Author:

Keywords:

anisotropy, plasticity models, texture, grain shape

Abstract:

The first aim of this PhD study is to validate the predicted plastic anisotropy by using the Taylor, ALAMEL and VPSC models. Therefore the predicted flow stress anisotropy of a low carbon steel and the evolution of the q-value and the deformation texture of three low carbon steel sheets were studied in this thesis. To apply the ALAMEL model to an advanced hardening model, we will encounter a numerical problem, because the ALAMEL sometimes gives oscillated slip rates. The second aim of this PhD study is to revisit the problem of the ALAMEL model. A grain boundary driven (GBD) model was proposed in this thesis to solve this problem. The Taylor, ALAMEL and VPSC models were used to predict the flow stress anisotropy of a low carbon steel sheet (DC06). Then the effect of the texture history on the flow stress prediction was investigated. In the mean time, the qualities of the texture prediction using these three models were checked in order to know whether or not there is a relation between the quality of the texture prediction and the quality of the flow stress prediction. With regard to the flow stress anisotropy prediction for monotonic deformations, neither the isotropic hardening law nor the current models are sufficient yet for the requirement of high accuracy. The effect of the initial grain shape on the q-value and the texture evolution was studied for three low carbon steels (T52, T57 and T61). Both the ALAMEL model and the VPSC model give a similar trend of the grain shape effect on the evolution of the q-value for three low carbon steel sheets. With the input of the initial aspect ratios of the material (the morphological texture), the quality of the texture prediction for rolling is improved. Test results also demonstrate that there is still some gap between the predicted values and the experimental values. The mentioned numerical shortcoming of the ALAMEL model was investigated in detail in this thesis. The effect of the neighboring grain on the slip activities predicted by the ALAMEL model was analyzed. The relaxations introduced by the ALAMEL model on the grain boundaries are classified as parallel, orthogonal and mixed relaxations. The effect of these relaxations on the predicted slip activities was then studied. The grain boundary driven (GBD) model was proposed and tested. The results of the GBD model in comparison with those from the ALAMEL model are given in this thesis.