TY - THES A1 - Nielow, Dustin T1 - Einfluss fertigungsbedingter Imperfektionen auf die Schwingfestigkeit von FKV-Schalenstrukturen in Sandwichbauweise T2 - BAM-Dissertationsreihe N2 - Rotorblätter von Windenergieanlagen (WEA) weisen häufig nach wenigen Jahren, lange vor dem Erreichen der prognostizierten Lebensdauer von 20 bis 30 Jahren Risse in der Blattschale auf. Die Folge sind aufwendige Reparaturen am installierten und schwer zugänglichen Rotorblatt und der kostenintensive Nutzungsausfall durch den Stillstand der WEA. Als mögliche Initiatoren für die Schäden in der Blattschale der Rotorblätter gelten fertigungsbedingte Imperfektionen. Für die Untersuchung des Einflusses dieser Imperfektionen auf das Ermüdungsverhalten der Rotorblätter wurde an der BAM (Bundesanstalt für Mate-rialforschung und -prüfung) ein Prüfstand für statische und zyklische Versuche von Schalensegmenten im intermediate scale entwickelt und betrieben. Die untersuchten Schalensegmente in Sandwichbauweise sind der Rotorblattschale von WEA im Hinblick auf die Strukturmechanik, die eingesetzten Halbzeuge, den Laminataufbau und dem eingesetzten Fertigungsverfahren ähnlich. Als Imperfektionen wurden verschiedenen Variationen von Lagenstößen in die Hautlagen und Schaumstöße mit Breitenvariation in den Stützkern reproduzierbar eingebracht. Die Überwachung des Schädigungszustandes während der Schwingversuche unter realistischen Lastszenarien erfolgt über eine kombinierte in situ Schädigungsüberwachung mittels passiver Thermografie und Felddehnungsmessung. Mit den durchgeführten Schwingversuchen und der begleitenden Überwachung des Schädigungszustandes ließen sich die Schadensinitiation und die signifikante Herabsetzung der Lebensdauer durch die eingebrachten Imperfektionen zweifelsfrei nachweisen und entsprechende Konstruktionshinweise für die betriebssichere Auslegung von Sandwichstrukturen ableiten. N2 - Wind turbines often exhibit cracks in the blade shells after only a few years in service, significantly before their expected 20 to 30 year design lifespan. This leads to complicated repairs on difficult to reach rotor blades, and can cause a cost-intensive standstill of the turbine. A possible source of these defects in the rotor blade shells are the imperfections which occur during production. In order to investigate the effect of these imperfections on the fatigue behavior of rotor blades, a test rig was developed at the BAM (Bundesanstalt für Materialforschung und -prüfung) upon which intermediate scale static and cyclic-fatigue testing could be performed. The complementary sandwich shell specimens developed and investigated with the test rig are representative of the outer shell of wind turbine rotor blades in terms of materials and manufacturing processes, as well as structural mechanics. The specimens were built with reproducible imperfections, including laminate overlaps in the face sheets and gaps of varying size in the foam core. The damage condition was monitored during cyclic-fatigue testing under realistic load cases using a combination of in-situ passive thermography and strain field measurement. The cyclic testing and parallel non-destructive structural health monitoring of the shell specimens showed the imperfections to significantly influence the damage initiation and decrease the component service life. The results can be used accordingly as recommendations for operationally more reliable design of sandwich structures. T3 - BAM Dissertationsreihe - 170 KW - Erneuerbare Energien KW - Windenergie KW - Verbundwerkstoffe KW - Betriebsfestigkeit KW - Komponentenprüfung KW - Renewable ernergy KW - Wind energy KW - Intermediate scale KW - Composites KW - Fatigue PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-546701 SN - 1613-4249 VL - 170 SP - 1 EP - 178 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-54670 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Trappe, Volker A1 - Kraus, David T1 - Thermo-mechanical fatigue of glass fiber reinforced polymer N2 - Glass fiber reinforced polymer (GFRP) materials in practical applications have to endure cyclic mechanical loading in a wide temperature range (e.g. aircraft applications, automotive, wind turbine blades). In this study the static strength and fatigue behavior of GFRP was investigated in a temperature range from 213 K to 343 K. Therefor the coefficients of thermal expansion of the composite as well as the matrix are measured in this temperature interval. The inverse laminate theory was extended and used to calculate the inter fiber-failure effort for a virtual UD-layer according to the layer wise strength approach. The experimentally determined results are compared with the micro-mechanical model according to Krimmer, which has been enhanced to include the effect of temperature and fiber-perpendicular failure modes. A correlation between matrix effort, the dilatational strain energy of the matrix and the damage state of the specimen is demonstrated. It is shown that a fatigue life assessment can be performed with the aid of a temperature-independent master fatigue curve, as it was similar done for the fatigue behavior of CFRP and GFRP to very high load cycles at room temperature. T2 - ICFC8 - The 8th International Conference on the Fatigue of Composites CY - Online meeting DA - 23.06.2021 KW - Glass fibre reinforced plastics KW - Fatigue KW - Thermo-mechanical-loading PY - 2021 AN - OPUS4-52910 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Kraus, David T1 - Ermüdungsverhalten von Glasfaser-Kunststoff-Verbunden unter thermomechanischer Beanspruchung T2 - BAM-Dissertationsreihe N2 - Die Werkstoffgruppe der Faser-Kunststoff-Verbunde (FKV) hat sich aufgrund ihrer hervorragenden Leichtbaueigenschaften unter anderem im Sportgerätebau, in der Luft- und Raumfahrt und in der Windenergieindustrie etabliert. Die so hergestellten Strukturen sind in der Regel nicht nur mechanischen Belastungen, sondern auch