Abstract
Laser powder bed fusion (LPBF) is a widely used metal additive manufacturing (AM) method, capable of complex geometry fabrication with high resolution and surface quality. Recent advances have introduced multi-material powder bed AM, which allows for selective powder deposition across multiple layers or within a single layer to truly achieve 3D voxel gradation As this process may combine two dissimilar metals with varying thermal properties along with effects of AM-induced defects, such as as-built cracking, delamination, or residual stresses, are common. Preliminary work has demonstrated that thermomechanical induced cracking at the fusion boundary, leads to premature failure which propagates along the defects at or near the fusion plane. The novelty in this study lies in combining nanoindentation-informed finite element analysis (FEA) to evaluate the use of mechanical interlocking improve mechanical performance in the face of defective interfacial adhesion.
To assess the local mechanical properties across multi-material fusion boundary, nanoindentation is applied to determine the gradient of material hardness. Oliver and Pharr’s analytical method to determine Young’s modulus from nanoindentation is then used to inform FEA. The fusion boundary was modeled as an effective third material partition to generate a digital twin of the fusion boundary. By designing interlocking patterns, we aimed to alternate tensile and compressive stress across the metamaterial structure for an overall reduction in the stress concentration at the site of as-built cracks to reduce the defect’s likelihood of propagating to the state of premature failure. Three mechanically interlocked designs are evaluated to demonstrate the capacity to locally load regions of the fusion boundary in compression despite global tensile loading.
