Uniaxial Tensile Test Data Research Articles

Characterization of mechanical property of magnesium AZ31 alloy sheets for warm temperature forming

A method based on the numerical inverse approach to characterize the mechanical property of the Magnesium AZ31 alloy sheet for warm temperature forming was discussed in this work. In particular, temperature-dependent hardening and strain rate sensitivity were characterized based on uniaxial tensile test data measured at between 100°C and 300°C with the interval of 50°C. Hardening deterioration associated with micro-void development as well as dynamic recovery and dynamic re-crystallization, observed beyond the uniform deformation limit, was also accounted for. Importance of the proper characterization of the hardening deterioration was confirmed by validating the failure by strain localization in the circular cup drawing test under the warm forming condition. With mechanical behavior properly described, failure with strain localization was predictable without referring to forming limit diagram but directly evaluating strain localization for material elements in this work. Uniaxial compression tests were also performed at various temperatures below 200°C to assess asymmetric behavior in tension and compression.

Embrittlement of structural steel by stress concentrators

The ease of embrittlement characterizes the resistance of a metal to transition from the plastic to the brittle state. The physical significance of the mechanical stability is analyzed in conditions of stress concentration. A method is developed for predicting the ease of embrittlement K msc of structural steel under the action of a stress concentrator on the basis of standard uniaxial tensile test data. The structural quality \(\mu _{P_{ms} }^\sigma \) may be assessed in terms of the residual mechanical stability P ms, which characterizes the remaining resistance to brittleness in conditions of stress concentration. The change in the ease of embrittlement under the action of stress concentrators is analyzed in the case of uniaxial extension and static flexure.

On mixed isotropic-distortional hardening

Mixed isotropic-distortional hardening allows for individual stress–plastic strain relations in different straining directions. Such hardening can be obtained by allowing the parameters in the effective stress function depend on anisotropy functions of the equivalent plastic strain. A methodology to calibrate these anisotropy functions is proposed in this work, and is demonstrated on an austenitic strainless steel. A high exponent eight parameter effective stress function for plane stress states is utilised. The anisotropy functions are calibrated by the use of experimental data from uniaxial tensile test data in three material directions and a balanced biaxial test. The plastic anisotropy is evaluated at a finite number of plastic strains, and it is assumed to vary piecewise linearly with respect to the equivalent plastic strain. At each level of plastic strain, the anisotropy is correctly represented, even if rather large increments in plastic strain are used in the calibration. It was found that there are at least two sets of anisotropy functions which satisfy the conditions in the calibration procedure. The resulting uniaxial stress–strain relations from the two sets of anisotropy functions in four additional straining directions, not included in the calibration set, were compared to the corresponding experimental data. From this validation, one of the anisotropy function sets could be discarded, whereas the other one gave a good prediction of the stress–strain relations in all the four additional directions.

Multiscale modelling of mechanical response in a martensitic steel: A micromechanical and length-scale-dependent framework for precipitate hardening

In this paper, a multiscale finite element (FE) modelling framework is developed with explicit representation of polycrystalline microstructure and sub-micron precipitate structure for a P91 tempered martensitic steel. A dislocation-mechanics-based and length-scale-dependent crystal plasticity model has been formulated to account for slip-based inelastic deformation in the material. The multiscale FE simulations have been validated through the use of uniaxial tensile test data at room temperature. Homogenization analysis is performed to connect the FE models at two length scales. The analysis indicates a strong dependence of dislocation mean free path on the morphology of the sub-micron structure. A linear relationship is found to represent the homogenized constitutive behaviour with respect to precipitate size. Softening effects with respect to precipitate and lath coarsening are identified and quantified at the macroscopic scale through the multiscale modelling framework.

Assessment of creep constitutive properties from three-point bending creep test with miniaturized specimens

Three-point bending creep tests using miniaturized specimen are proposed to assess creep constitutive properties of materials. Based on Norton’s creep law, the analytical model for the three-point bending specimen is given. Through the analytical model, creep parameters can be obtained by regressing the bending test data. Maximum stress approach and reference stress approach are used to convert bending test data to equivalent uniaxial tensile test data. In order to verify these approaches, both three-point bending and uniaxial creep tests of 23CrMoNiWV88 steel are performed. The results show that the derived creep parameters from the bending test data are in reasonable agreement with those obtained from conventional uniaxial creep tests. The equivalent uniaxial creep data converted using reference stress approach are more reasonable than that using maximum stress approach. It has also been found that the large deformation may have a significant influence on the conversion relationship. The results are only accurate at relatively low load levels during testing.

