Experimental and numerical analysis of the residual stress distribution in a three-point bending test of a TRIP sheet by using ESPI

In sheet metal forming, residual stresses are related to springback and material failure after the deformation process or during service due to load history. Thus, being able to either calculate or measure such stresses is of great importance. This paper aims to evaluate the use of the Electronic Speckle Pattern Interferometry (ESPI) technique to measure residual stresses on TRIP steel. Residual stresses are measured after springback on specimens used in three-point bending tests; where three bending angles are considered. Experiments are compared with Finite Element calculations in terms of punch force, springback angle and residual stresses. Work-hardening and anisotropy parameters, used in simulations, are experimentally determined by the uniaxial tensile test. Results indicate that advanced hardening models are necessary to increase the accuracy of springback predictions. Nevertheless, residual stress calculations show a good correlation with experimental values. Also, it was proved that ESPI is a powerful technique to measure the residual stress on complex surfaces, as the ones typically encountered in sheet forming processes. Future work includes residual stress predictions for different forming processes.