Evaluation of residual stress in ultrafine-grained aluminum tubes using shearography

Abstract

Parallel tubular channel angular pressing is a novel severe plastic deformation method for producing ultrafine-grained metallic tubes. The objective of this work is to determine the residual stresses in parallel tubular channel angular pressing processed tubes using an incremental blind hole drilling with digital shearography instead of conventional hole-drilling method of strain gauges. Shearography is a full-field speckle interferometric method employed to measure both in-plane and out-of-plane displacements. The displacement derivative distribution due to hole drilling is calculated by analyzing unwrapped phase maps. Using image processing fringe analysis, the optical data involved in the displacement derivatives are converted into the values of residual stresses. The results have shown that an increase in the number of parallel tubular channel angular pressing pass would lead to a decrease in residual stresses that attributed to the low stress gradients along the thickness and length of the parallel tubular channel angular pressing processed tubes. Comparison of the residual stress values obtained from the shearography method with those from finite element modeling has shown good agreement of the stress values, indicating the suitability of shearography technique for stress evaluations in the parallel tubular channel angular pressing process.