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|저자명||Namsu Park, Hoon Huh|
|Name||Plasticity 2016 conference|
|Place||Big Island, Hawaii|
This paper is concerned with modeling of fracture-based forming limit criteria for anisotropic materials in sheet metal forming for prediction of the sudden fracture in complicated forming processes. The Lou−Huh ductile fracture criterion is modified using the Hill’s 48 anisotropic plastic potential instead of the von Mises isotropic plastic potential to take account of the influence of anisotropy on the equivalent plastic strain at the onset of fracture. 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 to demonstrate the anisotropy effect on the equivalent plastic strain at the onset of fracture. For the derivation of a modified Lou−Huh ductile fracture criterion, principal stresses are expressed in terms of the stress triaxiality, the Lode parameter, and the equivalent stress 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. This paper also discusses 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 noted that a polar effective plastic strain-based (PEPS) fracture forming limit diagram (FFLD) is suitable for prediction of the sudden fracture of AHSS sheets in complicated sheet metal forming processes on the basis of its path independence and simplicity of measuring strains in real forming processes.