Uniaxial Tension Compression Tests Research Articles

Crystal plasticity finite element simulations on extruded Mg-10Gd rod with texture gradient

The mechanical properties of an extruded Mg-10Gd sample, specifically designed for vascular stents, are crucial for predicting its behavior under service conditions. Achieving homogeneous stresses in the hoop direction, essential for characterizing vascular stents, poses challenges in experimental testing based on standard specimens featuring a reduced cross section. This study utilizes an elasto-visco-plastic self-consistent polycrystal model (ΔEVPSC) with the predominant twinning reorientation (PTR) scheme as a numerical tool, offering an alternative to mechanical testing. For verification, various mechanical experiments, such as uniaxial tension, compression, notched-bar tension, three-point bending, and C-ring compression tests, were conducted. The resulting force vs. displacement curves and textures were then compared with those based on the ΔEVPSC model. The computational model's significance is highlighted by simulation results demonstrating that the differential hardening along with a weak strength differential effect observed in the Mg-10Gd sample is a result of the interplay between micromechanical deformation mechanisms and deformation-induced texture evolution. Furthermore, the study highlights that incorporating the axisymmetric texture from the as-received material incorporating the measured texture gradient significantly improves predictive accuracy on the strength in the hoop direction. Ultimately, the findings suggest that the ΔEVPSC model can effectively predict the mechanical behavior resulting from loading scenarios that are impossible to realize experimentally, emphasizing its valuable contribution as a digital twin.

Parameter identification of Yoshida–Uemori combined hardening model by using a variable step size firefly algorithm

Abstract The material behavior under cyclic loading is more complex than under monotonic loading and the usage of the sophisticated constitutive models is required to accurately define the elastoplastic behaviors of the advanced high-strength steels and aluminum alloys. These models involve the numerous material parameters that are determined from cyclic tests and accurate calibration of the variables has a great influence on the description of the material response. Therefore, the development of a precise and robust identification method is needed to obtain reliable results. In this study, a systematic methodology depending upon the firefly algorithm (FA) with variable step size has been developed and Yoshida–Uemori combined hardening model parameters of a dual-phase steel (DP980) and an aluminum alloy (AA6XXX-T4) are determined. The identified parameters are verified based on comparisons between the finite element simulations of the cyclic uniaxial tension-compression tests and experimental data and also the search performance of the variable FA is evaluated by comparing it with the standard FA. It is seen from these comparisons that variable FA can easily find and rapidly converge to the global optimum solutions.

Micro–macro approach of anisotropic damage: A semi-analytical constitutive model of porous cracked rock

A semi-analytical constitutive model of a porous cracked rock is proposed based on the micro–macro approach within a thermodynamic framework. The representative volume element (RVE) of a porous cracked rock is divided into two subproblems, P1 and P2. The porosity evolution equation of a spherical pore is proposed for P1, whereas P2 is an inelastic problem containing numerous anisotropic penny-shaped cracks. First, the relationship between microscopic and macroscopic strains is established through homogenization. This relationship is introduced into the macroscopic free energy equation. A crack propagation criterion based on the Griffith release rate is proposed, and the evolution equations of the shear and tensile crack densities are proposed based on the surface energy function. Subsequently, the Gaussian numerical integration method is used to obtain a semi-analytical explicit expression of the macroscopic stiffness tensor. Finally, based on the proposed crack propagation criterion, a strength-prediction method is developed. A series of uniaxial and triaxial experimental data for different rocks from other references is used to validate the proposed constitutive model and strength prediction method. The results obtained using the proposed model agree well with the experimental curves obtained from uniaxial tension and triaxial compression tests performed on different rocks. The macroscopic mechanical behavior and evolution of microscopic parameters for different rocks with an increase in confining pressure are effectively demonstrated by the proposed model. Strength prediction method can accurately describe the failure strength of different rocks. Furthermore, a sensibility analysis of model parameters revealed that initial porosity e0 and dilation coefficient ζ have a deteriorating effect on the failure strength, and material constant η has an enhancing effect on the failure strength.

