Experimental and theoretical assessment of mode II fracture toughness for cracked ductile specimens with high strain-hardening

In this research, the fracture toughness of O-notched diagonally loaded square plate (DLSP) samples with pre-existing cracks is investigated theoretically and experimentally under pure mode II loading. These specimens are made of the stainless steel 316L, which is highly ductile and has great strain-hardening. For theoretical prediction of the fracture toughness of desired specimens, the Fictitious Material Concept (FMC) is employed. By using FMC, complex elastoplastic failure analysis can be avoided and by performing linear elastic analysis, the fracture toughness of DLSP specimens can be estimated. Based on the assumptions of FMC, the stainless steel 316L can be replaced with a virtual brittle material having linear elastic behavior. Then, by coupling FMC with mean stress, generalized mean stress, maximum tangential stress, generalized maximum tangential stress, strain energy density and generalized strain energy density criteria, fracture toughness of the cracked DLSP samples are estimated. To verify the estimated fracture toughness, several fracture tests are performed on DLSP specimens. Experimental observations reveal that these specimens experience significant plastic deformations at the onset of crack propagation. It is shown that combination of FMC with six linear elastic brittle fracture criteria is quite successful in predicting the crack growth instance in ductile DLSP specimens.