Effects of expanded and non-expanded hole on the delay of arresting crack propagation for aluminum alloys

The purpose of this paper is to study the effects of inserting an expanded hole or a non-expanded hole at the tip of a fatigue crack on the subsequent delay of fatigue crack propagation. Single edge pre-cracked specimens of two aluminum alloys were used to perform the crack arresting tests under cyclic stress loading. An obvious increase in the delay of crack propagation is obtained for the specimens with expanded hole. The compressive residual stresses produced by the hole expansion process play an important role in increasing the fatigue resistance of the material. The observation of micro-structure at the fatigue failure section reveals that the hole expansion process modifies the condition and properties of the surface layer of materials and affects, significantly the length of the nucleation stage of the fatigue process.