Tensile and Compressive Mechanical Behaviour of Human Blood Clot Analogues

Endovascular thrombectomy procedures are significantly influenced by the mechanical response of thrombi to the multi-axial loading imposed during retrieval. Compression tests are commonly used to determine compressive ex vivo thrombus and clot analogue stiffness. However, there is a shortage of data in tension. This study compares the tensile and compressive response of clot analogues made from the blood of healthy human donors in a range of compositions. Citrated whole blood was collected from six healthy human donors. Contracted and non-contracted fibrin clots, whole blood clots and clots reconstructed with a range of red blood cell (RBC) volumetric concentrations (5–80%) were prepared under static conditions. Both uniaxial tension and unconfined compression tests were performed using custom-built setups. Approximately linear nominal stress–strain profiles were found under tension, while strong strain-stiffening profiles were observed under compression. Low- and high-strain stiffness values were acquired by applying a linear fit to the initial and final 10% of the nominal stress–strain curves. Tensile stiffness values were approximately 15 times higher than low-strain compressive stiffness and 40 times lower than high-strain compressive stiffness values. Tensile stiffness decreased with an increasing RBC volume in the blood mixture. In contrast, high-strain compressive stiffness values increased from 0 to 10%, followed by a decrease from 20 to 80% RBC volumes. Furthermore, inter-donor differences were observed with up to 50% variation in the stiffness of whole blood clot analogues prepared in the same manner between healthy human donors.

An advanced constitutive model for transversely isotropic rock - Evaluation of two different regularization approaches

The mathematical description of the material behavior of rock is a demanding task in engineering practice. Rock is classified as a frictional cohesive material characterized by highly nonlinear mechanical behavior with irreversible deformation, strain hardening, strain softening and degradation of stiffness. In addition, depending on the origin of a particular rock type, the orientation of minerals and grains as well as the formation of stratification planes lead to inherent anisotropic behavior. Especially in stratified rock types like shales or phyllites, often the special case of transversely isotropic material behavior is encountered. In a previous work, a novel continuum-based material model for describing both, the highly nonlinear and transversely isotropic material behavior of rock, denoted as TI-RDP model, was presented. By means of the linear mapping of the Cauchy stress tensor into a fictitious isotropic configuration, an established isotropic damage plasticity model for rock was extended. In this contribution two different regularization approaches, which are well established for isotropic models, i.e., the mesh-adjusted softening modulus and the implicit gradient-enhancement, are adopted for the TI-RDP model. Based on uniaxial tension and triaxial compression tests considering different orientations of the principal material directions with respect to the direction of axial loading, their capabilities are assessed in terms of predicting the direction-dependent mechanical behavior in a mesh-insensitive manner.

Phase-field modeling of fracture in high performance concrete during low-cycle fatigue: Numerical calibration and experimental validation

The development of an elasto-plastic phase-field model is presented which is able to predict nonlinear behavior of high performance concrete (HPC) during low-cycle fatigue. An elasto-plastic damage model which follows the Drucker–Prager yield criterion is formulated. For the modeling of unsymmetric tension–compression behavior of HPC two different continuous stepwise linearly approximated degradation functions for HPC in tension and in compression are used. The experimental three-point bending tests at low-cycle using notched beams of pure HPC are performed. Load–CMOD (crack mouth opening displacement) curves are plotted using the measured experimental data and residual stiffness–CMOD curves are calculated using these experimental Load–CMOD curves. The data used for the interpolation of degradation functions are calibrated using the experimental results for three-point bending tests. For that purpose the uniaxial tension and uniaxial compression tests and three-point bending beam test for HPC are simulated numerically. The accuracy of the proposed numerical model using the presented integration algorithm is verified by comparing the degradation of stiffness in numerical and experimental results.

