Identification of the Stress Fields from the Strain Fields in the Isotropic Materials

The identification of the material properties in sheet metals is usually achieved using uniaxial tests. The main attention of this article is focused on the identification of the plastic behaviour of sheet metals using full field measurement. The results were compared for notched specimen and specimen with a hole. These geometries create a heterogeneous strain fields which were measured during the test using high-speed cameras JAI Pulnix TM – 4000 CL which are used in digital image correlation system. DIC is non-conventional optical method for contactless measurement of spatial deformation and displacement and is more and more applied in experimental mechanics. The benefit of using a heterogeneous strain field in the identification process is that a complex state of stress-strain can be analyzed at the same time and much more information can be obtained in a single test. However, the stress field cannot be directly computed from the test and a suitable identification process has to be developed. The article contains virtual fields method (VFM) adapted for strains and plasticity which has been used to identify the hardening behaviour. The results obtained with the VFM have been compared with the results coming from a standard identification made with uniaxial tensile tests.