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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50 cycles, the peak force of the 30 o corner specimen showed ~23% reduction in the peak force, as the secant stiffness at peak (equivalent to the peak force divided by maximum displacement as per cycle) decreased from 159.6 MPa to 123.1 MPa. In addition, hysteresis energy per cycle was calculated based on the loop area between the loading and unloading curves, and this is an indicator viscoelastic conditioning as a measure of the energy dissipated as heat and damage in the material during the cycle. The hysteresis energy per cycle decreased by 52.4% from 145.2 N*mm to 69.2 N*mm. This showed the elastic energy dissipation due to internal friction, molecular rearrangements, and damage mechanisms related to the plastic deformation. During the repeated large deformation, fibre debonding and dislocation (displacement, slipping, and pull-out) may occur, which increases the chance of crack initiation and propagation. Since there is no known treatment to improve the fibre wetting and adhesion with the matrix for this material, the weak fibre-matrix interfacial bonding and adhesion may be attributed to the mechanical degradation in the cyclic tensile. As fibres could not be fully adapted with large deformation in the loading direction, microcracks at the fibre-matrix interfaces may be initiated and propagate. Crack propagation further weakened the matrix as void volume increased. Together with interlayer debonding, these factors contributed to mechanical degradation in the cyclic tensile test. Overall, the cyclic tensile test shows limited fatigue properties of 3D printed corners with large strain. Note that the 30 o corner had relatively high longitudinal alignment and high specific strength compared to other corner angles in static tensile test, it can be inferred that sharp corners would exhibit more significant degradation and fatigue, which is to be explored in the future.

Relative change of peak force

Fig. 4. Cyclic tensile tests with displacement-controlled mode and force-displacement curves of 3D printed 30 o corners with an inset plot for relative change of peak force over cycles. 4. Conclusion We studied 3D printed angular corners in terms of fibre orientation and mechanical properties via both experiment and finite-element analysis. The main-axis fibre alignment was low when the turning was more transverse, while the lateral alignment increased, showing high induction by the flow direction. The out-of-plane alignment increased as the turn angle increased, due to over-extrusion and overlapping which encouraged fibre interlayer diffusion. The