CRACK-PROPAGATION IN THE PRESENCE OF SHOT-PEENING RESIDUAL-STRESSES

This investigation examines the respective effects of peening and re-peening upon the fatigue fracture behaviour of metallic components in the presence of shot-peening residual stresses. Specifically, the work is devoted to highlighting the beneficial effects of compressive surface residual stresses, their relaxation and the associated crack initiation and propagation behaviours of two contrasting materials. Accordingly, room temperature rotating bending fatigue tests were conducted on cylindrical specimens made in aluminium zinc alloy and medium carbon steel. These specimens were first peened and then partially fatigued to a "known" proportion of their anticipated fatigue life. A number of these specimens were then repeened and tested to ultimate fracture; the remainder were used for supplementary tests. The above tests revealed a substantial fatigue life improvement for both the steel and aluminium specimens. However, when re-peened, after being partially fatigued, only the steel specimens showed further life enhancement. Residual stress measurements using X-ray diffraction techniques and fractography using scanning electron microscopy and optical methods were employed, at different stages of the work, to elucidate this discrepancy. © 1990.