Finite element implementation of the tension-shear coupled fracture criterion for numerical simulations of brittle-ductile transition in silicon carbide ceramic grinding

Despite great efforts have been made to understand the machining mechanism of brittle materials, few numerical models are available to describe the brittle-ductile transition (BDT) in engineering ceramic grinding due to the fracture mechanism difference in brittle and ductile removal modes. This paper introduces the tension-shear coupled (TSC) fracture criterion for the finite element method (FEM) analysis of the brittle material machining that is capable of describing BDT. With TSC fracture criterion, simulation results of single diamond grain grinding of silicon carbide (SiC) ceramic, including the ground surface/subsurface morphology, grinding forces, and equivalent plastic strain, were compared with those under effective plastic strain (EPS) fracture criterion, the one widely adopted by commercial finite element software. The results show that TSC fracture criterion can better characterize BDT in SiC grinding than EPS criterion, via ground surface/subsurface morphology and tangential grinding force. To experimentally validate the proposed TSC fracture criterion, single diamond grain grinding tests were conducted on SiC with various maximum undeformed chip thickness to demonstrate BDT and compare with the simulation results. The measured ground surface morphology evolution and BDT with the increased undeformed chip thickness matched the results of the FEM simulation with TSC fracture criterion.