Experimental characterization and computational simulations of the low-velocity impact behaviour of polypropylene

Fil: Torres, Juan Pablo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Mar del Plata. Instituto de Investigacion en Ciencia y Tecnologia de Materiales (i); Argentina; Universidad Nacional de Mar del Plata. Facultad de Ingenieria; Argentina;

Prediction of Matrix Failure in Fibre Reinforced Polymer Composites

Recent development has enabled fibre and matrix failure in a fibre reinforced composite material to be predicted separately. Matrix yield/failure prediction is based on a Von Mises strain and first strain invariant criteria. Alternative matrix failure criteria for enhanced prediction accuracy are discussed in this paper. The proposed failure envelope formed with basic failure criteria intersects with uniaxial compression, pure shear and uniaxial tensile test data points smoothly. For failure of typical neat resin, significant improvement of prediction accuracy compared with measured material data is demonstrated. For a unit cell with a fibre and surrounding matrix with typical material properties, a FEM analysis indicates a significant improvement in prediction accuracy in the pure shear load case and a marginal improvement in the biaxial tensile load case. This paper also provided a preliminary discussion about the issues when material nonlinearity of the matrix material is involved.

On the Work-Hardening of AA 3104-H19 Aluminum Alloy

The aim of this study is to investigate the work-hardening of AA 3104-H19 aluminum alloy. Uniaxial tensile tests were carried out in both the rolling and transverse directions. In the past, some authors have used such uniaxial tensile test data and the Hollomon equation fitted to them to predict the forming limit curves. In a previous study, we showed experimentally that the Hollomon equation exponent, typically 0.07, used in such limit strain predictions is too high and should be approximately 0.04. Other authors have obviously used such a high value because they have compensated for the reduction of limit strains near the plane strain by increasing the Hollomon equation exponent. The reduction of limit strains near the plane strain occurs, as the Marciniak-Kuczynski theory, which the aforementioned authors have used, assumes a local inhomogeneity or a thinner section in the sheet to explain the local necking in stretch forming. In this study, it is shown experimentally that the Hollomon equation exponent in both the rolling and transverse directions is very close to 0.04. It is shown further that the Hollomon or Voce equations do not describe very well the work-hardening of the AA 3104-H19 alloy in either the rolling or transverse direction.

The application of an internal state variable model to the viscoplastic behavior of irradiated ASTM 304L stainless steel

Neutron irradiation of metals results in decreased fracture toughness, decreased ductility, increased yield strength and increased ductile-to-brittle transition temperature. Designers use the most limiting material properties throughout the reactor vessel lifetime to determine acceptable safety margins. To reduce analysis conservatism, a new model is proposed based on an internal state variable approach for the plastic behavior of unirradiated ductile materials to support its use for analyzing irradiated materials. The proposed modeling addresses low temperature irradiation of 304L stainless steel, and predicts uniaxial tensile test data of irradiated experimental specimens. The model was implemented as a user-defined material subroutine (UMAT) in the finite element software ABAQUS. Results are compared between the unirradiated and irradiated specimens subjected to tension tests.

Physically based material model for evolution of stress–strain behavior of heat treatable aluminum alloys during solution heat treatment

A mathematical model based on Kocks–Mecking–Bergstrom model, has been proposed to predict the flow behavior of age hardenable aluminum alloys, under different conditions of solution heat treatment and hot deformation. Considering the published literature, most researchers have taken into account the precipitation and solution strengthening contribution to the flow stress by a constant and some others have ignored these effects. So these available descriptions cannot be applicable directly to different conditions of solution heat treatment. In order to enable these constitutive descriptions to take into account the effects of soaking time and temperature, we introduce in this research a relative volume fraction of precipitation into the flow stress by using the appropriate relationships. The GA-based optimization technique is used to evaluate the material constants within the equations from the uniaxial tensile test data of AA6082 reported by previous researchers.

