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This paper is concerned with the effect of pre-strain on tensile properties of Al5052-H32 under an electropulsing condition. The electroplasticity of Al5052-H32 considering the pre-strain effect is investigated to confirm the formability focused on the level of flow stress and the elongation at fracture. Tensile tests for the pre-strain effect are carried out under two different conditions: pre-straining without the electropulsing and tensile testing continuously with the electropulsing; pre-straining with the electropulsing and tensile testing continuously without the electropulsing. Under the test conditions, electropulsing tensile tests were conducted at the quasi-static of 0.001 s −1 to investigate the effect of the starting point for applying electric current and that of the accumulated electrical energy on the material behavior in terms of the formability. In order to identify the pre-strain effect, the levels of the pre-strain were determined based on the uniform elongation of Al5052-H32 obtained from tensile tests without the electric current. The Digital Image Correlation (DIC) method was used to measure the strain of a specimen. The temperature history of a specimen during the test was measured by using the infra-red thermal imaging camera of FLIR-T621. Experimental results show that the elongation is enhanced as the starting point of applying electric current is delayed for uniform deformation and the elongation increases as the amount of elevated temperature increases with increasing the accumulated electrical energy. [ABSTRACT FROM AUTHOR]

This paper is concerned with modeling of fracture-based forming limit criteria for anisotropic materials in sheet metal forming to predict the sudden fracture in complicated forming processes. The Lou–Huh ductile fracture criterion is modified using the Hill's 48 anisotropic yield function instead of the von Mises isotropic yield function to take account of the influence of anisotropy on the equivalent plastic strain at the onset of fracture. For the derivation of an anisotropic ductile fracture criterion, the principal stresses ( σ 1 , σ 2 , σ 3 ) are expressed in terms of the stress triaxiality, the Lode parameter, and the equivalent stress ( η H , L P , σ ¯ H ) based on the Hill's 48 yield function. Three different kinds of fracture-based forming limit criteria are suggested and investigated with an assumption that the stress state is under the plane stress condition with proportional loading. To determine the parameters of the model proposed, the two-dimensional digital image correlation (2D-DIC) method is utilized to measure the strain histories on the surface of three different types of specimens during deformation and the measurement results are investigated to identify the anisotropy effect on the equivalent plastic strain at the onset of fracture. This paper also discusses about a scaling method for a strain-based fracture forming limit criterion in order to capture the onset of fracture using a single forming limit curve for an anisotropic material. From the comparison of various forming limit criteria suggested, it is concluded that a polar effective plastic strain-based (PEPS) fracture forming limit diagram (FFLD) is suitable for prediction of the sudden fracture in AHSS sheets in complicated sheet metal forming processes on the basis of its path independence and simplicity of measuring strains in real forming processes. [ABSTRACT FROM AUTHOR]

Abstract: A ductile fracture criterion is newly proposed to model fracture behavior of sheet metals for nucleation, growth and shear coalescence of voids during plastic deformation. In the new ductile fracture criterion, void nucleation is described as a function of the equivalent plastic strain, void growth is a function of the stress triaxiality and void coalescence is controlled by the normalized maximal shear stress. The new ductile fracture criterion is applied to construct a fracture forming limit diagram (FFLD) of a dual phase steel sheets of DP780 (1.0t). The FFLD is approximated using both the reverse engineering method and circle grid analysis (CGA) since DP780 fails with slight thickness reduction from the analysis of the fracture surface. Predicted FFLDs are compared to experimental results to validate the performance of the new criterion in the intermediate stress triaxiality between 1/3 and 2/3. The new criterion is also applied to construct the fracture locus of Al 2024-T351 (Bao and Wierzbicki, 2004) to validate the performance of the new criterion in the low and negative stress triaxiality. The fracture locus constructed by the new criterion are close to the experimental data points for all these two materials in a wide stress range from the uniaxial compression to the balanced biaxial tension. The new ductile fracture criterion is recommended to be utilized in finite element analysis to predict the onset of ductile fracture of sheet metals. [Copyright &y& Elsevier]

This paper presents an analysis on magnetic-elasto-plastic buckling and bending of a ferromagnetic rectangular plate with simple supports in applied magnetic fields. A numerical code is built to quantitatively simulate the characteristics of the magnetic-elasto-plastic nonlinear coupling problem by using a finite element method. The numerical results indicate that deformation of a ferromagnetic plate with elastic-plastic deformation is larger than that only with the elastic deformation. The incident angle of the applied magnetic field plays an important role in the deformation of the ferromagnetic rectangle plate: not only affects the magnitude of the deformation; but also the mode of the deformation. The configurations and plastic regions of ferromagnetic rectangular plates for different magnitude of the applied magnetic field are simulated and displayed as well. [ABSTRACT FROM AUTHOR]

This paper proposes a numerical algorithm of a time-discontinuous variational integrator based on the Hamiltonian in order to obtain more accurate results in the analysis of elasto-plastic stress wave. The algorithm proposed adopts both a time-discontinuous variational integrator and space-continuous Hamiltonian so as to capture discontinuities of stress waves. The algorithm also adopts the limited kinetic energy to enhance the stability of the numerical algorithm so as to solve the discontinuities such as elastic unloading and internal reflection in plastic deformation. Finite element analysis of one dimensional elasto-plastic stress waves is carried out in order to demonstrate the accuracy of the algorithm proposed. [ABSTRACT FROM AUTHOR]

This paper deals with the crash energy absorption and the local buckling characteristics of the expansion tube during the tube expanding processes. In order to improve energy absorption capacity of expansion tubes, local buckling characteristics of an expansion tube must be considered. The local buckling load and the absorbed energy during the expanding process were calculated for various types of tubes and punch shapes with finite element analysis. The energy absorption capacity of the expansion tube is influenced by the tube and the punch shape. The material properties of tubes are also important parameter for energy absorption. During the expanding process, local buckling occurs in some cases, which causes significant decreasing the absorbed energy of the expansion tube. Therefore, it is important to predict the local buckling load accurately to improve the energy absorption capacity of the expansion tube. Local buckling takes place relatively easily at the large punch angle and expansion ratio. Local buckling load is also influenced by both the tube radius and the thickness. In prediction of the local buckling load, modified Plantema equation was used for strain hardening and strain rate hardening. The modified Plantema equation shows a good agreement with the numerical result. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces an extended concept of limit analysis to deal with the dynamic equilibrium condition considering the inertia and strain-rate effect for dynamic behavior of structures. The conventional limit analysis method has been applied to only static collapse analysis of structures without consideration of dynamic effects in the structural behavior. A dynamic formulation for the limit analysis has been derived for incremental analysis dealing with time integration, strain and stress evaluation, strain hardening, strain-rate hardening and thermal softening. The time dependent term in the governing equation is integrated with the WBZ-α method. The dynamic material behavior is described by the Johnson–Cook model in order to consider strain-rate hardening and thermal softening as well as strain hardening. Simulations have been carried out for impact analysis of a Taylor bar and an S-rail and their numerical results are compared with elasto-plastic explicit analysis results by LS-DYNA3D. Comparison demonstrates that the dynamic finite element limit analysis can predict the crashworthiness of structural members effectively with less effort and computing time than the commercial code compared. The crashworthiness of a structure with the rate-dependent constitutive model is also compared to that with the quasi-static constitutive relation in order to investigate the dynamic effect on deformation of structures. [Copyright &y& Elsevier]