Comparison of contouring techniques applied to sheet metal testing

The aim of this work is the simultaneous use and comparison of two different techniques for measuring the three dimensional deformation of a sheet metal specimen subjected to a tensile load. Such measurements are useful for a correct analysis of the mechanical behavior and plastic damage of materials. The former is a hybrid technique based on the combination of 2D DIC and fringe projection; the latter is the 3D DIC. The first method consists in the use of two camera-LCD projector pairs, one for each side of the specimen, in order to acquire the contour map of the out-of-plane displacement with maximum spatial resolution; simultaneously but with lower resolution, the in-plane displacements are evaluated from 2D DIC. The set-up was then integrated with another camera per side, in order to implement the "classic" 3D DIC. The results of these two techniques have been compared, showing a good agreement in general but, although in literature the 3D DIC has been used for trying to study the plastic damage evolution associated to volume change, its reduced spatial resolution leads to a different evaluation, with possible underestimation, of real thickness reduction especially in the very necked zone. © The Society for Experimental Mechanics, Inc. 2013.