IMPROVING THE FATIGUE CRACK RESISTANCE OF 2024-T351 ALUMINIUM ALLOY BY SHOT PEENING

摘要

The effect of shot peening on the fatigue resistance of a 2024-T351 aluminium alloy was studied using an in situ four point bending fatigue machine under an optical microscope. This system provided the possibility of continuously monitoring crack propagation during a fatigue test. The tests results showed that the fatigue lives for peened specimens are longer than those for unpeened specimens over a wide range of applied stress. They also showed that the crack growth rate of the failure crack increased steadily in unpeened specimens while in peened specimens there was an initial decrease to a minimum, occurring when the crack length was equal to the peening depth. The potential of extending the life of fatigue damaged components was investigated by shot peening specimens which had been fatigue damaged to different degrees. The results indicated that for short cracks (shorter than the peening depth) shot peening totally heals the prior fatigue damage. However, little benefits are achieved in terms of life extension by shot peening specimens with fatigue cracks longer than the peening depth. A fatigue crack model incorporating shot peening effects was used to derive the conditions for crack arrest and the results were presented in the form of a fatigue damage map (FDM). The FDM predicted accurately the fatigue damage healing ability of shot peening.