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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 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Herausforderungen dickwandiger, duroplastischer Faser-Kunststoff-Verbunde in der Herstellung sowie mechanischen und zerstörungsfreien Prüfung - Ein ReviewDickwandige Faser-Kunststoff-Verbunde bringen eine Reihe an Herausforderungen sowohl bei der Herstellung als auch der Prüfung mit sich. Während sich bei der Herstellung im Wesentlichen die Herausforderung stellt, den Qualitätsverlust so gering wie möglich zu halten, besteht die Schwierigkeit in der mechanischen Charakterisierung darin, den Einfluss weiterer Wechselwirkungsmechanismen, die einen eventuellen Größeneffekt überlagen, zu minimieren. Die betrachtete Literatur zeigt deutlich, dass es nur unter Berücksichtigung aller Einflussfaktoren möglich ist, eine konsistente Aussage über Dickeneffekte und deren zugrundeliegende Mechanismen zu treffen. Neben den Unsicherheiten aus Prüfbedingung und Randeffekten können auch Spannungsgradienten oder Selbsterwärmung einen Einfluss auf die dickenabhängigen mechanischen Eigenschaften von Faser-Kunststoff-Verbunden haben. Entsprechend wurden in der ausgewerteten Literatur z.T. konträre Forschungsergebnisse angetroffen. Eine Reihe verschiedener zerstörungsfreier Prüfmethoden eignen sich sowohl zur Strukturaufklärung als auch zur Bestimmung mechanischer Eigenschaften. Es zeigt sich, dass insbesondere die Ultraschall- und Röntgenprüfungen in der Lage sind, Schädigungen in großen Laminattiefen mit guter Auflösung zu detektieren. Schließlich wird deutlich, dass trotz erheblicher Fortschritte in den letzten 30 Jahren die Beschreibung dieser Thematik nicht abgeschlossen ist, insbesondere hinsichtlich der Modell- und Methodenentwicklung.Publicationtype: Review Article105 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Evaluation and modeling of the fatigue damage behavior of polymer composites at reversed cyclic loading(Multidisciplinary Digital Publishing Institute (MDPI), 2019-05-28); ; ; ; Understanding the composite damage formation process and its impact on mechanical properties is a key step towards further improvement of material and higher use. For its accelerated application, furthermore, practice-related modeling strategies are to be established. In this collaborative study, the damage behavior of carbon fiber-reinforced composites under cyclic loading with load reversals is analyzed experimentally and numerically. The differences of crack density evolution during constant amplitude and tension-compression block-loading is characterized with the help of fatigue tests on cross-ply laminates. For clarifying the evolving stress-strain behavior of the matrix during static and fatigue long-term loading, creep, and fatigue experiments with subsequent fracture tests on neat resin samples are applied. The local stress redistribution in the composite material is later evaluated numerically using composite representative volume element (RVE) and matrix models under consideration of viscoelasticity. The experimental and numerical work reveals the strong influence of residual stresses and the range of cyclic tension stresses to the damage behavior. On the microscopic level, stress redistribution dependent on the mean stress takes place and a tendency of the matrix towards embrittlement was found. Therefore, it is mandatory to consider stress amplitude and means stress as inseparable load characteristic for fatigue assessment, which additionally is influenced by production-related and time-dependent residual stresses. The phenomenological findings are incorporated to a numerical simulation framework on the layer level to provide an improved engineering tool for designing composite structures.Publicationtype: Journal ArticleScopus© Citations 18 354 404 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Damage mechanisms of tailored few-layer graphene modified CFRP cross-ply laminatesA tailored nanoparticle modification approach for fibre reinforced polymers (FRP) is presented that allows exact analysis of the impact of a nanoparticle matrix modification in either 0°- or 90°-layers of cross-ply laminates on the mechanical properties and damage mechanisms. A modification of the 0°-layers unexpectedly increases the quasi-static tensile strength, although dominated by fibre properties. Positive crack stopping effects as well as negative effects, such as accelerated delamination growth, are discussed. The applicability of nanoparticle modified resin systems to improve the performance of FRP-laminates is sensitive to the loading case. For laminates only loaded in tension a modification appears to be advantageous, whereas in case of bending or compression loads the effect of nanoparticles is ambiguous and should be applied carefully.Publicationtype: Journal Article180 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Hierarchical carbon fibre reinforced plastics with tailored nanoparticle modification - Benefits and limitations(Curran Associates, Inc., 2018-06); ; ; ; A tailored nanoparticle modification approach for fibre reinforced polymers (FRP) is presented that allows exact analysis of the impact of a nanoparticle matrix modification in either 0°- or 90°-layers of cross-ply laminates on the mechanical properties and damage mechanisms. A modification of the 0°-layers unexpectedly increases the quasi-static tensile strength, although dominated by fibre properties. Positive crack stopping effects as well as negative effects, such as accelerated delamination growth, are discussed. The applicability of nanoparticle modified resin systems to improve the performance of FRP-laminates is sensitive to the loading case. For laminates only loaded in tension a modification appears to be advantageous, whereas in case of bending or compression loads the effect of nanoparticles is ambiguous and should be applied carefully.Publicationtype: Conference Paper75 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Combined experimental-numerical approach for the 3D vibration analysis of rotating composite compressor blades: An introduction(Curran Associates, Inc., 2018-06); ; ; ; As compressor blades are subjected to highly dynamic loads, there is a particular interest in determining their modal properties under operating condition. Furthermore, intensive research is conducted for the development of fibre-reinforced epoxy blades due to the high specific stiffness and strength as well as the high damping of composite materials. Traditional modal analysis techniques are state of the art to determine the vibration behaviour of non-rotating/stationary blades, where some new approaches show the vibration analysis of rotating blades. These approaches for rotating structures have the disadvantage, that either the excitation or the measurement method are influencing the dynamic behaviour of the investigated structure or the method itself cannot be applied for composite materials. Other techniques do not allow a continuous or full-field measurement of the rotating structure. To determine the vibration behaviour of rotating composite compressor blades, a combined experimental-numerical approach is introduced. Therefore, an experimental system for the vibration excitation and a 3-dimensional determination of the vibration behaviour of rotating components are presented. An overview of the main addressed research topics is given.Publicationtype: Conference Paper52 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of voids and impact damage on the fatigue behaviour of large scale composites(2016-11-01); ; ; ; Defects in laminated composite structures like voids and impact damages have a major influence on the fatigue behaviour. These defects may occur in the manufacturing process and during lifetime of composite parts and lead to matrix cracks within single layers and to delaminations between adjacent layers with different fibre orientations. We investigated the relationship between voids and impact damage and fatigue lifetime. Specimens made of a glass fibre non-crimp fabric were produced by vacuum assisted resin infusion. Voids were introduced by air-bypass simulating a leakage during the vacuum assisted resin infusion-process. Impact damage was induced using a canon. Stringer-panels with the basic dimensions of 1000 mm × 1200 mm and a radius of 1980 mm were tested under multiaxial load situations in a hexapod test rig and a tension/compression-shear test rig.Publicationtype: Journal Article73