Predicting residual stresses in SLM additive manufacturing using a phase-field thermomechanical modeling framework

Additive manufacturing (AM) of metallic components has recently become a viable option for series production. In this, the powder of various metallic materials such as steel and aluminum can be processed layer-by-layer to produce dense parts with excellent properties. One of the major challenges in this process is the occurrence of residual stresses, which negatively affect the strength and functionality of the produced components. Understanding the mechanism of distribution of these stresses and the detrimental deformations is one of the main themes covered in this work. In the numerical treatment with the finite element method, a phase-field model (PFM) for phase-change materials is utilized together with a thermo-elastoplastic model to simulate the multi-layer AM process and to evaluate the occurring residual stresses. Using the PFM allows tracking the diffusive melting front and, thus, distinguishing between the melted (soft) and the unmelted (hard) states of the material. One of the novel contributions is the definition of a phase-field history variable, which can capture the irreversible process of metallic powder melting. Additionally, phase-field-dependent material properties are proposed. The coupled governing equations are solved in the open-source FE package FEniCS Project, where three-dimensional initial-boundary-value problems are introduced and the results are compared with reference data from the literature.