Analytical Model for Failure Strength of Brittle Rocks under Triaxial Compression and Triaxial Extension

Rocks exhibit different failure strengths under triaxial compression and extension. The understanding and quantification of their relationship provide theoretical and practical benefits. Conventional Mohr-type criteria cannot distinguish rock failure strengths under triaxial compression and extension. To overcome this limitation, we present an analytical model based on Mohr failure theory to describe the relationship between the rock failure strengths under triaxial compression and extension in a Mohr plane. Our analytical model indicates that rock failure criteria under both triaxial compression and extension can be expressed in power-law forms. The corresponding strength magnitude and Mohr envelope curvature parameters are analytically determined using measured rock properties from uniaxial tension, uniaxial compression, and equibiaxial compression tests. This model is validated using experimental data of five rock types: granite, marble, basalt, dolomite, and sandstone. Compared with four well-known failure criteria, the proposed model demonstrates the ability to predict the failure strengths of rocks under both triaxial compression and extension.

Elucidation of mechanical characteristics of Xenopus laevis embryos by seamless uniaxial tension-compression test

Elucidation of mechanical characteristics of Xenopus laevis embryos by seamless uniaxial tension-compression test

Tailoring of functionally graded hyperelastic materials via grayscale mask stereolithography 3D printing

Photopolymerization-based additive manufacturing methods like stereolithography and digital light processing only allow typically the monolithic fabrication of structures made from a single material. To overcome this limitation, grayscale digital light processing has been proposed for 3D printing of functionally graded materials. Here, this concept is extended to grayscale masked stereolithography (MSLA) printing using a LED light source and a LCD photomask to control the degree of photopolymerization of a UV-curable resin by varying grayscale pixels and thus light intensities. In this scale, tailorable hyperelastic material properties and functionally graded structures for finite deformations are realized. In this paper, the dependency of the resulting material properties on the parameters of the grayscale MSLA process is investigated and a grayscale-dependent hyperelastic material model is formulated. This parametric hyperelastic material model is fitted to the experiments and validated against experimental results for uniaxial tension and uniaxial compression tests. Then, functionally graded structures with tailored mechanical properties at finite deformations are designed and fabricated using grayscale MSLA printing. The hyperelastic material model is validated with experimental results for different geometries, showing good agreement between experimental tests and numerical calculations.

Mechanical characterization of grid-reinforced interfaces within rehabilitated bituminous layers

The installation of a layer of grid, as an interlayer between bituminous layers, enhances the mechanical performance of the entire system under repetitive action of traffic loads, typically by increasing the tensile and shear strength at the interface level. At the same time, this mechanical improvement is accompanied by changes in mechanical responses of the system in terms of axial stiffness and structural integrity, which needs to be well defined in performance-based design methods. This research was dedicated to know how to characterize the mechanical alterations at the reinforced interface of bituminous layers from different mixtures, concerning axial stiffness and adhesion quality through a comparative analysis with corresponding unreinforced cases. In doing so, a new configuration of extensometers in the tension–compression complex modulus test was suggested to elucidate the changes in structural responses at different heights relative to the interface. Furthermore, a uniaxial tension–compression test was utilized to evaluate the adhesion bond at the interface level. The results demonstrated that the proposed methodology of doing complex modulus test could be employed as a practical tool to compare the rheological behavior of the interfaces with dissimilar conditions. In addition, the 2 Springs, 2 Parabolic creep elements, and 1 Dashpot (2S2P1D) model could be reliably employed to predict the mechanical behavior of any type of interface at high frequencies or low temperatures. Also, the strain amplitude, determined at one million loading cycles, i.e. ε6, provided a proper indication of the adhesion bond in reinforced and unreinforced systems at the interface level under cyclic loading.

Swage autofrettage FEA incorporating a user function to model actual Bauschinger effect

An ‘exemplar’ Finite Element Analysis (FEA) solution for swage autofrettage (SA) incorporating Bauschinger effect (BE) for a real steel (A723) is presented. This is derived via a new user programmable function (UPF). Datum geometries for tube and swage were selected in order to permit comparison with previous work.The FEA UPF solution methodology was developed and validated to demonstrate that a 3D analysis will fully replicate a uniaxial tension-compression test on a real material (A723 steel) exhibiting BE, designated UPF(U).A refined formulation designated UPF(S) was then used to obtain a solution for the full 3D axisymmetric SA process. It is first applied to an idealized (BKIN) material; to permit direct comparison with two existing BKIN SA solutions. Finally the UPF(S) formulation is used to obtain a solution for full 3D SA applied to a standard steel (A723) whilst incorporating BE during unloading.The near-bore BE SA solution is compared to an equivalent BE hydraulic autofrettage (HA) solution. Near-bore SA hoop residual stresses are shown to be more compressive and deeper than HA. Conversely SA produces tensile axial stresses, whereas HA generates compression. Finally, it is shown that a subsequent material removal process, applied to the SA tube, may significantly improve near-bore stress profiles.

