Fracture parameters calibration and validation for the high strength steel based on the mesoscale failure index

Accurately obtaining the material parameters of the damage model is very important for the ductile fracture simulation of steel structures made of high strength steel (HSS). The combination of micromechanics with the uncoupled phenomenological fracture model can be used to obtain the material parameters of ductile fracture locus only from the uniaxial engineering stress-strain relationship. A micro failure index is generally used to link the material fracture under different multiaxial stress status. It is relatively difficult to describe the irregular micro-void evolution using the microvoid radius, and also difficult to tackle the micro void coalescence of the mesoscale using microvoid volume fraction. The mesoscale critical equivalent plastic strain (MCEPS) is proposed as the failure index at the unit cell level to calibrate the fracture locus of the uncoupled phenomenological model in this paper. The fracture locus of the HSS is calibrated by comparing the FE results with experimental data using the homogenized MCEPS and maximum MCEPS at the microvoid surface, respectively. The identified fracture locus is further validated against five stress status, including butterfly shear specimen, butterfly tension specimen, the tensile specimen with the symmetric round notch, tension specimen with a central hole in the middle, and Sandia fracture challenge specimens in 2014. The comparisons of predictions with the experimental results showed that the proposed MCEPS index can be used to obtain the material parameters of the ductile fracture locus.