Evaluation of damage in materials due to fatigue cycling through static and cyclic small punch testing

Results of an experimental investigation of damage due to prior fatigue of metallic materials through static and cyclic Small Punch Test (SPT) is presented in this paper. Monotonic small punch tests were performed on virgin specimens of copper, brass, and stainless steel (SS-304) as well as on fatigue damaged copper samples to understand the effect of prior damage on tensile properties. It is observed that, the slope of initial linear portion of load-displacement response when normalized by initial thickness of the SPT specimen is proportional to the elastic modulus. Damage fraction estimated based on conventional damage theories was found to correlate reasonably with the data derived from static small punch testing. Fatigue response of materials was evaluated through a novel cyclic small punch testing under global compression-compression loading. Variation of punch displacement and hysteresis energy was monitored as a function of the number of cycles. Distinct change in punch displacement, cumulative hysteresis energy, was observed prior to complete failure of specimen. An empirical equation relating to the level of damage and hysteresis energy during cyclic SPT is proposed.