Identifying the residual stress field developed by hole cold expansion using finite element analysis

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Abstract
The split sleeve cold expansion process is a cost effective method of enhancing the fatigue performance of aircraft fastener holes. However, the 3‐D nature of the induced residual stress fields is not fully understood. For this research, 2‐D and 3‐D models with uniform hole expansion and 3‐D models with expansion produced by contact with a rigid mandrel were developed. The models’ relative capabilities of capturing the residual stress fields were then evaluated. The residual stress profiles varied significantly through the thickness of the workpiece and were also strongly influenced by the direction of mandrel motion. Therefore the uniform expansion models were inadequate. The 3‐D contact models indicate that the mandrel entry face is the critical fatigue location, reporting the lowest circumferential compressive stresses adjacent to the hole. The effect of varying the frictional coefficient and plastic hardening laws were also investigated using the 3‐D contact models.

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