Elastic-plastic Mechanical Properties Research Articles

Experimental behavior and fracture prediction of a novel high-strength and high-toughness steel subjected to tension and shear loading tests

In this study, laboratory testing and numerical simulation methods are used to investigate the mechanical behavior and perform fracture prediction of a novel high-strength and high-toughness steel with a negative Poisson's ratio (NPR) effect under combined tensile-shear loading conditions. A test device capable of meeting different tensile-shear combination test angles is designed and manufactured, wherein the mechanical experiments on the NPR (Negative Poisson's Ratio) steel specimens are carried out at various testing angles. Q235 steel and MG400 steel are used as experimental control groups. The results show that the mechanical deformation of NPR steel is significantly better than that of Q235 steel and MG400 steel. Its tensile-shear test curve has no yield plateau and it has quasi-ideal elastic-plastic mechanical properties. The loading direction gradually changes from tension-dominated to shear-dominated as the tension-shear angle increases, and the strength and deformation of the specimens show a decreasing trend. Based on the laboratory test results, a finite element numerical model of NPR steel is established. A series of numerical simulations are carried out under the conditions of different tension and shear angles and the average stress triaxiality and fracture strain data are obtained. The fracture data of NPR steel are fitted using the Johnson-Cook fracture criterion, and the Johnson-Cook fracture parameters under the tensile-shear test conditions of NPR steel are thus obtained. The numerical simulation verifies that the fracture model can accurately predict the tensile-shear fracture behavior of NPR steel.

Meso-macro constitutive model for frozen salinized sandy soil

In the permafrost areas, the frozen salinized sandy soil is a unique geotechnical component whose mechanical properties will influence the stability of engineering. Thus, formulating a constitutive model for frozen salinized sandy soil has significance scientifically for the design of engineering in cold regions. Combining the theoretical framework of breakage mechanicals for materials, micromechanical analysis method, and homogenization method, a meso-macro constitutive model for frozen salinized sandy soil is put forward in this research. In the proposed model, considering the structure characteristics, the frozen salinized sandy soil is abstracted as a type of inhomogeneous binary materials, the bonded elements composed of the unbroken ice crystals, salt crystals, and soil particles, behaving elastic-brittle mechanical properties, and the frictional elements composed of the broken ice crystals, salt crystals, and soil particles, with elastic-plastic mechanical properties. Due to the disparity in the mechanical characteristics of the constituent materials, the impact of salt concentration on the mechanical parameters of the bonded elements is also taken into consideration. Moreover, the nonuniform distribution of stress and strain with the representative volume element is described by introducing the breakage ratio with the derivation of the strain concentration tensor. The comparison with the tested results demonstrates that the proposed mese-mace constitutive model could simulate the stress-strain and volume law of frozen salinized sandy soil under different confining pressures, which has satisfactory adaptability to reflect the physical and mechanical properties of frozen salinized sandy soil.

Effects of duty cycle on properties of Ni–P–Al2O3 nanocomposite deposited layer prepared by pulse-assisted jet electrochemical deposition

In order to improve the surface quality of the nanocomposite deposited layer, the pulse technology was introduced to the jet electrochemical deposition process, and the Ni–P–Al2O3 nanocomposite deposited layer was successfully prepared. By changing the pulse duty cycle to prepare the composite deposited layer and comparing it with the Ni–P–Al2O3 composite deposited layer prepared under the DC condition and the Ni–P deposition layer prepared under the condition of better pulse duty cycle, the influence of pulse duty cycle on its related performance is explored. In this study, SEM, metallurgical microscope, XRD and EDS were used to analyze the surface morphology, section morphology, phase and composition of Ni–P–Al2O3 deposited layers under different experimental conditions. The hardness and elastic-plastic mechanical properties of the nanocomposite deposited layer were evaluated by hardness tester and nanoindentation tester, and the corrosion resistance of the deposited layer was evaluated by electrochemical workstation. The results showed that the Al content in the deposition layer first increases and then decreases with the increase of the pulse duty cycle, and reaches the highest level of 1.77 wt% when the pulse duty cycle is 60%. The surfaces of the deposited layers prepared under this condition were uniformly dense with better corrosion resistance and the highest hardness value reached was 817.4 HV. At the same time, the elastic recovery ratio he/hmax reached the maximum with a value of 0.36, and the resistance to deformation reached the best.

