Strain Path Change Effects in a BCC Crystal Plasticity Framework

2006-10-26
The presentation outlines a temperature dependent, strain rate sensitive crystal plasticity model at finite strains which is aimed to be used in the modeling of strain path change effects for BCC structured materials. Plastic anisotropy in BCC crystals originates from different sources at different length scales. Slip asymmetry and intrinsic anisotropic effects caused by screw dislocation cores are the ones at the micro level, the development of dislocation sub-structures is relevant at meso level, and finally the texture development which can be considered at the macro level plays a role. The observed anisotropy during a strain path change is due to a combination of all these effects at different length scales. It is questionable which effect dominates the anisotropy observed during the change of the loading path for BCC metals. Recent works showed that the influence of the dislocation sub-structuring prevails at moderate strains for BCC crystals. During the deformation of a material, plasticity starts with the movement of dislocations and further deformation causes these dislocations to cluster and form regions with a high dislocation density, enveloping regions with a low dislocation density. The structures accordingly obtained are called dislocation cells and a number of cells are surrounded by another structure called cell block boundaries. A change in the loading direction of the material leads to an altered evolution of these structures which results in a plastic anisotropy effect. The global goal of the present work is to arrive at a material model that is capable of describing the mentioned phenomena. The development of an adequate BCC crystal plasticity framework supports this objective. BCC crystals have a number of peculiar features that are not observed in other crystals. Hence a crystal plasticity model based on the intrinsic properties of BCC crystals is the central theme in this work. Recent developments concerning the identification of the macroscopic slip planes are presented and included in the model where the active slip plane family and the nature of the slip depend highly on the temperature. The flow stress of BCC single crystals shows a surprising dependence on the orientation of the crystal, the temperature and the rate of deformation which makes BCC materials different from others. Non-planar spreading of the a/2<111> type screw dislocation cores is another feature that makes them special. The main result of this phenomenon is the violation of Schmid's rule in BCC crystals, resulting in an intrinsic anisotropic effect. All the pronounced aspects are presented in the context of uniaxial stress-strain curves. A good agreement is obtained between the simulations and available experimental data.
Citation Formats
T. Yalçınkaya, “Strain Path Change Effects in a BCC Crystal Plasticity Framework,” presented at the Ninth Engineering Mechanics Symposium (26 - 27 October 2006 ), De Werelt, Lunteren, Netherlands, 2006, Accessed: 00, 2021. [Online]. Available: https://hdl.handle.net/11511/71979.