PSI - Issue 68

F.J. Gómez et al. / Procedia Structural Integrity 68 (2025) 734–740 F.J. Gómez, T. Gómez-del-Rio, J. Rodríguez / Structural Integrity Procedia 00 (2025) 000–000

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Selective Laser Sintering (SLS), which transformed their cylindrical geometry into a prismatic shape with a rectangular cross-section. The dimensions of the prismatic region were 40 mm x 7.5 mm x 3 mm. The specimens were fixed to the experimental device by threads. Four different U-notches were introduced at the center of the specimen by SLS with nominally tip radii: 0.2, 0.5, 0.8 as 1.0 mm.

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Fig. 1. Sample geometry and critical notch stress intensity factors in polyamide12.

Tests were conducted on two different printing orientations to evaluate their effects on the mechanical properties of the specimens. The first batch of specimens was printed with the deposition direction parallel to the direction of the tensile force, while the second batch was printed with the orientation perpendicular to the axis of the force applied during testing. These two different orientation samples were named 0 and 90, respectively. Approximately 15 specimens of each radius and orientation were tested to obtain a statistically significant amount of data. The maximum load values were measured in all tests, and permit to calculate the critical notch stress intensity factors using the next expression (Creager and Paris 1967): $% = !"# √' ) ( (1) Where R is the notch tip radius and σ TIP is the stress at the tip of the notch under maximum load. σ TIP were obtained by linear elastic plane stress finite element simulations (Crespo et al 2019). 3. Failure criteria In U-notched solids, the stress field near the notch tip can be estimated using the Creager and Paris formula (1967). The approximated stress field depends on the notch radius and the notch stress intensity factor, K U , with the failure criterion being that this factor reaches a critical value, K UC . $ = $% ( , ) (2) Gómez and Elices (2006a, 2006b) examined the validity of expression (2) across an array of linear-elastic materials, including ceramics and PMMA at -60ºC. Their investigation revealed that by introducing a non dimensional formulation based on the fracture toughness and the characteristic length of the cohesive zone model, leads to a function with a weak dependence on material properties. Furthermore, the authors demonstrated that various failure criteria, such as maximum stress, mean stress, the mean strain energy density, the finite fracture mechanics, and the cohesive zone model, yield similar outcomes when their respective parameters were computed using the limits of U-notches. Additionally, all these criteria were restructured into concise expressions, facilitating their application to predict fracture loads. These expressions are collected subsequently: