# 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
However, the excess material, which consisted of a mixture of adhering \"semi-loose\" particles and partially melted particles, negatively impacted the level of anisotropy. An investigation analyzed the damage characterizations and mechanical behaviors of 3D LPBF-printed re-entrant lattices by comparing the FEA results for a single strut with an ideal geometry and a single strut with the real geometry reconstructed using XCT [93]. A larger stress concentration area at the intersection of the struts was observed for the CT-constructed geometry than the idealized CAD model. Also, the strain localizations were observed to be more obvious. The geometrical irregularities observed for the CT-constructed geometry led to a lower critical buckling load. The ultimate strength and strain at the break of the solid material were reduced by the surface morphology of the CT-constructed geometry when compared with the idealized CAD model. A cost-effective computational method for generating CAD AM representative strut models was developed [94]. Images were collected using X-ray CT (XCT) to generate CAD models of the printed part of the LPBF. The strut models were used to generate a full-lattice FEM model, which was then compared with the idealized CAD model. The results obtained from the CT-constructed model agreed more with the experimental results than the idealized CAD model. An investigation utilized transmitted light images of LPBF-manufactured lattice structures to generate a 2D FEM model with geometrical imperfections [95]. Another study applied an embedded numerical framework to accurately simulate and compare the mechanical behavior of designed and manufactured octet-truss lattice structures [96]. The impact of process defects on the behavior of the final parts was also analyzed. The finite cell method (FCM), which can incorporate the process-induced geometrical defects of the manufactured lattice component into a numerical analysis, was used to directly construct the geometrical mesh from the CT scan data of the printed part. Higher porosities were observed and attributed to the incomplete molten particles remaining intact on the manufactured component surface opposite the build direction. An investigation studied the development of build strategy and lattice unit hole size on the stiffness of an LPBF-printed CoCr microstructure [97]. Comparisons between theoretically circular holes and the actual shape of holes derived from CT measurements were made using FE simulations. The influence of geometrical defects and microstructure characteristics were investigated. A study numerically examined the LPBF-printed defects using CT-constructed geometrical models [98]. The reconstruction of internally formed defects was simplified using voids with equivalent diameters and locations provided via CT scans. External defects included diameter variations, the offset of the cross-section, and undersizing/oversizing. Undersizing and oversizing were shown to alter the overall load-bearing areas directly. The diameter variation and cross-sectional offset induce localization, which can play an important factor in potential failure mechanism(s). An investigation quantitatively studied the respective influences of various types of geometric defects on the Young's modulus, strength, and failure behavior of micro-LPBF fabricated shell lattices [99]. The four investigated geometrical defect types were varying shell thicknesses, holes, levels of surface waviness, and levels of roughness. The XCT-scan data of the manufactured specimens were utilized to generate 3D reconstructed geometries. A numerical model was developed for the SS316L octet-truss lattice specimen, using CT images to generate the simulated CAD model. Defects such as large internal pores and incomplete powder melting were observed [100]. Figure 7: Comparison of von Mises stresses for the whole model, unit cell, and joint node of LPBF-printed structure between idealized CAD model (**left**) and CT reconstructed model (**right**) [93].