A flexible porous chiral auxetic tracheal stent with ciliated epithelium

Tracheal stent placement is a principal treatment for tracheobronchial stenosis, but complications such as mucus plugging, secondary stenosis, migration, and strong foreign body sensation remain unavoidable challenges. In this study, we designed a flexible porous chiral tracheal stent intended to reduce or overcome these complications. The stent was innovatively designed with a flexible tetrachiral and anti-tetrachiral hybrid structure as the frame and hollows filled with porous silicone sponge. Detailed finite element analysis (FEA) showed that the designed frame can maintain a Poisson's ratio that is negative or close to zero at up to 50% tensile strain. This contributes to improved airway ventilation and better resistance to migration during physiological activities such as respiration and neck movement. The preparation process combined indirect 3D printing with gas foaming and particulate leaching methods to efficiently fabricate the stent. The stent was then subjected to uniaxial tension and local radial compression tests, which indicated that it not only has the same desirable auxetic performance but also has flexibility similar to the native trachea. The porous sponge facilitated the adhesion of cells, allowed nutrient diffusion, and would prevent the ingrowth of granulation tissue. Furthermore, a ciliated tracheal epithelium similar to that of the native trachea was differentiated from normal human bronchial primary epithelial cells on the internal wall of the stent under air-liquid interface conditions. These results suggest that the designed stent has the potential for application in the treatment of tracheobronchial stenosis.

An enhanced damage plasticity model for predicting the cyclic behavior of plain concrete under multiaxial loading conditions

Some of the current concrete damage plasticity models in the literature employ a single damage variable for both the tension and compression regimes, while a few more advanced models employ two damage variables. Models with a single variable have an inherent difficulty in accounting for the damage accrued due to tensile and compressive actions in appropriately different manners, and their mutual dependencies. In the current models that adopt two damage variables, the independence of these damage variables during cyclic loading results in the failure to capture the effects of tensile damage on the compressive behavior of concrete and vice-versa. This study presents a cyclic model established by extending an existing monotonic constitutive model. The model describes the cyclic behavior of concrete under multiaxial loading conditions and considers the influence of tensile/compressive damage on the compressive/tensile response. The proposed model, dubbed the enhanced concrete damage plasticity model (ECDPM), is an extension of an existing model that combines the theories of classical plasticity and continuum damage mechanics. Unlike most prior studies on models in the same category, the performance of the proposed ECDPM is evaluated using experimental data on concrete specimens at the material level obtained under cyclic multiaxial loading conditions including uniaxial tension and confined compression. The performance of the model is observed to be satisfactory. Furthermore, the superiority of ECDPM over three previously proposed constitutive models is demonstrated through comparisons with the results of a uniaxial tension-compression test and a virtual test.

Revisiting the lamellar globularization behavior of a two-phase titanium alloy from the perspective of deformation modes

Abstract The correlation between lamellar globularization and deformation modes during the primary hot processing of titanium alloy was evaluated by means of uniaxial compression, tension, torsion and plane strain compression tests. The microstructure evolution features and underlying globularization mechanisms were comparatively studied via Electron Backscattered Diffraction technique. Noticeable divergences of globularization response are captured in different deformation modes, especially for the globularized fractions and the critical strain. In the face of the strain applied is less than the critical globularization value (0.4−0.63) under uniaxial compression, the lamellae can be still globularized under tension or torsion deformation. But the growth rate of globularized fraction is more sluggish under tension than that under torsion deformation. The lamellae separation at early tension deformation preferentially occurs at junctions of lamellae without destroying Burgers Orientation relationship and significant orientation fluctuation. Shear deformation can facilitate the formation of intra-α boundaries and its distribution uniformity, which could make the lamellae grow up into globularized particles and improve the globularization heterogeneity. It is envisaged that the results obtained can provide guidance for the technology scheme and route design of primary hot working of titanium alloy aiming at the homogeneous equiaxed grains.

