Assessing the reliability of fast Fourier transform-based crystal plasticity simulations of a polycrystalline material near a crack tip

Crystal plasticity simulations enable a physically-based description of the micromechanical fields associated with microstructural attributes in polycrystalline materials. Fast Fourier transforms implementation of crystal plasticity (CP-FFT) in periodic unit cells offers increased computational efficiency compared to traditional finite element methods (CP-FEM). Albeit, questions may arise concerning the accuracy of the CP-FFT approach given its underlying spectral framework, specifically in regards to: potential artifacts due to violating the traction-free conditions at internal free surface within the unit cell, Gibbs phenomenon near regions with sharp changes in local mechanical properties, and representation of free surfaces under the constraints imposed by the requirement of periodicity of the unit cell. This paper presents a custom massively parallelized implementation of CP-FFT. A direct comparison of simulation results for polycrystalline deformation near a crack in a Ti55531 alloy is presented between CP-FEM and CP-FFT. The micromechanical fields and slip system level values are quantified and are similar between the two methods. Up to 10% difference in the stress fields is reported at the crack tip and this value dissipates moving away from the crack tip after 5 voxels (7 mu m). The results point towards the reliable use of CP-FFT simulations to model polycrystalline deformation with caveats based on the treatment of the discussed artifacts. (C) 2019 Elsevier Ltd. All rights reserved.