Elastic-plastic properties of titanium and its alloys modified by fibre laser surface nitriding for orthopaedic implant applications

Laser nitriding is one of the most promising approaches to improve wear resistance of Ti alloy surfaces and may extend the use in orthopaedic implants. In this study, three types of Ti alloys, namely alpha commercially pure Ti (“TiG2”), alpha-beta Ti–6Al–4V (“TiG5”), and beta Ti-35.5Nb-7.3Zr-5.7Ta (“βTi”), were subjected to an open-air laser nitriding treatment. Essential elastic-plastic mechanical properties including elastic modulus, hardness, elastic energy, plasticity index, and hardness-to-elasticity ratio of the laser-treated Ti alloys were characterized using nanoindentation experiment. The results showed that the elastic modulus, hardness and elastic energy values of all Ti samples significantly increased in the nitrided layer compared to respective bare substrates for all three Ti materials. Across different Ti samples, βTi sustained its relatively lower elastic modulus, but presented comparable hardness, elastic energy, plasticity index, as well as hardness-to-elasticity ratio in the nitrided layer compared to the other two Ti alloys. Overall, amongst three medical grade Ti alloys in this study, βTi appeared as the most appealing candidate for joint replacement applications even solely in view of mechanical compatibility when combined with surface laser nitriding. Nevertheless, laser nitriding treatment in this study tended to cause a residual compressive stress on all Ti alloys as displayed by cracks developed in the nitrided layer and analyzed on βTi by X-ray diffraction (XRD) and further nanoindentation tests.

Mechanical Responses of Primary-α Ti Grains in Polycrystalline Samples: Part II—Bayesian Estimation of Crystal-Level Elastic-Plastic Mechanical Properties from Spherical Indentation Measurements

Mechanical Responses of Primary-α Ti Grains in Polycrystalline Samples: Part II—Bayesian Estimation of Crystal-Level Elastic-Plastic Mechanical Properties from Spherical Indentation Measurements

Study on Statistical Damage Theory Model of Tailings in a Metal Ore under the Action of Moisture Absorption and Dehumidification Circulation

In order to explore the variation law of mechanical properties of tailing sand of a metal ore in Hunan Province under the action of moisture absorption and dehumidification circulation, based on the indoor triaxial test results of tailing sand, this paper introduces the statistical damage theory, combined with the physical and mechanical properties of tailing sand, and studies the elastic-plastic mechanical properties of tailing sand on the basis of the Lemaitre strain equivalent theory. Giving full consideration of the change of tailing sand’s pore and volume in the deformation process, an improved statistical damage constitutive model is proposed; it can reflect that the residual strength of tailings after the peak value still has bearing capacity under the action of dry wet circulation. Compared with the results of indoor triaxial consolidation undrained test, this constitutive model is more reliable.

Mechanical Responses of Primary-α Ti Grains in Polycrystalline Samples: Part II - Bayesian Estimation of Crystal-Level Elastic-Plastic Mechanical Properties from Spherical Indentation Measurements

In the second part of the work, a two-step Bayesian framework is utilized for the estimation of values of the single crystal elastic constants as well as the initial slip resistances of the different slip families in the primary α-phase components in the Ti alloys of different compositions. These estimations are based on the spherical indentation measurements presented in part I of this series. The first step of the two-step Bayesian framework established a reduced-order model which captures the dependence of the indentation property as a function of the relevant crystal-level (intrinsic) material properties and the crystallographic lattice orientation in the indentation deformation zone. This reduced-order model is calibrated to high-fidelity results obtained from suitable crystal-plasticity finite element (CPFE) simulations. The second step involved the calibration of the indentation measurements obtained within the primary α-phase (from part I of this series) to the reduced-order model established in the first step. It is demonstrated that the protocols described above result in the successful generation of a comprehensive dataset of single crystal elastic-plastic properties across a collection of Ti alloys while accounting for the implicit uncertainties in the spherical indentation measurements.

