse method was presented to identify parameters for the compression performance of the polyurea. This method constructs a radial basis function (RBF)-based response surface model for the error between compressive forces from the compression test and its FE model, and it employs the genetic algorithm to minimize the error. With the use of the two inverse methods, two sets of parameters were obtained. Then, a complete identified uniaxial stress–strain curve for both tensile and compressive deformations was obtained with the two sets of parameters. Fitting this curve with the constitutive equation gave the final material parameters. The present inverse procedure can simplify experimental configurations and consider effects of friction in compression tests. Moreover, it produces material parameters that can appropriately characterize both tensile and compressive behaviors of the polyurea.

Realistic morphology-based Representative Volume Elements for dual-phase steels

We present a framework for the digitization of Dual-Phase (DP) steel microstructures into three-dimensional Representative Volume Elements (RVEs). Using a stack of microscopy images 6-μm high, separated by approximately 0.3 μm, in a microstructure analysis software, we obtain solid models, and subsequently finite element meshes of RVEs for three DP steels with distinct microstructures. No approximations with regards to the shape, size, and distribution of the second phase particles are required. A comprehensive mean-field model due to (Allain et al., 2015) obtains flow curves for the martensite and ferrite; ferrite grain size, average martensite island size, and steel composition are the inputs. It bears emphasis that no additional parameter adjustments to the flow curves was required. The finite element model was solved with an implicit integration scheme to obtain uni-axial stress–strain curves that agree with the experimental curves to within 8%. We use our framework to propose some guidelines for the development of RVEs. We also show that the plastic strain between the martensite islands, at the onset of necking, is approximately 2.5-3 times the global necking strain. Furthermore, we make a case for the iso-work assumption made in one-dimensional mean-field models that treat DP steel as a two phase composite.

Microstructure and modeling of uniaxial mechanical properties of Polyethersulfone nanocomposite ultrafiltration membranes

Polyethersulfone (PES) nanocomposite membranes are some of the emerging ultrafiltration technologies that have promising applications in gas separation and wastewater treatment due to their unique microporous structure and cheapness. However, the effect of nanofiller additives on their mechanical and viscoelastic properties is still missing and these fundamentals should be known to designers and manufacturers for potential upscaling. In this context, this research aims to study the uniaxial mechanical behaviors of PES membranes and their nanocomposites (CNTs/PES and Graphene/PES), and then to model their mechanical characteristics based on the results of mechanical experiments. In order to achieve that, four batches from CNTs/PES and Graphene/PES nanocomposite membranes with different concentrations of nanofillers (0.01-0.04 wt.%) were prepared using a solution casting method and a tape casting process. Also, another neat PES batch was prepared for comparison. The pore topology of the synthesized membranes was observed using SEM. Afterwards, the mechanical tensile specimens were cut from the synthesized membranes and tested according to standard ASTM 638M-3 using a uniaxial universal testing machine. Finally, a nonlinear uniaxial stress-strain model was built to simulate the mechanical performance of the fabricated membranes using the generalized Maxwell model. The results showed that the mechanical properties of the membranes were reduced significantly by additives (up to 26% for CNTs and 57% for GA compared with neat batch) because of the changes in the pore topology (orientation, size, and distribution) of the prepared membranes,whereas the modeling results showed that the constitutive model is valid for deducing the uniaxial stress-strain curves of PES membrane and its nanocomposites membranes with a high predictability and average deviation estimated at 0.715% (PES), 0.302% for CNTs/PES and 0.164% for GA/PES membranes.

Experimental and numerical analysis of compression and bending strength of old wood reinforced with CFRP strips

