This study investigates the influence of infill patterns and densities on crack propagation behavior in additive manufactured parts. Through three-point bending tests, force–displacement data were obtained for specimens with different infill patterns, densities, and crack sizes. The results demonstrate that infill density significantly affects the mechanical properties and fracture characteristics of the parts. Higher infill densities result in increased strength but reduced tolerance for deformation, leading to a more abrupt failure mode. The findings highlight the importance of carefully selecting the infill pattern and density to optimize the mechanical performance of 3D-printed parts. Understanding these relationships is crucial for designing robust and reliable structures for various applications in additive manufacturing.

Spall behavior of single and multi-layered hybrid composite structures behind armor was investigated by using shaped charge. Firstly, spall cone angles of Aluminum 5083-H116 and rolled homogeneous armor (RHA) steel as base armor materials were determined without any composite to select base armor. The single and multi-plates composite samples were produced by using S2 glass plain fabric, Kevlar plain fabric and hybrid Carbon-Kevlar twill fabric and epoxy resin system. After that, composite samples were placed behind the selected base armor plates with different distance in between them. The changes of spall cone angle, spall diameter, and penetrated area after shaped charge penetration were determined and analyzed in terms of both material configuration and distance behind the armor plates. As a result, increasing the behind armor distance reduces the jetting area and thus spall distribution decreases. In addition, it can be recommended to use hybrid 1 and 50 mm behind armor distance by evaluating both spall distribution and in-vehicle volume restriction.

This study investigated the effect of fabric parameters on crack propagation in plain‐woven e‐glass reinforced epoxy composite plates. Through numerical analyses, the study contributes to understanding the effect of fabric structure on crack propagation and adopting a more precise approach in the design of composite materials. The yarn fiber volume fraction, shear angle, and yarn spacing parameters were selected as variables for the plain‐woven fabric, and material properties were determined for each parameter using the composite homogenization method. A finite element model was created using the Ansys software package, and stress intensity factors (SIFs) and tear stress values were obtained under mode I loading to investigate the effects of fabric structure on crack propagation. The results showed that as the yarn fiber volume fraction ratio increased, the SIF values decreased and the T‐stress values increased. When evaluated according to the shear angle of the yarn, the lowest SIF value was obtained for the 0‐degree shear angle. The same was observed for T‐stress values as well. Additionally, compared to the fabric structure aligned along the X‐axis, a significant decrease occurred in the SIF value due to the perpendicular fiber density increase to the crack propagation direction with symmetric orientation.

In this study, compression tests were performed on the samples produced with PLA filament with different infill parameters and infill densities by additive manufacturing method and their mechanical performances & static energy absorption capabilities were evaluated. According to the results obtained, it was determined that the samples with triangular and tri-hexagonal infill parameters performed better and it has been shown that time, material and energy can be saved without losing materials mechanical performance.

Semi-crystalline thermoplastics such as polyether ether ketone (PEEK) present a fundamental challenge to conventional fatigue assessment: cumulative plastic energy dissipation increases with fatigue life, contrary to the inverse trend established for metals. This study develops a nonlinear energy-based damage model grounded in continuum damage mechanics, employing strain-controlled cyclic testing data characterised via the Ramberg–Osgood cyclic stress–strain relation and per-cycle hysteretic energy dissipation as the damage-driving parameter. The model incorporates a non-linear energy exponent ( k ) and a damage acceleration term ( 1 − D ) − p to capture the crack incubation-dominated failure mode observed in semi-crystalline polymers. Applied to PEEK, the framework achieves a mean fatigue life prediction error of 4.7%, substantially outperforming the Coffin–Manson approach. Leave-one-out cross-validation across five strain amplitudes yields a stable energy exponent ( k = 3.29 ± 0.05 ) with a maximum prediction error of 15.8%, confirming generalisation beyond the calibration dataset. Independent validation on polyacetal (POM) data from a separate laboratory returns a mean error of 16.9%, demonstrating applicability across semi-crystalline thermoplastics with different chemistries and testing protocols. The consistent damage acceleration exponent ( p = 2.0 ) across both materials points to a shared crack incubation mechanism driven by lamellar-amorphous interface decohesion under cyclic plastic strain. The model operates under isothermal conditions ( f ⩽ 3 Hz, T ⩽ 50 ∘ C) and requires only four to six strain-amplitude calibration points.