Influence of the position of fibre misalignment in glass fibre-reinforced polymers on mechanical properties, damage behaviour and traceability via non-destructive tests

Defects in glass fibre-reinforced polymers (GFRP), especially fibre misalignments, are a well-known issue affecting structural performance. This paper investigates how the position of such misalignments influences the mechanical behaviour to deepen the understanding of their influence. GFRP cross-ply laminates with 11 fibre layers were fabricated using the resin transfer moulding process, containing four different types of fibre misalignments. Subsequently, the specimens were evaluated by computed tomography scans and ultrasonic testing and experimentally investigated under tensile, compressive, and bending loading. The obtained mechanical properties were also compared with simulation data. The results of the mechanical tests show that the strength reduction varies greatly depending on the load case, the type of misalignment and its position. Undulations in tensile tests can lead to a strength reduction as low as 8 %, while a single fold located outside the middle layer can reduce the compressive strength by up to 37 %. In service life tests, the effect is even more pronounced. In the worst case, the presence of multiple defects can reduce the service life by up to 94 %. The simulation results showed that a local displacement of individual layers does not represent the extent of undulations and that existing simulation approaches need to be revised and extended. The results of the experiments and simulations demonstrate that both the presence and the position of fibre misalignments significantly affect the material behaviour and are likely underestimated in current research.