PSI - Issue 68

Bahman Paygozar et al. / Procedia Structural Integrity 68 (2025) 1166–1172 Bahman Paygozar et al. / Structural Integrity Procedia 00 (2025) 000–000

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1. Introduction Additive manufacturing (AM) is increasingly being utilized in various industries, taking account of its merits, such as accelerated time-to-market, lower energy and environmental costs, reduced raw material wastage, and fabricating lattices of high complexity. Utilizing the last benefit of AM, lattice structures of high complexity can be fabricated. Several studies have been performed regarding polymeric lattice materials fabricated by one of the AM techniques (e.g., FFF). For instance, Geng et al. (2019) investigated the fracture behavior of rhombic dodecahedrons (DO) and two kinds of BCC lattice structures under quasi-static tensile loading. Another study was done by Gu et al. (2019) to study the brittle fracture response of the octet-truss lattice structure. They claimed that the Mode I fracture toughness ( !" ) is almost isotropic, whereas the modulus and strength depend highly on the model size and lattice orientation. They used linear elastic fracture mechanics (LEFM) for several specimen types, including single-edge notch tension (SENT), compact tension (CT), and single-edge notch bending (SENB). It was observed that the LEFM can be sufficiently utilized in the structures, including cracks of the linear crack front. The voxel-based finite element model was approved to successfully predict the mechanical behavior of materials (Chai et al. 2012). In this regard, Wingender and Balzani (2022) presented a voxel-based algorithm to efficiently simulate the ductile crack propagation inside heterogeneous structures (e.g., metallic microstructures). Additionally, the 3D voxel-based approach and deep-learning technique were simultaneously used by Yang et al. (2019) to predict the microscale elastic strain field in a two-phase composite. The XFEM technique facilitates a suitable prediction of materials' fracture response, especially crack propagation (Mubashar et al. 2014). This technique has recently been utilized to investigate the fracture behavior of additively manufactured materials. For example, Akhavan-Safar et al. (2020) simulated the fracture behavior of FFF manufactured ABS through this method. Another study investigated the effects of build orientation on the Mode-I fracture toughness of the additively manufactured PLA material (Paygozar and Gorguluarslan 2024). They conducted numerical analyses using XFEM to extract the fracture resistance and crack propagation in FFF-manufactured PLA. This study investigates the fracture behavior of the BCC single-cell lattices using the simultaneous implementation of the XFEM and a voxel-based approach. The BCC lattice type was chosen considering its fabrication without any need for support use, thereby reducing external defects imposed by the sagging problem. The micro-CT imaging technique was utilized to extract three-dimensional voxel models, including all defects inside the lattice arising from the FFF manufacturing technique. The models were then analyzed numerically to extract the lattices' fracture resistance and crack propagation.

2. Experimental study 2.1. Material properties

All the specimens of this study were additively manufactured by an FFF machine (ZAXE X3) from PLA (Porima3D). The process parameters used in fabricating the specimens are listed in Table 1 (Paygozar and Gorguluarslan 2023a). Each specimen was manufactured with five repetitions to capture the exact test results.

Table 1. Process parameters used when manufacturing the PLA specimens. Print Temp. (°C) Bed Temp. (°C) Print speed (mm/s) Layer thickness (mm)

Line width (mm)

Fan speed 100%

Raster angle

215

60

50

0.2

0.45

± 45°

Young’s modulus of the material was previously obtained using the digital correlation method (Paygozar and Gorguluarslan 2023a) and tensile testing dogbone specimens manufactured as per the standard ASTM D638-Type I. The Modes I, II, and III fracture properties (e.g., fracture toughness) of PLA were extracted through different experiments: The Mode I symmetric four-point (4P) bending (Linul et al. 2020) (Fig.1-a), Mode II asymmetric 4P bending (Linul et al. 2020) (Fig.1-b), and Mode III transverse shear cracked plate (TSCP) (Guillén-Rujano et al. 2021) (Fig.1-c) tests, respectively. All the testing conditions (e.g., loading speed) and dimensions of the single-edged notch