The reinforcement and repair of historical wooden structures is very important because they reflect the socio-economic structure and architectural construction techniques of the period it was built. In this study, carbon fiber-reinforced polymer (CFRP) strips were used to improve the mechanical behaviors of old wood (OW) samples that were damaged over time because of various environmental effects and biological factors. To determine the effect of reinforcement on the strength values of OW and new wood (NW) samples under bending and compression loads, CFRP strips were applied at tension surfaces of bending samples and around the perimeter of compression samples. The effect of reinforcement on mechanical properties of OW and NW samples was evaluated with a statistical analysis program. Moreover, the ductility and energy dissipation capacities of experimental samples was calculated from the load-deflection curve obtained under bending loading. Reinforcement with CFRP has significantly improved the mechanical strength and stiffness of OW samples. The bending strength values increased 28%, 34% and 59% for new wood (NW), reinforced old wood (FROW) and reinforced new wood (FRNW) with respect to the non-reinforced OW, respectively. The modulus of elasticity values of NW, FROW and FRNW were 15%, 19% and 34% higher than OW, respectively. The 3-dimensional numerical model was developed and validated by experimental tests carried out on wood samples with and without reinforcement arrangements. Wood behaviors were modeled using uniaxial stress-strain curves. In numerical analysis, load-deflection curves, equivalent stresses and normal stresses of the beams were obtained. A good correlation was obtained between numerical and experimental results.

Finite Element Analysis on Steel-Concrete Composite Beams Considering the Bond-Slip Effect on the Interface

In order to accurately simulate the bond-slip performance of steel-concrete composite beams, a trilinear stress-strain relation model was adopted to simulate the mechanical properties of steel. A uniaxial stress-strain relation curve was used to study the nonlinear mechanical behaviors of concrete. The resisting shear effects of studs and concrete in the bonding area were equivalent to nonlinear springs. Based on the energy principle, a calculation method of the interfacial bond stiffness of steel-concrete composite beams was proposed and the interfacial bond-slip constitutive relation of steel-concrete composite beams was given. Based on it, the three-dimensional finite element analysis model of steel-concrete composite beams was established by the finite element analysis software ANSYS, and the numerical simulations of existing push-out tests of composite beams were performed. By comparison, it can be seen that the results from finite element analysis in this paper are close to the experimental ones. It indicated that the finite element analysis model can accurately simulate the bond-slip action of the interface, and this model can be applied to the numerical calculation and analysis of steel-concrete composite beams.

Dynamic crystal plasticity modeling of single crystal tantalum and validation using Taylor cylinder impact tests

In this work, we extend a dislocation-density based constitutive theory for the dynamic thermomechanical behavior of crystals to body centered cubic (BCC) tantalum. Strain rate and temperature dependence of the slip resistance in the model is incorporated via an expression for the state-dependent instantaneous saturation dislocation density and a dynamic recovery fraction that affects the rate of generation of immobile dislocation density. Crystallographic slip along 111 on the {110} or {112} planes as well as their combination are examined. The Schmid stress serves as the driving force for dislocation motion and the twinning/anti-twinning sense of slip on {112} planes is accounted for by introduction of Peierls stress that depends upon this sense. The model parameters are calibrated using a two-stage Bayesian approach against experimentally generated uniaxial stress-strain compression curves at quasi-static and high strain rates over a range of temperatures. Velocity-time histories from single crystal flyer plate impact experiments were also used to parameterize this model. The calibrated model was applied to simulate previous Taylor cylinder impact experiments. Our results show that the model must include slip on {110} and {112} planes and also account for the twinning versus anti-twinning sense of slip on {112} planes, to appropriately represent the orientation dependence of the flow stress and match the deformed geometry of the single crystal Taylor cylinders.

Plastic temperature-dependent constitutive modeling of pure aluminum diaphragms at large strains by using bulge test

A plastic temperature-dependent constitutive model is developed for 0.05 mm thickness pure aluminum diaphragms at large strains by using bulge test method. Rupture strain of the material is recorded below two percent according to tensile tests. In order to achieve the material behavior at larger strains, an own bulge test apparatus is used to extract equi-biaxial stress–strain curves at different temperatures, i.e. from room to 150 °C. Effective stress–strain behavior is then computed via a transformation scheme using the plastic work definition as well as the room temperature uniaxial stress–strain curve. It is illustrated that the Johnson–Cook constitutive model is not able to capture this stress–strain behavior. Thus, a modified Johnson–Cook model is developed in which the strain hardening is assumed to be temperature-dependent accompanying by a novel thermal softening relation. Using the Least-square method as well as the Ant colony optimization algorithm, the material parameters of the both models are calculated. It is depicted that the new model follows the material behavior more precisely than the Johnson–Cook model. The new model is then numerically implemented into finite element software via a user subroutine. In order to compare the accuracy of both models in capturing the hot bi-axial deformation of pure aluminum, an experiment is performed and numerically simulated.