Impact of Electrolyte Transference Number on Lithium Dendrite Growth Process

Growth of dendritic protrusions leading to short circuits of cells is presently the largest barrier to widespread usage of lithium metal anodes in commercial lithium ion batteries. Dendrite growth becomes more severe at high current density and low temperature operations because of the onset of diffusion limitations. Improving the elastic-plastic mechanical properties of the electrolyte material can significantly suppress the propagation of dendritic protrusions[1]. However, it has also been argued that enhanced electrolyte transport properties can decrease the propensity for dendrite growth. For example, increased diffusivity of the electrolyte at higher temperature leads to stable deposition of lithium[2], as does increasing the cation transference number of the electrolyte[3]. The propensity for growth of dendritic protrusions can be estimated by solving the mechanical equilibrium, mass transport and charge transport equations, coupled with the nonlinear Butler-Volmer relation. Based on this computational approach, a map correlating growth during operation at 75% of the limiting current density to the electrolyte shear modulus and transference number (see Figure 1) has been developed, showing regimes in which prevention of dendritic protrusion is possible. The results are consistent with experimental observations[4] of dendrite growth in liquid and polymer (PEO) based electrolytes (demarcated by the red regions). This phase-map is expected to help in designing new electrolyte materials that promote dendrite-free lithium deposition.

Study on the Application of Shear Modified GTN Model to Small Punch Test

As an important non-standard test technology, the testing result of small punch test(SPT) is largely influenced by the experiment condition. In the research of SPT, an appropriate mechanical constitutive model of material is much needed. The shear modified GTN model proposed by NAHSHON is implemented into ABAQUS via user defined material subroutine VUMAT to study the material fracture behavior at various stress triaxialities. The undamaged elastic-plastic mechanical properties of the cold rolled silicon steel are obtained by the tensile test. The damage evolution parameters of void nucleation are determined by experiment data of tensile test combined with a large number of simulations. The shear modified parameter that characterizes the contribution of void distortion to damage evolution is identified by the comparison of the results of pure shear test simulations and the experiment data. The shear modified GTN model is used to simulate the small punch test. The results show that, as the void distortion is taken into account in damage evolution, the prediction results of the shear modified GTN model is much more consistent with experiment data than the original GTN model. It comes to the conclusion that the shear modified GTN model can reveal the failure mechanism of material better in intrinsic, and is a better choice to apply in the study of small punch test.

Pseudo-Dynamic Analysis and Construction Methods of Substructure for Division Plate of New Tank

Combined with practical experience a kind of new horizontal storage tank with separate plate was put forward. In view of the lack of experience in the design of the new tank and limitations of carrying out shaking table test for full scale horizontal storage tank, the pseudo-dynamic analysis of separate plate substructure with 5m diameter is done by using ANSYS finite element software combined with the actual engineering. The fluid loads action and mechanical model were simplified, and elastic-plastic mechanical properties of separate plate substructure under the cyclic loading actions were investigated, then deformation and stress distribution of separate plate were obtained. The design thickness for separate plate which in the horizontal storage tank is verified by finite element analysis and the horizontal tank construction methods is given. These can provide technical support to improve the practical design of large horizontal storage tank.

A combined dimensional analysis and optimization approach for determining elastic–plastic properties from indentation tests

Loading–unloading curves obtained from indentation experiments can be used to extract elastic-plastic mechanical properties using the finite element (FE) method. However, extensive computation times are required in such an approach due to the fact that the optimization procedure is based on iterative FE computations. In this study, a combined dimensional analysis and optimization approach is developed for the determination of the elastic-plastic mechanical properties of power law materials, without the need for iterative FE analysis. A parametric study using FE analysis is first conducted to construct the appropriate dimensional functions. The optimization algorithm with either a single indenter or dual indenters is then used to obtain the material properties from the given loading–unloading curves. Different sets of materials properties are used and the accuracy and validity of the predicted mechanical properties using the single indenter or dual indenters are assessed.

Identification of elastic-plastic mechanical properties for bimetallic sheets by hybrid-inverse approach

Analysis, evaluation and interpretation of measured signals become important components in engineering research and practice, especially for material characteristic parameters which can not be obtained directly by experimental measurements. The present paper proposes a hybrid-inverse analysis method for the identification of the nonlinear material parameters of any individual component from the mechanical responses of a global composite. The method couples experimental approach, numerical simulation with inverse search method. The experimental approach is used to provide basic data. Then parameter identification and numerical simulation are utilized to identify elasto-plastic material properties by the experimental data obtained and inverse searching algorithm. A numerical example of a stainless steel clad copper sheet is considered to verify and show the applicability of the proposed hybrid-inverse method. In this example, a set of material parameters in an elasto-plastic constitutive model have been identified by using the obtained experimental data.