Three-dimensional analysis of the impact fracture of 4340 steel

Abstract

An analysis of the impact fracture of a three-point-bend specimen made of 4340 steel is performed using the finite element method (FEM). In the experiments performed by Sharpe et al. [(1988) WNS/ASD-88-02. The Johns Hopkins University Baltimore, Maryland] the crack tip opening displacement (CTOD) 100 μm behind a prefatigued crack tip was measured. The numerical analyses performed to model this experiment used a three-dimensional mesh which accounted for crack curvature and examined the role played by the residual plastic deformation as a result of the precracking procedure and also the role played by material rate sensitivity of the flow stress. The finite element simulation which included both precracking and strain rate sensitivity effects modeled the CTOD well for the observed 10 μs. From this model, local stress and deformation fields can be assessed. These indicate a significant increase in the impact fracture toughness over the quasi-static toughness. Error estimates and other observations for experimentalists are made, based on different FEM simulations.