Component lifing by shot-peening

This investigation systematically approached the effect of peening and repeening upon the fatigue life of partially fatigue damaged components made of high strength 7075 Al-Zn alloy. Total fatigue life improvements better that 300% over the as machined condition and, >40% over the shot peened life were obtained when partially damaged material was shot peened. Maximum benefits were obtained for conditions where approximate to 60% of the life was used prior to peening. Re-peening of partially damaged specimens was also modestly beneficial. However, the results indicate the strong dependency of benefits on the degree of fatigue damage before re-peening, with a detrimental effect for partial fatigue damage lambda>75%. X-ray diffraction measurements of the residual stresses demonstrated that peening or re-peening following partial fatigue, did not produce residual stresses as intense as those associated with the peening of 'virgin' samples.