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Item type:Publication, Access status: with files , Influence of process parameters on glass fibre-reinforced polymers manufactured through high pressure resin transfer mouldingThe influence of key process parameters on the production quality of glass fibre-reinforced polymers manufactured by high-pressure resin transfer moulding (HP-RTM) was systematically investigated. Uniform ±30° braided preforms were infiltrated under controlled variations of vacuum level, resin discharge rate, and preform fixation. Non-destructive characterisation using air-coupled ultrasonic testing, computed tomography, microscopy but also visual inspection revealed process-induced defects such as in-plane fibre displacements, out-of-plane waviness, voids, and dry spots. Subsequent quasi-static compression testing showed that while Young's modulus remained largely unaffected, compressive strength decreased by up to 26 % under suboptimal processing conditions and was accompanied by a transition from shear-dominated to diffuse, matrix-dominated failure behaviour. Optimal laminate quality was achieved by evacuating the mould cavity to below 1.5 mbar, applying a reduced resin mass flow rate of approximately 10 g/s, and stabilising the preform by dual-sided fixation, resulting in an in-plane fibre orientation of ±30° ± 1.7°. The results establish clear process–structure–property relationships and provide quantitative guidance for robust and reproducible HP-RTM processing.Publicationtype: Journal Article75 23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of the position of fibre misalignment in glass fibre-reinforced polymers on mechanical properties, damage behaviour and traceability via non-destructive tests(Elsevier, 2025-10-01); ; ; ; 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.Publicationtype: Journal Article28 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Manufacture, process simulation, modelling and testing of thick-walled thermoset fibre-polymer composite laminates — a reviewThick-walled thermoset fibre-reinforced polymer (FRP) composites present unique challenges across their manufacturing, simulation, modelling, and testing processes. This paper provides a comprehensive overview of the current challenges and research needs associated with thick-walled FRP, particularly in light of their growing relevance in demanding application domains, such as wind energy. It is important to emphasise that the designation of a laminate as thick-walled is determined not solely by its nominal thickness, but also by the direction of the applied load. In particular, laminates subjected to compressive loading are typically considered thick-walled from a wall thickness of 4 mm or greater. While conventional manufacturing techniques remain applicable to thick-walled FRPs, process adaptations, such as adjusted curing cycles or alternative curing methods, are necessary to mitigate manufacturing defects, e.g. residual stresses induced by inhomogeneous curing due to local temperature overshoot. Modelling of the curing process and accurate prediction of residual stress development remain key areas of ongoing research with significant gaps in understanding. The influence of the wall thickness can also be seen in quasi-static and impact tests. Self-heating must be taken into account in fatigue tests and must be incorporated into future guidelines for the design of thick-walled FRP structures. While well-established non-destructive testing (NDT) techniques are generally applicable, their effectiveness is reduced with increasing laminate thickness due to limitations in resolution. The findings underscore the need for continued interdisciplinary efforts to refine processing and evaluation methods for thick-walled FRP composites.Publicationtype: Review Article72 25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of multiaxial loading and temperature on the fatigue behaviour of 2D braided thick-walled composite structures(Multidisciplinary Digital Publishing Institute (MDPI), 2025-08-31); ; ; ; While size effects in composite structures have been widely studied under quasi-static uniaxial loading, their influence under fatigue conditions, particularly in the presence of multiaxial stress states and elevated temperatures, remains insufficiently understood. This study investigates the fatigue behaviour of thick-walled <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>±</mo><msup><mn>45</mn><mo>∘</mo></msup></mrow></semantics></math></inline-formula> braided glass fibre-reinforced polyurethane composite box structures under varying temperature and loading conditions. A combined experimental approach is adopted, coupling quasi-static and fatigue tests on large-scale structures with reference data from standardised coupon specimens. The influence of temperature (23–80 °C) and multiaxial shear–compression loading is systematically evaluated. The results demonstrate a significant temperature-dependent decrease in compressive strength and fatigue life, with a linear degradation trend that aligns closely between the box structure and coupon data. Under moderate multiaxial conditions, the fatigue life of box structures is not significantly impaired compared to uniaxial test coupon specimens. Complementary non-destructive testing using air-coupled ultrasound confirms these trends, demonstrating that guided-wave phase-velocity measurements capture the evolution of anisotropic damage and are therefore suitable for in situ structural health monitoring applications. Furthermore, these findings highlight that (i) the temperature-dependent fatigue behaviour of thick-walled composites can be predicted using small-scale coupon data and (ii) small shear components have a limited impact on fatigue life within the studied loading regime.Publicationtype: Journal Article46 38