Experimental characterization and model identification of directional hardening effects in metals for complex strain path changes

The purpose of the current work is the development and application of a new experimental technique and testing device for investigating the complex behavior of sheet metals during non-proportional loading. The method is based on plain strain pure bending, enabling the investigation of large deformation cyclic reversed loading, orthogonal pure bending, as well as springback. The key feature of the pure bending experiment is the absence of contact forces, material slip and friction. Furthermore, during the pure bending test, the strain gradient through the thickness is kinematically prescribed because the specimen is subjected to a plane strain condition in de direction parallel to the rotational axis (Tan et al., 1995), which allows for a straightforward comparison of the pure bending experiments and parallel simulations. The latter is used here via the identification of a recent model for directional hardening effects and arbitrary strain path changes, (Wang et al., 2006, 2008). The current method facilitates experimental investigation of hardening stagnation after reverse loading and cross hardening going well beyond that which is possible with existing methods based on the cyclic shear or tension-shear of sheet metal strips (Bouvier et al., 2005, 2006a,b; Flores et al., 2007.), or pure and three-point bending (Omerspahic et al., 2006; Antonelli et al., 2007; Carbonnière et al., 2009; Yoshida et al., 1998; Weinmann et al., 1988).