This study investigates the fracture toughness and crack propagation behaviour of short fibre reinforced sheet moulding compounds (SMCs) by performing Compact Tension experiments. Using advanced imaging techniques, including in-situ synchrotron X-ray radiography, visible light, and infrared imaging, a multimodal approach was developed to monitor crack growth and damage evolution in real time. Mechanical performance under load was assessed for carbon, glass and hybrid fibre SMCs, revealing distinct behaviours: carbon-based SMCs exhibited the highest initial load capacity but suffered a rapid loss of strength after damage, while glass-based SMCs maintained strength after crack initiation and showed a more ductile response despite lower stiffness. Hybrid SMCs exhibited a balance of these properties, combining the stiffness of carbon with the ductility of glass to effectively control energy release and limit damage propagation. In-situ synchrotron X-ray imaging reveals complex internal fracture trajectories and energy-dissipation mechanisms that cannot be detected through surface analysis alone. Infrared thermography proves to be more sensitive than visible-light and X-ray imaging, indirectly detecting micro-damage events acting as precursors to failure. The increase of temperature around the crack tip reveals distinct failure signatures — a sharp rise for brittle carbon fibre failure versus a progressive and gradual rise for ductile glass fibre failure. This trade-off between stiffness and ductility was further clarified by an inverse identification using FEM simulations, which showed that carbon fibre laminates exhibit higher fracture toughness than glass despite lower ductility, indicating that strength, rather than ductility alone, governs energy dissipation and crack propagation resistance in these laminates.
Quinoline-based benzoxazine (QBZ) was synthesized and copolymerized with epoxy resin to develop highly thermally stable, multifunctional thermosetting coatings for textile fabrics with enhanced UV shielding, hydrophobicity, tensile performance, and antibacterial activity. The molecular structure of the synthesized QBZ was confirmed by NMR, FTIR, and HRMS, while DSC and TGA were performed to investigate its curing behavior and thermal stability. The QBZ exhibited an exothermic peak with an onset temperature of 205 °C and a maximum temperature of 219 °C, indicating a relatively low polymerization temperature. The resulting Poly(QBZ) exhibited high decomposition temperatures (Td5% and Td10%) of 389 and 449 °C, respectively. Moreover, it exhibited a high char yield of 77% at 800 °C, confirming its excellent thermal stability. For the modification of epoxy-coated textile fabrics, QBZ/epoxy copolymer coatings with weight ratios of 25/75, 50/50, and 75/25 were investigated. Increasing the QBZ content progressively enhanced the UV-shielding and water-repellent properties of the coated fabrics. In particular, Copolymer 3 (75/25 wt%) exhibited the highest water contact angle of approximately 128° and the highest initial UPF values of 74.91 and 76.51 for UV (B, C) and UV(A), respectively, which remained high after 30 washing cycles. In contrast, Copolymer 1 (25/75 wt%) provided the best mechanical and antibacterial behavior, reaching a tensile strength of approximately 52.7 MPa and achieving complete bacterial elimination of S. aureus together with a 3.2-log (99.9%) reduction against E. coli. Overall, the new copolymer system provides a versatile multifunctional coating platform capable of simultaneously imparting UV shielding, hydrophobicity, mechanical reinforcement, and antibacterial functionality to textile fabrics.
Polylactic acid (PLA), a biopolymer derived from bio-based monomers, has attracted considerable attention in fused deposition modeling (FDM) because of its good printability, dimensional stability, and potential for sustainable polymer applications. This study experimentally, theoretically, and numerically investigates the tensile fracture of U-notched and blunt V-notched (BV-notched) diagonally loaded square plate (DLSP) specimens FDM-printed from PLA. To assess the effects of filament architecture and notch geometry, two raster configurations, called cross-ply [0/90]s and quasi-isotropic [0/90/+45/−45]s, and three notch-root radii of 1, 2, and 4 mm are considered. The virtual isotropic material concept (VIMC) is employed to indirectly account for printing-induced anisotropy, while the equivalent material concept (EMC) or modified equivalent material concept (MEMC) is combined with VIMC according to the nonlinear response of each raster configuration. Fracture loads are predicted using the stress-based maximum tangential stress (MTS) and mean stress (MS) criteria, the energy-based averaged strain energy density (ASED) criterion, and the cohesive zone model implemented through the extended finite element method (CZM-XFEM). Incorporating EMC improves the predictions for the cross-ply specimens: VIMC-EMC-ASED provides the best results for the U-notched specimens, with an average absolute discrepancy of 5.6%, whereas VIMC-EMC-MS is the most accurate for the BV-notched specimens, with a discrepancy of 4.5%. For the quasi-isotropic specimens, MEMC produces a more pronounced improvement, and VIMC-MEMC-MS yields the most accurate predictions for both U- and BV-notched specimens, with average absolute discrepancies of 3.6% and 1.7%, respectively. Overall, the proposed simplified framework efficiently predicts the fracture loads of notched FDM-printed PLA components while accounting for printing-induced anisotropy and nonlinear material behavior. Scanning electron microscopy (SEM) is also used to examine the fracture-surface morphology and dominant fracture micro-mechanisms. The observations show that the quasi-isotropic configuration provides slightly greater energy dissipation before final failure than the cross-ply configuration, consistent with the slightly higher fracture loads measured for geometrically similar quasi-isotropic specimens.