A Simplified Uniaxial Stress-strain Curve of Concrete and Its Application in Numerical Simulation

Detennining the constitutive model is a key procedure in numerical simulation of concrete structures. The uniaxial stress-strain curve is important information to determine the concrete constitutive model. This paper provided a simplified stress-strain curve of concrete that can be used in simulation. The comparison between Chinese Code and the simplified curve shows that the simplified curve of uniaxial compression is close to the code value. Numerical simulation of concrete beams show that the simplified curve proposed has high computational efficiency and good convergence.

Mechanical properties and constitutive analyses of basalt fiber crumb rubber mortars in soft rock roadways

Uniaxial compressive stress-strain curves of several groups of basalt fiber crumb rubber mortars (BF-CRM) with different contents are tested. By comparing with the GZH model, the improved values of the parameters of the BF-CRM constitutive model based on the GZH model are obtained. Then, taking the supporting scheme of main substation of the mine as the background, using FLAC3D to simulate the roadway support, using BF-CRM to replace the ordinary mortars in the original support, and combining with the triaxial compression test of different confining pressure, the application effect of BF-CRM in roadways support is studied and analyzed.

Characterization of plastically compressible solids via spherical indentation

The response in spherical indentation is used to identify material properties for plastically compressible materials with presumed known elastic properties. The materials are assumed to be characterized by a Deshpande–Fleck constitutive relation (Deshpande and Fleck, 2000). The indentation force versus indentation depth responses and the residual surface profiles (the surface profiles after unloading) are calculated for two sets of material parameters. These are regarded as the “experimental” input materials. The constitutive parameters for these two materials are identified using the Bayesian-type statistical approach of Zhang et al. (2019) both for noise-free and for noise-contaminated data. The uniaxial stress–strain responses obtained from the spherical indentation responses are good approximations of those of the “experimental” input materials, particularly if surface profile data is used, but the quality of the approximation decreases with increasing noise amplitude. Plastic compressibility is found to have a relatively small effect on the correction factor β in the Oliver–Pharr relation (Oliver and Pharr, 2004) between the unloading slope and the effective (or reduced) elastic modulus. The indentation response of the plastically compressible materials can be well-represented by a nearly incompressible plastic constitutive relation but the inferred uniaxial stress–strain response is a poor representation of the “experimental” material uniaxial stress–strain response. The predicted residual surface profile is less dependent on the assumed elastic constant values than is the indentation force versus indentation depth response. The indentation force versus indentation depth responses in spherical indentation for three materials with very different uniaxial stress–strain curves are found to be indistinguishable if the indentation depth is sufficiently small but are distinguishable if the indentation depth is sufficiently large.

A mechanical relation model for biaxial tension of nanofibrous membrane

It is important to evaluate the mechanical biocompatibility of nanofibrous membranes used in tissue engineering. This investigation proposed a modeling analysis to predict the biaxial behavior of randomly oriented nanofibrous membranes. An electrospinning process prepared poly(ε-caprolactone) nanofibers. The uniaxial stress–strain curve of a single nanofiber and the biaxial stress–strain curves of the membranes were experimentally obtained. The applicability of the analytical model was verified by the comparison between modeling prediction and experimental data. Experimental stress was lower than the predicted stress until large plastic deformation occurred because of structural imperfections, prestress, and the stretch-induced orientation in the membranes.

Estimation of Texture-Dependent Stress-Strain Curve and <i>r</i>-Value of Aluminum Alloy Sheet Using Deep Learning

The deformation of an aluminum alloy sheet is affected by its underlying crystallographic texture and has been extensively studied using the crystal plasticity finite element method (CPFEM). Numerical material test based on the CPFEM enables the quantitative estimation of the stress-strain curve and Lankford value (r-value), which depend upon the texture of aluminum alloy sheets. However, the application of CPFEM-based numerical material test to the optimization of aluminum alloy texture is computationally expensive. In this paper, we propose a method for rapidly estimating the stress-strain curves and r-values of aluminum alloy sheets using deep learning with a neural network. We train the neural network with the synthetic crystallographic texture and stress-strain curves calculated through the numerical material tests. To capture the features of synthetic texture from a {111} pole-figure image, the neural network incorporates a convolution neural network. Using the trained neural network, we estimate the uniaxial stress-strain curve and in-plane anisotropy of the r-value for various textures that contain Cube and S components. The results indicate that the application of a neural network trained with the results of numerical material test is a promising method for rapidly estimating the deformation of aluminum alloy sheets.

