# Roles of Modeling and Artificial Intelligence in LPBF Metal Print Defect Detection: Critical Review
## 3 Advances in Numerical Modeling Techniques for LPBF Defect Detection
### Numerical Simulation Efforts of LPBF Defects
#### 3.2.1 Mechanical Simulations of Reconstructed CT-Scanned LPBF Defects Using FEM  
The mechanical modeling of actual LPBF-printed part defect behaviors can be achieved through various scanning techniques, including x-ray tomography and transmitted light microscopy. At the optimized resolution metrics, the characteristics of the printed part, such as LOF and roughness defects, are detected and computerized, generating 3D CAD models. These models can then be implemented into numerical analysis software to produce structural and mechanical data about the part without performing irreversible physical analyses. Additionally, comparisons between numerical structural analyses of tomography-generated CAD models and original CAD models can help justify structural behavior. An example of LPBF-printed CT-scanned reconstructed geometries evaluated using the FEM is provided in Figure 7. Table 4 lists mechanical FEM analyses of reconstructed CT-scanned geometrical LPBF defects. A study utilized reconstructed CT-scanned data files to analyze the influence of internal defects during mechanical loading using the FEM [86]. The size and location of the  
Figure 6: Comparison between experimental measurements and analytical predictions of the surface roughness of several LPBF-printed parts [84]. pores relative to the outer surface were analyzed, showing that the closer the pores were to the surface, even when they were smaller, the higher the stress concentration factors due to the surface weakness effect. The compressive behavior of hollow-architecture AlSi10 Mg LPBF-printed structures was investigated [87]. The stitching tomography method captured detailed 3D images illustrating the macroscopic hollow structure and local microporosity in the nodes and struts. The 3D FEM code was created in ABAQUS to compare the homogenous matrix with the average initial porosity everywhere and the new heterogeneous model achieved through high-resolution tomography. Localized microcavity and surface roughness defects were reported to affect the stress distribution during compression tests. A study compared FEA results for as-built and as-manufactured 3D porous Ti6 Al4V biomaterial lattice structure samples [88]. The as-manufactured CAD model was reconstructed from XCT images. The two most relevant observed defects were the irregular geometric profiles of struts and axis shifts from the optimum strut main axis. A similar investigation analyzed the effects of surface defects and the geometrical irregularities of as-manufactured geometries of three LPBF-printed AlSi7 Mg periodic truss structures using CT scan data [89]. High-resolution micro-X-ray computed tomographic images were used to generate a geometrical mesh of the AlSi10 Mg LPBF-printed part to investigate the morphology of geometric defects [90]. The CT-produced and CAD-designed FEA stress-strain curves were compared, indicating that the image-based FEA accurately predicted the stress values. A study compared the mechanical behavior of the CAD-built FEA and the CT scan-produced Ti64 (Ti6 Al4V) geometrical lattice [91]. The mentioned defects observed in the metrological analysis and FEA included variable strut cross-section geometries, strut waviness, irregular protrusions, strut cross-section eccentricity, missing and interrupted struts, and uneven distributions of material in the proximity of the junction. An article investigated three porous LPBF-printed Ti6 Al4V structures using a solid network based on a Schwartz primitive unit cell using ABAQUS [92]. The potential effects of the overhanging material on the compressive load capabilities were analyzed. The relatively sharp edges formed from the overhanging zones were assumed to contribute to an earlier yielding. At the same time, the excess material, stated to be more present in the perpendicular plant, appeared to compensate for the sharp edges created by the overhanging zones.