On the Measurement and Prediction of the Out-of-Plane Displacement Surrounding Cold-Expanded Holes

Abstract

Experimental measurements of the out-of-plane displacement surrounding cold-expanded holes in a 6082-T6 aluminum alloy were made with a 3D optical scanner using the technique of the encoded light-pattern projection in white light. The measured surface profiles have shown the thickness discontinuity along the hole edge due to the effect of the split in the sleeve. An analyticalnumerical solution of the out-of-plane displacement is presented based on existing analytical models. Thus, the results given by the analytical model were then compared with the experimental data and with a finite element (FE) model that simulates the cold-expansion process. The location of the elastic-plastic boundary was estimated as the point at which no change in thickness was observed; a good agreement was found in the comparison of measured, FE and analytical results. The measured surface profiles agreed with those predicted by the FE model and analytical solution. The proposed experimental approach can be used together with FE analysis for predicting the radial and circumferential residual stresses in cold-expanded hole. It is quite versatile and can also be used as quality-control technique in the manufacturing processes of cold-expanded holes.

Effect of Cold Working and Ring Indentation on Fatigue Life of Aluminum Alloy Specimens

“…The residual stress field is asymmetrical around the hole due to extensive shear deformation caused by the split of the sleeve. It varies significantly through the thickness of the plate as a result of the nonuniform deformation produced during the cold expansion, due to different mechanical constraint at different depths . In such cases, it is advisable to place the sleeve with the slit oriented perpendicularly to the crack propagation direction, and the farthest away possible from the edge of the plate.…”

“…The external material will then create a compressive action on the material near the hole, thus forming a residual stress field that extends from the edge of the hole up to a distance equal at least to the hole diameter, as shown in Fig. …”

“…2. 11 The residual stresses created during the cold expansion process, once superimposed to the service stresses, significantly increase the fatigue resistance of the plates with holes, because they reduce the effective stress intensity factor (sum of the stress intensity factor due to applied load, K app , and generated by the residual stress, K res ) and slow down the crack propagation. The maximum compressive residual stress value may reach the compressive ultimate strength.…”

“…while in the plastic region, the Budiansky solution is used: …”

“…where R = 1 is the level of plastic anisotropy of the material; σ s is the yield strength of the material.…”