Beschreibung
The additive manufacturing (AM) industry has proliferated in recent years, the materials used in AM is expanded, and the application of AM products extends from prototype development to end-product manufacture. Among the AM techniques, the laser powder bed fusion (LPBF) attracts the most attention. The LPBF uses a laser to melt metal powder layer-wise to produce free-form products, such as the lattice structure. The lattice structure is known for its high stiffness-to-weight ratio, high strength-to-weight ratio, and outstanding designability. However, we are yet to thoroughly understand the mechanical behavior of the LPBF materials and lattice structures. Being able to predict such products mechanical behavior by considering the LPBF characteristics becomes more crucial than ever. The most remarkable distinct characteristics between the LPBF and conventional materials are the process-induced porosities and material anisotropy. To understand the effects of the LPBF porosities and material anisotropy, we derive the plastic flow rule of the Gurson-Tvergaard-Needleman (GTN) model for the Hill48 yield criterion to form the coupled GTN-Hills model. Then, the proposed model is implemented in ABAQUS with the UMAT subroutine. The effects of porosity and material anisotropy on lattice structures mechanical behaviors under static tensile loading and ultra-low cyclic loading are investigated. In the experimental aspect, the bulk samples are tested under static tensile loading to derive the material behavior; the fractography is performed to identify the failure modes. To compare with the simulation results, we perform both tension and ultra-low cycle fatigue experiments on the lattice structures. In the end, the tensile fracture surfaces of the lattice structure are examined.
