Finite Element Modeling of Tensile Instability of Sheet Metals Considering Nonuniform Mechanical Properties

In theoretical analyses, such as numerical simulations of the large plastic deformation of sheet metal forming, the material is usually assumed to be ideally uniform; thus, the actual material response during the process cannot be properly characterized. In this paper, a finite element method (FEM) model considering nonuniform material properties is proposed. In the model, the dispersion degree of mechanical parameters is characterized by the microhardness tested from sheet metal samples, and the discrete material properties conforming to the random distribution functions are automatically assigned to the elements in FEM by Python script. The digital image correlation (DIC) method is used to check the tensile instability deformation of sheet metal in the physical experiments of uniaxial tensile tests. The results show that the nonuniform finite element model can reveal the strain transfer and reproduce the diffuse instability in a wide range of plate samples. The deformation feature, crack and its direction are in good consistency with the experiment, and the predicted critical diffuse instability strain is of high accuracy compared with the DIC results. In addition, the influences of random distributions of mechanical properties and the mesh size effects on the simulation results of tensile instability are addressed.