Evaluation of numerical prediction tools for anisotropic elasticity and plasticity in additvely manufactured superalloys

Abstract

During recent years, there has been an increasing interest in additively manufactured superalloys for load carrying structures. However, to fully utilize these components, it is necessary to understand how the material response depends on the microstructure. For this purpose, multiscale modelling is often used with crystal plasticity and FEM (CPFEM) for metals. While this method gives accurate results, it is computationally demanding. However, recent research at Chalmers has resulted in a new method, J-AMEN, which does not require FEM analysis and is less time consuming.This thesis aims to compare CPFEM and J-AMEN, in order to investigate if J-AMEN gives as accurate results as CPFEM, while requiring significantly less computational time. This will be done for isotropic grain structure with equiaxed grains and an anisotropic grain structure, elongated grains, which are represented by Representative Volume Elements (RVE’s). Two alloys will be investigated: Alloy 718 and Alloy720Li. The response during loading will be studied using virtual testing of the RVE’s to compute both the homogenized stress-strain response as well as the individual grains’ stressstrain behavior. Both elasticity and plasticity will be studied. Additionally, in the plastic analysis, the texture development of the grains will be studied. For the elastic analyses, there is no significant difference in computational time when comparing the two different methods. Therefore, either of the homogenization methods could be used for multiscale modeling in elasticity and still produce accurate results. However, in the plastic analysis it can take up to several hours to do the CPFEM analysis, while J-AMEN gives results almost instantly. When comparing the homogenized stress-strain behavior for plasticity, J-AMEN gives an almost identical material response to that from CPFEM. Therefore, J-AMEN can be replaced with CPFEM for this type of analysis. The texture analyses for the different grain morphologies and the plasticity analysis for elongated grains was only conducted for CPFEM, as it was not possible to further expand J-AMEN during the time frame of this thesis. By developing J-AMEN in the future, these additional analyses could be included, and the results can then be compared with the CPFEM results in this report.