A crystal plasticity based direct method and its application in predicting the shakedown limit of an additively manufactured AlSi10Mg material

In the framework of Design for Additive Manufacturing (DfAM), it is crucial to establish a connection between microstructures including polycrystals and defects, and the fatigue performance of polycrystalline alloy materials. Although Dang Van has already figured out the relationship between multiscale shakedown and the fatigue strength of the material, and several multiscale direct methods (DM) have been developed and applied to various materials, so far existing DMs mainly focus on von Mises or Drucker-Prager materials and cannot reflect the microstructures of the polycrystals. To this end, in the present paper we developed a crystal plasticity based direct method called CP-DM. The method integrates the lower bound theorem with a rate-independent crystal plasticity constitutive model and it is applied to an exemplary polycrystalline material AlSi10Mg made by laser melting deposition (LMD). After the validity of the method is confirmed by incremental analyses, it is employed to predict the shakedown limits of the material and investigate the influence of pore defects introduced during the manufacturing process using many statistically equivalent representative volume element (SERVE) models. The effectiveness of CP-DM is also examined when considering the kinematic hardening of the LMDed AlSi10Mg material, and the impact of the hardening behavior on strength is investigated. The study shows that the established CP-DM method can be a viable means to predict fatigue limit of the polycrystalline materials and especially metallic materials manufactured by additive manufacturing techniques.