Failure Prediction in Hole Expansion Test Using Plastic Work Criterion

Abstract

Although the uniaxial tensile test gives information about the formability limits of the material, different formability tests are required to obtain the stretch formability limit of the material. Hole expansion test is a process performed to obtain the formability limit considering the stretching conditions of a sheet with a hole. For automotive industry, this forming limit has a crucial role in the reliability of the engineering parts exposed to the several stretching modes. In the present study, the hole expansion tests of twinning induced plasticity (TWIP940) and transformation induced plasticity (TRIP590) steel sheets were simulated using finite element method. Implicit Msc. Marc software in conjunction with the Hypela2 user subroutine file, was used for the numeric solutions. The plastic work-based failure criterion was incorporated into the subroutine and the homogeneous fourth-order polynomial-based yield function (HomPol4), was considered to define the bound of the yield loci. Hole expansion ratio and the failure strain predicted from simulations were compared with the experimental results to assess the capability of the HomPol4 criterion. It was seen that the numerical results were in good agreement with the experimental results for both steel sheets. Moreover, failure stroke values were predicted using the failure criterion. Stroke value was successfully predicted for the TWIP940 steel, which does not exhibit a significant amount of strain localization. On the other hand, a difference between the numerical and experimental results was observed for TRIP590 steel sheet.