Nondestructive and Noninvasive Assessment of Mechanical Properties in Heart Valve Tissue Engineering

Despite recent progress, mechanical behavior of tissue-engineered heart valves still needs improvement when native aortic valves are considered as a benchmark. Although it is known that cyclic straining enhances tissue formation, optimal loading protocols have not been defined yet. To obtain a better understanding of the effects of mechanical conditioning on tissue development, mechanical behavior of tissue constructs should be monitored and controlled during culture. However, currently used methods for mechanical characterization (e.g., tensile and indentation tests) are destructive and are only performed at the end-stage of tissue culture. In this study, an inverse experimental-numerical approach was developed that enables a noninvasive and nondestructive assessment of mechanical properties of engineered heart valves. The applied pressure and volumetric deformation of an engineered heart valve were measured during culture, and served as input for the estimation of mechanical properties using a computational model. To validate the method, six heart valves were cultured, and the mechanical properties obtained from the inverse experimental-numerical approach were in good agreement with uniaxial tensile test data. The method provides a real-time, noninvasive and nondestructive functionality and quality check of tissue-engineered heart valves and can be used to monitor and control the evolution of mechanical properties during tissue culture.

Finite element modeling of tube hydroforming of polycrystalline aluminum alloy extrusions

Finite element modeling of tube hydroforming requires information about the anisotropy of the extruded aluminum tube. Unlike sheet metals, the complex geometry of extruded tubes makes it difficult, except in extrusion direction, to directly measure material properties. Therefore, polycrystalline models provide a good alternative for calculating the anisotropy of the tube in all directions and under various loading conditions. Using a rate-independent single crystal yield surface and rigid plasticity, a Taylor-type polycrystalline model was developed and implemented into ABAQUS/Explicit finite element (FE) code using VUMAT. The constitutive model was then used to calculate the crystallographic texture evolution during the hydroforming of an extruded aluminum tube. Initial crystallographic texture measured using orientation imaging microscopy (OIM) and uniaxial tensile test data obtained along the extrusion direction were input to this FEA model. In order to efficiently and practically simulate the tube hydroforming process using the polycrystalline model, sensitivity to the number of grain orientation, total simulation time, and number of finite elements were studied. Predicted results agreed very well with experimentally measured strain obtained from tube hydroforming process.

Modeling of Anisotropic Deformation in Superplastic Sheet Metal Stretching

Currently available models describing superplastic deformation are mostly based on uniaxial tensile test data and assume isotropic behavior, thus leading to limited predictive capabilities of material deformation and failure. In this work we present a multi-axial microstructure-based constitutive model that describes the anisotropic superplastic deformation within the continuum theory of viscoplasticity with internal variables. The model accounts for microstructural evolution and employs a generalized anisotropic dynamic yield function. The anisotropic yield function can describe the evolution of the initial state of anisotropy through the evolution of unit vectors defining the direction of anisotropy during deformation. The generalized model is then reduced to the plane stress condition to simulate sheet metal stretching in superplastic blow forming using pressurized gas. Different ratios of biaxial stretching were investigated, including the case simulating the uniaxial loading condition, where the model successfully captured the uniaxial experimental data. The model is also used to develop a new forming pressure profile that accounts for anisotropy and microstructural evolution.

疑似ひずみ硬化性引張挙動を有する短繊維補強セメント複合材料の設計ガイドライン : その2 飽和複数ひび割れを実現するための実際的な設計クライテリア

High performance short fiber reinforced cementitious composites, named as engineered cementitious composite (ECC), have been realized with reaching several percent of tensile strain capacity. The scope of this study is to establish practical design guidelines for ECC based on micromechanics. These guidelines were set in terms of newly proposed performance indices, stress index and energy index. Uniaxial tensile test data adopting five different ECCs showed these indices successfully express saturation degree of multiple cracking, which enable us to predict the tensile strain capacity of ECCs. As a result, one can design ECC so as to achieve fully saturated multiple cracking and high strain capacity by controlling the performance indices.

Ductility correlations between shear punch and uniaxial tensile test data

The shear punch test was developed to address the need of the fusion reactor structural materials community for small scale mechanical properties tests. It has been demonstrated that effective shear strength data obtained from the shear punch test can be linearly related to uniaxial tensile strength for a wide variety of alloys. The current work explores the existence of a similar relationship between shear punch test data and both the tensile strain hardening exponent and the uniform elongation.

