Abstract: The effect of cold expansion of holes on the fatigue crack initiation life of LY12CZ aluminium alloy sheets are experimentally investigated, and a quantitative expression of the fatigue crack initiation life is also given. The observation during fatigue testing shows that, after the cold expansion of holes, the fatigue crack almost initiates on the entry face, from which the mandrel is introduced into the holes, Therefore, it may be thought that the entry face is less resistant to fatigue crack initiation. In addition, the assumption on the equivalence of the residual stress and strain hardening conditions on both of the entry and exit faces may be questionable.

Key words: fatigue, crack initiation, cold expansion, aluminium alloy.