Energy & crack tip stress interactions in mixed mode I/III fracture of DX51 steel sheets

DX51D sheet is subjected to mixed mode I/III loading in a purposely designed fixture apparatus. The resulting stable crack-tip growth, direction, slant angle and typical factory-roof crack were observed and discussed as the loading mixity was varied. The total essential work of fracture or fracture toughness, for each mixity loading, was evaluated adopting energy methods during experimentation, whilst theory details how the total may be separated into its individual mode components. The fracture type and direction of crack path were based on the von Mises failure theory and the fracture criteria of maximum shear stress, maximum hoop stress and maximum normal stress along with the application of Hill’s theory. The findings described clearly establish the link between the applications of the energy based equations governing crack initiation and propagation and the equations describing the stress field surrounding the crack tip in the mixed mode I/III field.