Correlation of Measured Load-Displacement Curves in Small Punch Tests with Tensile Stress-Strain Curves

The Small Punch Test (SPT) has demonstrated tremendous potential for high throughput evaluation of mechanical response of metal sheets. However, its application has thus far been limited to the estimation of plastic material properties such as yield strength and ultimate tensile strength. This paper demonstrates new analysis protocols for extracting the uniaxial stress-strain curves from the SPT measured load-displacement curves. This is accomplished by first establishing a correlation between the SPT measurements and corresponding finite element (FE) simulations that take as input the uniaxial stress-strain response of the material. After establishing this correlation, it is shown that the correlation can be inverted to estimate the uniaxial stress-strain response from the SPT load-displacement measurement on a new material sample.

Fiber splay precludes the direct identification of ligament material properties: Implications for ACL graft selection

Anterior cruciate ligament (ACL) injuries typically require surgical reconstruction to restore adequate knee stability. The middle third of an injured patient’s patellar tendon (PT) is a commonly used graft for ACL reconstruction. However, many clinicians and researchers question whether it is the best option, as several studies have suggested that it is a stiffer material than the ACL. Still, there is little to no consensus on even the most basic material property of ligaments/tendons: the tangent modulus in the fiber direction, or slope of the linear portion of the uniaxial stress–strain curve. In this study, we investigate the effect of fiber splay (the tendency of collagen fibers to spread out near the enthesis) on the apparent tangent modulus. Using a simplified theoretical model, we establish a quantity we call the splay ratio, which describes the relationship between splay geometry and the apparent tangent modulus. We then more rigorously investigate the effect of the splay ratio on the apparent tangent modulus of the ovine PT and anteromedial and posterolateral regions of the ACL using experimental and computational methods. Both approaches confirmed that splay geometry significantly affects the apparent material behavior. Because true material properties are independent of geometry, we conclude that the macroscopic response of ligaments and tendons is not sufficient for the characterization of their material properties, but rather is reflective of both material and structural properties. We further conclude that the PT is probably not a stiffer material than ACL, but that the PT graft is likely a stiffer structure than either ACL region.

Evaluation of high strength steels fracture based on uniaxial stress-strain curves

Predicting the ultimate capacity of components made of high strength steel (HSS) is a numerically challenging task. The fracture performance of HSS from different steel grades, producers, and manufacturing processes (rolling, cold forming, etc.) varies greatly. It is costly to conduct a series of experiments for each typical HSS structural component to identify the parameters of the fracture model. An attempt is made to evaluate the fracture material properties based only onthestandardizeduniaxial stress-strain curve. The uncoupled fracture model was implemented through a user subroutine VUMAT (ABAQUS) to evaluate theductilefracture of HSS, where a rate-independent non-linear isotropic J2 hardening model is used in combination with a separate Hosford-Coulomb fracture model. The detailed procedure to identify the material parameters based on only the uniaxial stress-strain curve of steel grades S700 and S960 areprovidedfor the sake of illustration of possible applications. The proposed fracture model and identified parametersare validatedbased on the experimental results of the HSS plate with different hole sizes in the middle of the dog bone specimens.Besides, a desktop study of a singleK gap joint with β = 0.5 made of square hollow sections using S700 and S960 is used toillustrate a possible application of the fracture modelina simplified model of the structural joint.

Size Effect and Influence Factors of Asphalt Mixture Based on Particle Discrete Element

