Additive Manufacturing with Engineered Defects: An Experimental and FEM Investigation of Fracture Behaviour

Nowadays, metal additive manufacturing (AM) is a well-established technology capable of competing with conventional manufacturing techniques, such as forging or casting. One of the most technologically advanced AM techniques is the Power Bed Fusion—Electron Beam (PBF-EB). This process is gaining industrial reliability thanks to several advantages over conventional techniques, such as high design freedom and material saving. The most relevant advantage for the current study is PBF-EB’s capability to control locally the process parameters and therefore the density of the component. Despite the high control over the density, this method could give rise to undesired micro-structural features such as pores or lack-of-fusion defects. These features act as local stress raisers, leading to fracture nucleation and subsequent propagation, reducing the expected in-service life of components when they are not accounted for. X-ray computed tomography (XCT) offers a solution to investigate the presence of these defects. Indeed, XCT is able to image internal details of objects in three dimensions non-destructively from the meters down to the tens of nanometers length scales, thanks to the penetrating power of X-rays. The XCT study of the tensile damage developing at the internal artificial defects is complemented by the evaluation of fracture surfaces via microscopy. In addition, a study of the fracture behavior is crucial for a deep understanding of the failure mechanisms occurring in-service. In this context, Finite Element Method (FEM). Allowing, through discretization of the body in a set of elements, is used to solve engineering problems with complicated geometries, loadings, and/or material properties, where analytical solutions can not be obtained. This study focuses on the analysis of the damage evolution occurring at controlled internal defects designed for innovative sacrificial components. Printed using PBM-EB, these defects possess special controlled porous layers capable of localizing the final fracture. An interrupted ex-situ tensile test, based on the interchange between XCT and tensile tests, assisted in the characterization of the components by FEM. Four different defect geometries were compared, allowing further gains from this study. It is shown that the FEM can predict the behavior of the sacrificial components with a precision of 10%, regardless of the defect geometry. Moreover, the study of the damage mechanisms reveals that the fracture occurs by the progressive breakage of micrometric molten points within the defect volume, with the largest pores localizing most of the crack propagation. These results will act as a benchmark for subsequent studies, which should further investigate how the defect geometry affects stress localization. The heat distribution analysis during the printing process should also benefit from this study. Overall, this study is considered a step forward to advance the engineering of sacrificial components.