Numerical simulation of acrylonitrile-butadiene-styrene material’s vacuum forming process

Abstract In this paper a vacuum forming simulation together with the experimental results is presented. In order to establish a material model which could describe the polymers deformation behavior precisely, the authors conducted uniaxial tensile tests using the newest type of Meissner rheometer with an acrylonitrile-butadiene-styrene (ABS) material. The tests were conducted for constant strain-rates varying from 0.01 to 1 (1 s−1), at temperatures ranging from 150 to 200°C. A new material model, based on the test data was proposed, in which the combined effects of strain-hardening, strain-rate sensitivity, and temperature variation can be taken into account. Excellent agreement with uniaxial tensile test data was obtained. The vacuum forming processes of a square cup, under different initial temperatures, were simulated employing the proposed material model and the results compared with those of experiment, the simulated final thickness distribution showing a good correspondence to the measured thickness values.

Analytical and experimental study of the die drawing of circular rods through conical dies

AbstractAn analysis is presented of the process of die drawing isotropic polymers, in the form of circular rods, to produce highly oriented materials with enhanced mechanical properties. The stresses in a small element of material undergoing the drawing process have been analyzed using a force‐equilibrium approach and the initial yield and flow stresses in the material have been predicted from the von‐Mises yield criterion. The stress‐strain‐strain rate characteristics of the polymer used in the analysis were deduced from uniaxial tensile test data obtained at the same temperature at which the die drawing occurred. Experimental results are presented of the stress in polypropylene GSE‐108 rods when die drawn at 90°C in a purpose‐built die drawing facility. Novel techniques were used to determine the stress and strain distributions along the die. A comparison of the experimental results and the analytical predictions shows good agreement.

Yield Stress Determination by the Massachusetts Institute of Technology Miniaturized Disk Bend Test

Considerable effort is currently being expended to develop mechanical property tests for various miniature specimens. Bend tests of thin 3-mm-dam disks (standard transmission electron microscopy specimens) have been used by various workers. In this paper a miniaturized disk bend test (MDBT) using a 3-mm-dam x 0.25-mm-thick disk is described and recent progress in extracting uniaxial yield stress values from bend test data is discussed. The method is based on the existence of an initial linear region in the load/deflection curve generated by the bend test. A strong relationship between the load at deviation from linearity and the uniaxial yield stress is found. By simulating observed load/deflection curves using a finite element stress/strain analysis, yield stresses can be calculated from MDBT data. Results using our approach to MDBT for a range of materials are presented, and good agreement with uniaxial tensile test data is shown.

Non-self-similar crack growth in elastic-plastic finite thickness plate

Abstract This work is concerned with non-self-similar crack growth in medium strength metal plates while the loading step, plate thickness and material properties are altered. The three-dimensional elastic-plastic finite element stress analysis is combined with the strain energy density criterion for modeling the material damage process from crack initiation to final global instability including the intervening stage of slow crack growth. Both inelastic deformation and crack growth are accounted for each increment of loading such that the redistribution of stresses and strains are made for each new crack profile. Numerical results are obtained for the center cracked plate configuration under uniform extension with twenty-seven (27) different combinations of specimen thickness, loading step and material type. The fracture toughness S c being related to K 1c for three different materials are predicted analytically from the corresponding uniaxial tensile test data. Effective strain energy density factor S and half crack length a are defined so that the results can be compared with their two-dimensional counterparts. Crack growth resistance curves ( R- curves ) are constructed by plotting S as a function of a . The condition d S / d a = const. is found to prevail during slow crack growth. Translation and/or rotation of the S − a lines can yield results other than those calculated and serve a useful purpose for scaling component size and test time. The minimum thickness requirement for the ASTM valid K 1c test is also discussed in connection with predictions based on the strain energy density criterion. The corresponding K 1c for smaller specimens that exhibit moderate ductility and nonlinearity can also be obtained analytically. In such cases, the influence of loading step can be significant and should not be neglected. Notwithstanding the shortcomings of the theory of plasticity, the qualitative features of non-self-similar crack growth are predicted by the strain energy density criterion. Any refinements on the analytical modeling of the material damage process would only affect the results qualitatively, a subject that is left for future investigation.