Measurement of Highly Non-Uniform Residual Stress Fields with Reduced Plastic Error

Experimental validations of a recently proposed method for residual stress measurement are presented. The method, specifically designed for highly non-uniform in-plane residual stress fields is applied in this work to measure the residual stresses resulting from four-point bend of an Aluminium 7075-T6 bar. The benefit of the method is that it can reconstruct stress fields without any assumptions of in-plane uniformity. The method uses two cuts, propagated from both side surfaces and collection of full-field relaxation displacement fields from side surfaces using 2D high-resolution digital image correlation (DIC). The reconstructed residual stress agrees well with that predicted by FE modelling and neutron diffraction measurement. In addition, it is shown that induced plastic strain during the relaxation process, which reduces accuracy of the method, is strongly influenced by the direction of the propagation of the cut. This implies that it is possible to reduce substantially plastic strain during cutting if the orientation and propagation of the cut is carefully chosen.