Abstract: 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.

Key words: damage parameters, finite element simulation, GTN model, shear strain, small punch test