PSI - Issue 77

Jiongyi Yan et al. / Procedia Structural Integrity 77 (2026) 135–142 J. Yan/ Structural Integrity Procedia 00 (2026) 000–000

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deformation and fibre displacement (fibre re-orientation) might induce hinge-opening and cracks to propagate through a shorter distance route rather than the long distance from the inner to the outer tip of a corner. Fracture surfaces for different turn angles show distinct features (inset micrographs in Fig. 2a). For the 30° corner, most short fibres are perpendicular to the fracture surface, showing high fibre orientation along the printing and loading direction. There are numerous voids related to fibre pull-out, suggesting limited fibre-matrix adhesion. It can be observed that some resident fibres have voids around the fibre-matrix interface, especially the voids present at the lower surface. This indicates fibre displacement and slipping as the corner was elongated and pulled open, and they may have rotated and were re-oriented to withstand the crack-opening force. The 90° corner showed a large amount of voids, especially at the printed interlayer areas. Fibres were found to be oriented in both directions (upwards and downwards). This may be explained as fibre re-orientation, which resulted in large pores and catastrophic failure throughout the whole surface. Different from smooth surface for the 30° corner, the 150° corner showed a rough fracture surface, meaning the high deformation and toughness as the corner undergoes such large deformation. The fibres were mostly oriented in one direction, potentially due to the fracture occurred near one side of the corner instead of right in the middle. There is also evidence of fibre displacement and re-orientation as numerous voids are present at the fibre-matrix interface, but not as evident as the small-angle corners. This is likely to be caused by the irreversible hinge-opening that occurred at ~40 mm displacement, which transferred the load to the matrix and led to large plastic deformation of the matrix.

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Fig. 2. Static tensile test of 3D printed corners of varied turn angles. The force-displacement curves and inset images of fractured surface and SEM micrographs for 30°, 90°, and 150° corner specimens

3.3. Mechanical simulations To complement the experimental investigation, a two-dimensional finite-element (FE) model of the tensile specimen featuring a 150-degree corner was developed using Abaqus/CAE 2021. This numerical model was developed to gain deeper insight into the failure mechanisms, particularly the stress distribution and progressive damage evolution that are challenging to observe experimentally.