Introducing texture into anisotropic VBO to model the deformation of Zirconium alloys

Abstract

There is no unified phenomenological model available for Zr alloys that allows for the inclusion of a complete set of texture input parameters in order to describe the anisotropic behaviour during plastic deformation at different strain rates and thermal creep. This research shows how AVBO, an anisotropic version of VBO, can be enhanced by introducing single crystal based tensors to describe the material response to different Kearns factors, which uniquely describe the texture of a sample with two numbers only. It is demonstrated with the aid of published thermal creep test data that small tensile deformation behaviour of Zr-2.5Nb is consistent with predominant slip of Zr alloy crystals parallel to their single crystal α basal planes, supporting the strategy to model the behaviour of these HCP materials with a phenomenological constitutive model. It is demonstrated that the new version of AVBO, ATXVBO, predicts trends consistent with a slip mechanism parallel to the basal planes. Multi-objective optimization was employed successfully to determine the set of 67 constants. It is proven that the theory relies on a limited number of tests to perform optimization of all the unknown constants. Numerous validation and sensitivity evaluations were performed to test the optimized solutions despite the limited availability of plastic deformation test data with documented texture information. It is demonstrated that, in order to capture dynamic strain aging effects, different strategies will be required at different evaluation temperatures. It is also shown that although texture variation can be accommodated that different manufacturing routes each requires a unique optimized set of constants.