To explore the size effect of asphalt mixture, asphalt mastic asphalt mixture was taken as the research object, and the uniaxial compressive strength was used as the evaluation index. The applicability of the three size effect theories of Bazant, Carpinteri, and Weibull were evaluated, and the corresponding size effect law parameters were calculated. The critical dimensions and critical strength of the asphalt mixture were determined, and the effects of coarse aggregate properties, maximum nominal particle size, and loading rate on the size effect of asphalt mixture were analyzed. Results show that the asphalt mixture has an obvious size effect phenomenon, and the uniaxial compressive stress-strain curves of asphalt samples with different sizes have the characteristics of compaction stage, elastic stage, and transition from plastic deformation to failure stage. The uniaxial compressive strength of the asphalt mixture is negatively correlated with the sample size, and as the sample size increases, the strength reduction decreases gradually. With the increase in the elastic modulus of the coarse aggregate, the critical strength value increases continuously, and the critical dimension decreases. As the maximum nominal particle size increases, the critical dimension and critical strength increase gradually. With the increase in the loading rate, the critical strength continues to increase, and the critical dimension gradually decreases. The Bazant and Carpinteri size effect laws are more suitable for the analysis of the size effect of asphalt mixture, while the Weibull size effect law has a large error. When SMA is used as the pavement structural layer, the ratio S of the structural layer thickness to the maximum nominal particle size calculated by the Bazant size effect law is 2.6 to 3.5, and the S range calculated by the Carpinteri size effect law is 2.6 to 4.0.

Applying a combination of laboratory X-Ray diffraction and digital image correlation for recording uniaxial stress-strain curves in thin surface layers

By combining laboratory-based x-ray diffraction stress analysis with optical digital image correlation recorded in-situ during tensile loading, a new methodology has been developed to obtain for surface specific stress-strain curves. This novel methodology has been validated by comparing the reconstructed stress-strain curves from the x-ray diffraction/optical digital image correlation approach with stress-strain curves recorded using standard methods. The validated methodology enables now the recording of standard mechanical test data of altered surface layers, such as shot peened and machined surfaces or from proton-irradiated samples where the irradiated layer is limited to a depth of 10 s of microns.

Influence of Assumed Strain Hardening Relation on Plastic Stress-Strain Response Identification From Conical Indentation

Abstract Instrumented indentation tests provide an attractive means for obtaining data to characterize the plastic response of engineering materials. One difficulty in doing this is that the relation between the measured indentation force versus indentation depth response and the plastic stress-strain response is not unique. Materials with very different uniaxial stress-strain curves can give essentially identical curves of indentation force versus indentation depth. Zhang et al. (2019, “Identification of Plastic Properties From Conical Indentation Using a Bayesian-Type Statistical Approach,” ASME J. Appl. Mech., 86, p. 011002) numerically generated “experimental” conical indentation data and showed that using surface profile data and indentation force versus indentation depth data together with a Bayesian-type statistical analysis permitted the uniaxial plastic stress-strain response to be identified even for materials with indistinguishable indentation force versus indentation depth curves. The same form of hardening relation was used in the identification process as was used to generate the “experimental” data. Generally, a variety of power law expressions have been used to characterize the uniaxial plastic stress-strain response of engineering materials, and, of course, the form that gives the best fit for a material is not known a priori. Here, we use the same Bayesian statistics-based analysis but consider four characterizations of the plastic uniaxial stress-strain response and show that the identification of the hardening relation parameters and the associated uniaxial stress-strain response is not very sensitive to the form of the power law strain hardening relation chosen even with data that have significant noise.

A biostable, anti-fouling zwitterionic polyurethane-urea based on PDMS for use in blood-contacting medical devices.

Polydimethylsiloxane (PDMS) is commonly used in medical devices because it is non-toxic and stable against oxidative stress. Relatively high blood platelet adhesion and the need for chemical crosslinking through curing, however, limit its utility. In this research, a biostable PDMS-based polyurethane-urea bearing zwitterion sulfobetaine (PDMS-SB-UU) was synthesized for potential use in the fabrication or coating of blood-contacting devices, such as a conduits, artificial lungs, and microfluidic devices. The chemical structure and physical properties of synthesized PDMS-SB-UU were confirmed by 1H-nuclear magnetic resonance (1H-NMR), X-ray diffraction (XRD), and uniaxial stress-strain curve. In vitro stability of PDMS-SB-UU was confirmed against lipase and 30% H2O2 for 8 weeks, and PDMS-SB-UU demonstrated significantly higher resistance to fibrinogen adsorption and platelet deposition compared to control PDMS. Moreover, PDMS-SB-UU showed a lack of hemolysis and cytotoxicity with whole ovine blood and rat vascular smooth muscle cells (rSMCs), respectively. The PDMS-SB-UU was successfully processed into small-diameter (0.80 ± 0.05 mm) conduits by electrospinning and coated onto PDMS- and polypropylene-based blood-contacting biomaterials due to its unique physicochemical characteristics from its soft- and hard- segments.