Study on the Mechanical Properties of Ice-Impregnated HTS Coils Formed Under Confining Pressure

Epoxy resins are commonly used to impregnate the High temperature superconducting (HTS) coils for mechanical reinforcement. However, performance degradation of the epoxy impregnated HTS coils is inevitable due to the different thermal expansion coefficients between the epoxy resin and the HTS tape. The ice impregnation technique of pulsed magnets was applied to HTS coils for the first time. But cracks were easily formed in ice during cooling process and the mechanical strength of ice was rarely studied at 77 K. To solve this problem, we introduced the technique of ice impregnation under confining pressure into HTS coils. In this paper, uniaxial tension test, compression test and crack detection test of ice were conducted in liquid nitrogen. And critical current of the HTS coil was also measured under confining pressure at 77 K. The experimental results showed that ice impregnated HTS coil under confining pressure did not have performance decay in critical current and the mechanical strength was significantly improved.

Validation of homogeneous anisotropic hardening model using non-linear strain path experiments

We conducted non-linear strain path experiments on a dual-phase steel-sheet sample. The first strain path in each of these experiments, called pre-strain, was always uniaxial tension in the direction transverse to the sheet (90° from the rolling direction). For this purpose, we clamped large tensile specimens in a suitable gripping system and deformed them to produce a sufficiently large area with a uniform strain distribution. We machined new specimens from this area, and we subjected them to different modes of deformation, namely uniaxial tension in different directions from the transverse direction, simple shear, and biaxial tension with different load ratios. In addition, we performed uniaxial tension-compression tests consisting of either one or three full cycles. We obtained the coefficients of a distortional plasticity model—the homogeneous anisotropic hardening (HAH) model—using an inverse analytical identification tool. First, we calibrated two sets of reverse loading coefficients using the tension-compression stress–strain curves obtained with either one or three full cycles. Then we used the 90° tension–45° tension and the 90° tension–0° simple-shear sequences to determine two sets of cross-loading coefficients. We compared the other independent experimental flow curves with simulations using the HAH model with combinations of the different sets of coefficients. These comparisons showed the influence of the selected input data on the calculations of the coefficients calibrated and demonstrated the advantages and limitations of the present HAH model.

Toughened carbon-fiber reinforced epoxy via isophorone diisocyanate amine surface modification

Surface modification of a carbon-fiber reinforced epoxy (CF/E) via isophorone diisocyanate amine (IDA) is investigated. The covalently bonded IDA, engendering a microscopically thin layer (2 μm–50 μm wide), is an exchange chemical reaction after topically spraying polyurea moieties (isocyanate and amine groups) to curing epoxy that is composed of amine and epoxide groups reacting for tc hours (h). Quasi-static nanoindentation, uniaxial tension and uniaxial compression tests reveal that the chemical bond feature of the tunable IDA surface, conceived at low tc, markedly improves damage tolerance in brittle CF/E by significantly supplementing the energy-release rate (fracture toughness). Compression tests revealed that energy absorption and deflection ductility of IDA-modified CF/E, i.e., C-IDA, and prepared at tc = 0 h, are two and five times greater relative to C-IDA at tc = 0.5 h. Tension tests revealed that energy absorption and deflection ductility of C-IDA at tc = 0 h are 150% and 50% greater than C-IDA at tc = 24 h. Micromechanical properties of the IDA reaction include a uniquely distributed reduced elastic modulus (Er), bounded by moduli of pure epoxy and pure polyurea (overspray). The results, in concert with atomic force microscopy (AFM) and non-negative matrix factorization (NMF) results, validate a link between IDA chemistry and mechanical energy transferability. Manifested as damage localization, fractograph analysis also confirms existence of the link, where bridging of individual damage events in CF/E is markedly reduced.

