Application of self-consistent crystal plasticity framework as a constitutive description for commercial steel sheets

Abstract

Present thesis investigates potentials of crystal plasticity framework as a constitutive description for commercial steel sheet products. An extensive literature review is presented to introduce historical development of crystal plasticity frameworks. Particularly, the self-consistent scheme is more explicitly discussed as it is mainly investigated in the current work.In Introduction chapter, the constitutive modeling approach based on continuum-scale is given. In addition, some contemporary issues related with the continuum-scale modeling for sheet metal forming are listed. The validity of the crystal plasticity framework is then discussed, as an alternative approach to the continuum-scale modeling. The details of selected crystal plasticity models are presented to help readers who are not familiar with the crystal plasticity framework.In Chapter II an application of a crystal plasticity model for an austenitic stainless steel sample is presented. This application explicitly demonstrates the need of appropriate procedures, which should be performed by the end-user to enhance the accuracy in analysis based on a self-consistent crystal plasticity model. Further, experimental and modeling parameters, which influence the accuracy of model predictions, are demonstrated. Also, an optimal choice for the material parameters is suggested by using a computational optimization tool.In Chapter III, an elasto-viscoplastic crystal plasticity model is used to measure the biaxial flow curve of an IF steel. The biaxial tests were carried out using a hydraulic bulge tester and a Marciniak tooling, respectively. The stress analysis, in the case of Marciniak tooling, was performed based on in-situ X-ray diffraction. The state-of-the-art method for stress analysis based on stress factor and intergranular strain is presented. The crystal plasticity model provided some physical insights for biaxial flow stress analysis, in which development of anisotropy pertaining to crystallographic texture is expected.In Chapter IV, phase transformation induced-plasticity model is incorporated into the elasto-viscoplastic self-consistent crystal plasticity model. Extensive details for the construction of the model are presented. A benchmark study was carried out to demonstrate the influence of various orientation relationships between austenite and martensite. Furthermore, another application is made for a 304 stainless steel sheets based on in-situ neutron diffraction.