Design of New Tests for the VFM

Abstract

Over the years, much effort has been dedicated to solving the inverse problem consisting in extracting the materials mechanical constitutive parameters from full-field deformation maps. However, the next very important question is which mechanical test configuration will give the optimal identifiability. Indeed, now that the constraints arising from the necessity to have well-controlled test geometries and loads to have a priori stress distribution information are relaxed, the design space for test configuration becomes nearly infinite and some strategy must be devised to come up with novel relevant tests that will contain the required mechanical information (i.e., activate at best all the parameters to identify). In the early days, such tests were mainly derived from existing configurations (unnotched Iosipescu test) or imposed by the specimen geometry (ring compression test). However, some attempts at test design and optimization have been performed. This section is dedicated to the presentation of this work. First, a very basic approach based on strain balancing is presented to design a T-shaped specimen. Then, with the availability of optimized virtual fields, the η parameters have been used to build up cost functions but this approach proved to be too restrictive. Finally, a recently developed complete identification simulator is detailed, which takes into account all the stages from image forming down to identification. This is the ideal tool to evaluate identification performance and design novel test configurations.