Ductile fracture prediction for metal sheets using all-strain-based anisotropic eMMC model

In order to predict ductile fracture of metal sheets, the stress invariants based Modified-Mohr-Coulomb (MMC) fracture model was transferred into an all-strain based MMC (eMMC) model under plane stress condition, predicting the fracture strain dependent on strain ratio or Φ angle, instead of stress triaxiality and Lode angle parameter. The strain ratio or Φ angle could be directly measured by digital image correlation (DIC), while the latter required finite element analysis to be determined. This method makes it possible to study material fracture behavior while bypassing plasticity. The eMMC fracture locus can be fully calibrated by fracture strains directly measured from DIC. The fracture strain was also extended by a linear transformation operating to the plastic strain tensor to incorporate the fracture anisotropy. Extensive experimental results of TRIP780 advanced high strength steel and AZ31B-H24 magnesium alloy sheets were used to verify the proposed model. The model was implemented into Abaqus/Explicit as a user material subroutine (VUMAT). Good prediction capability has been demonstrated for these two materials by FE simulation using shell elements.