Analysis of Dynamic Fracture and Crack Arrest of an HSLA Steel in an SE(T) Specimen

A single edge notch tension, SE(T), specimen was used to measure the dynamic fracture toughness and the crack arrest toughness of a tough HSLA steel in the ductile-brittle transition region. The SE(T) specimen was considerably smaller (W = 152 mm) than wide-plate specimens that have been typically used in other crack arrest tests. A thermal gradient was applied across the ligament of the specimen to facilitate a brittle crack initiation in the low temperature region of the specimen. The cleavage crack propagated into warmer and, consequently, tougher material which led to crack arrest. Transient, three-dimensional, finite element analyses of the tests were performed to determine the dynamic fracture and crack arrest toughness of the steel. The analyses employed both linear elastic and visco-plastic constitutive models. Dynamic strain measurements recorded during the run-arrest event were used to determine the crack tip position as a function of time during the event. This information was used as a boundary condition for the analysis. The measured strains were compared with strains predicted by the finite element analysis to validate the model. The dynamic response of the specimen, the effect of crack speed on the driving force, and the evolution of crack tip plasticity during the run-arrest event are discussed.