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

Abstract

a b s t r a c tThe 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(Wang et al., , 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(Bouvier et al., , 2006aFlores et al., 2007.), or pure and three-point bending (

Comparison of two models for anisotropic hardening and yield surface evolution in bcc sheet steels

“…This conclusion was substantiated by later crystal plasticity modeling (e.g., Peeters et al, 2002). Related to this are more recent EBSD investigations on DC06 (Boers et al, 2010;Clausmeyer et al, 2012), which imply that the rolling-induced texture in this steel does not change considerably for strains lower than 35% in simple tension. This may be the case in other ferritic steels (e.g., LH800: Clausmeyer et al, 2012;Noman et al, 2010) as well.…”

“…Since various investigations (e.g., Bacroix and Hu, 1995;Boers et al, 2010) suggest that the influence of grain orientation evolution on hardening in ferritic bcc sheet steels such as DC06 is not significant in the range of deformation relevant to the forming processes considered in this work, W P is neglected here for simplicity. Consequently, the evolution relation (8b) for R E depends only on the continuum spin W, and as such is purely kinematic.…”

Strain-path change induced transients in flow stress, work hardening and r-values in aluminum

“…Strategies for the parameter identification and sensitivity analysis were treated by Haddadi et al (2006). Despite of the model's complexity, it has become very popular (Boers et al, 2010;Bouvier et al, 2005;da Rocha et al, 2009;Flores et al, 2007;Oliveira et al, 2007;Thuillier et al, 2010). A texturebased anisotropic yield surface was incorporated by Hiwatashi et al (1997), Li et al (2003) and Reis et al (2002), while strain-rate and temperature sensitivity was included by Uenishi and Teodosiu (2004).…”

Modeling strain-path changes in aluminum and steel

“…Bauschinger effect (Bauschinger, 1881;Hasegawa et al, 1975) and hardening stagnation (Boers et al, 2010;He et al, 2014) may be observed after reverse SPCs, while orthogonal hardening or softening Hasegawa et al, 1975;Manopulo et al, 2015;Peeters et al, 2000;Tarigopula et al, 2008) may happen after orthogonal SPCs. However, the transients may sometimes influence the subsequent part of the stress-strain…”