Some experimental observations on crack closure and crack‐tip plasticity

This study presents a methodology for evaluating crack closure and the effect of crack‐tip plasticity on stress intensity. Full‐field displacement maps obtained by digital image correlation are used to obtain the mixed‐mode, crack‐driving force. The methodology allows the quantification of the effect of a range of contact phenomena: effects arising from interlocking, plastic deformation of crack face asperities and wedging generated as a consequence of sliding displacements of fatigue cracks have been identified. By evaluating the effective crack‐tip stress intensity factor, crack opening levels can be quantified for both mode I and mode II. Moreover, the approach can take into account plasticity effects local to the crack in determining the stress intensity factor. All the information can be extracted in a non‐contacting fashion with equipment that can be easily incorporated into industrial environments.