Springback Evaluation of Tailor Welded Blanks at V-die Bending made of DP Steels

This study presents the experimental results and the comparison of different analytical models for springback evaluation of bent thin sheets. Three types of advanced high strength steels (from the group of dual phase steels, namely DP600, DP800 and DP1000) and a mild steel (DC04) were used to investigate the sheet profile after rectangular V-die bending. Uniaxial tension-compression tests were also carried out formerly to lay the basis of the precise theoretical examinations. Striving to consider all possible circumstances, the change of the elastic modulus with the increase of the plastic strain, as well as plane strain state with the corresponding yield stress were assumed during the springback prediction. In certain cases, the effect of the sheet thickness variation was also taken into account. In many practical stampings, these variables can be at least partially neglected, but the presented models also can lead to poor accuracy, even though they are more complicated. According to our experiences, both the circular approximation and the moment-equilibrium based general formulae predict under the measured springback angles, but the punctuality can be developed by precise material behavior modelling. The phenomenological approach extended with fitting parameters gives the most accurate estimation obviously, but the physical meaning of the added parameters remain a question. The uncertainty is being more enhanced at the tailor-welded blanks (TWBs) where the interaction of the components should not be negligible as well, i.e. a subsequent variable, namely the distance from the weld line comes into the focus. Laser beam welding was applied to joint each DP steels to the mild steel component and then the sheets with different widths were bent perpendicular to the weld line. Due to the doubled effect on the deforming or restraining action of the different sides, the final shape and thus the curvature shift towards the weld line from the blank’s edge. It means that new viewpoints need to consider at the analytical springback evaluation of TWBs.

Mesomechanism of the dynamic tensile fracture and fragmentation behaviour of concrete with heterogeneous mesostructure

As a typical multi-phase material, due to its heterogeneous mesostructure, concrete exhibits complicated mechanical responses when subjected to high-rate loads. Considering concrete is much weaker in tension than in compression, it is of significance to investigate the mesomechanism of the dynamic tensile fracture behaviour of concrete under high-rate loading conditions. In this study, the meso-heterogeneity of concrete is considered by random mesostructure generation with efficient algorithm of Entrance block between A and B (E(A, B)). A 2D meso-scale model is developed by implementing a combined FDEM scheme with zero-thickness cohesive elements in ABAQUS software. The proposed model is validated by quasi-static uniaxial tension and uniaxial compression tests as well as dynamic Brazilian tensile split Hopkinson pressure bar (SHPB) test and then used in a series of Brazilian tensile SHPB tests to investigate the influences of the loading rate, aggregate area fraction and the mechanical properties of the interfacial transition zone (ITZ) on dynamic tensile behaviour of concrete. The numerical results indicate that the dynamic tensile strength increases with increasing loading rate and the fragmentation experiences a transition from parse fracturing to dramatic pulverization. A higher aggregate content has an adverse effect on the dynamic tensile strength of concrete. Moreover, the results also suggest that the mechanical properties of the ITZ play a significant role on the dynamic tensile behaviour of concrete.

A new constitutive model of micro-particle reinforced metal matrix composites with damage effects

It is well known that the mechanical behavior of micro-particle-reinforced metal matrix composites (MPMMCs) in service is significantly influenced by the particle size, matrix damage and interface debonding. In order to characterize the mechanical property of such a two-phased elasto-plastic material with the three kinds of effects, a new theoretical model is developed based on the secant modulus method, a low-order strain gradient theory with damage and an effective reduced moduli approach, in which both the size effect of reinforcing particles and the effects of matrix damage and interface debonding are included. As a result, a non-linear elasto-plastic constitutive relation is achieved, with which the stress-strain response of MPMMCs in both uniaxial tension and uniaxial compression tests can be reproduced very well, in contrast to the predictions by the existing strain gradient theories without considering damage. An interesting phenomenon is further found that the dominant role of damage in MPMMCs changes from the interface debonding to the matrix damage with the increase of load in tension test, while the matrix damage always dominates in compression test. The present study provides not only a more comprehensive understanding of the in-service performance of MPMMCs but also a useful theoretical tool for mechanical prediction and optimizing design of other advanced composite materials.