thermischen Lasten in einem breiten Temperaturspektrum ausgesetzt. Dennoch ist die Auswirkung des Temperatureinflusses bei einer Kombination von thermischer und mechanischer Last auf die Lebensdauer von Strukturen aus FKV bisher nur wenig untersucht. Im Rahmen dieser Arbeit wird der Einfluss von Temperaturen zwischen 213 K und 343 K auf einen Glasfaser-Epoxidharz-Verbund experimentell untersucht. Das Material wird in diesem Temperaturbereich eingehend charakterisiert: Es werden sowohl die thermomechanischen Eigenschaften von Faser- und Matrixwerkstoff als auch die des Verbundes ermittelt. In einem weiteren Schritt wird dann der Einfluss der Temperatur auf die Schädigungsentwicklung im quasi-statischen Lastfall sowie unter schwingender Ermüdungsbeanspruchung bei verschiedenen FKV-Mehrschichtverbunden analysiert. Basierend auf den experimentellen Daten wird ein Zusammenhang zwischen der Schädigung und der Anstrengung der Matrix innerhalb der Einzelschicht demonstriert. Die Matrixanstrengung wird mithilfe eines mikromechanischen Modells unter Berücksichtigung der thermomechanischen Eigenspannungen analytisch berechnet. Bei Querzugbeanspruchung kann gezeigt werden, dass eine Vorhersage der Schädigung in Abhängigkeit der Volumenänderungsenergie innerhalb der Matrix getroffen werden kann. Mithilfe des Konzepts der Matrixanstrengung ist eine Vorhersage der Lebensdauer des Werkstoffs unter schwingender Ermüdungsbeanspruchung in Abhängigkeit der Einsatztemperatur möglich. N2 - Due to their superior lightweight properties, fiber reinforced polymer (FRP) materials are well established in various fields, such as sports equipment, aerospace or wind energy structures. These structures are not only subjected to mechanical loads, but also to a broad spectrum of thermal environments. However, the impact of temperature on the fatigue life of thermomechanically loaded FRP structures is barely investigated to-date. In the scope of this work, the influence of temperatures in a range of 213 K to 343 K on a glass fiber reinforced epoxy polymer is experimentally examined. An extensive thermo-mechanical characterization of the static properties of the material is performed. The neat resin and Fiber material are investigated, as well as the composite. In addition, the impact of thermal loads on the damage evolution under quasi-static as well as cyclic fatigue loading is investigated for different multi-angle laminates. Based on the experimental data, a correlation is shown between damage and matrix effort of the unidirectional layer. The matrix effort is calculated according to a micromechanical model considering thermal residual stresses. Particularly under transverse loading, the damage Evolution can be predicted as a function of the dilatational strain energy of the matrix. Using the concept of the matrix effort presented in this work, a prediction of the fatigue life of the investigated material at different ambient temperature conditions can be performed. T3 - BAM Dissertationsreihe - 169 KW - Ermüdung KW - Faser-Kunststoff-Verbund KW - GFK KW - Schädigung KW - Thermomechanik KW - Fatigue KW - Composite KW - Glas fibre reinforced polymer KW - Damage KW - Thermomechanics PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-530253 SN - 1613-4249 VL - 169 SP - 1 EP - 164 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-53025 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kraus, David A1 - Trappe, Volker T1 - Transverse damage in glass fiber reinforced polymer under thermo-mechanical loading JF - Composites Part C N2 - In this study, the thermomechanical damage behavior of a glass fiber reinforced polymer material is investigated. The coefficients of thermal expansion of the composite as well as the matrix are measured in a wide temperature range. Quasi-static experiments with neat resin, unidirectional and multidirectional laminates are performed as well as fatigue experiments in a temperature range from 213 K to 343 K. This study focusses on the matrix damage due to fiber-parallel loading. A correlation between matrix effort, the dilatational strain energy of the matrix and the damage state of the specimen is demonstrated. It is shown that a fatigue life assessment can be performed with the aid of a temperature-independent master fatigue curve. KW - Composite KW - Glass fiber reinforced polymer KW - Thermo-mechanics KW - Fatigue KW - Damage KW - Temperature PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-527462 DO - https://doi.org/10.1016/j.jcomc.2021.100147 SN - 2666-6820 VL - 5 SP - 100147 PB - Elsevier B.V. AN - OPUS4-52746 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ghafafian, Carineh A1 - Trappe, Volker T1 - Fully-reversed fatigue behavior of scarf joint repairs for wind turbine blade shell applications N2 - Due to manufacturing imperfections which can propagate to damage under in-service loads, wind turbine rotor blades, made primarily of glass fiber reinforced polymers (GFRP), often fail significantly before their design life. To enable a quick and cost-effective return to service, localized repairs can be executed by technicians in the field, directly accessing the blades by suspended roping. Scarf joint repairs, shown to be highly efficient with a smooth load transition across angled joint walls and a restored aerodynamic profile, are the focus of this study. The damage mechanisms of these structures were examined under fully-reversed mechanical cyclic loading with a load ratio R = -1, which was made possible on the coupon scale by a custom designed anti-buckling support. The number of cycles to failure were compared across load levels. While the scarf joint ratio was held constant at 1:50, known from industry and literature to be a good compromise between restored mechanical properties and repair size, the layup sequence was varied between small-to-large and large-to-small. Hereby the effect of the presence of resin pockets and fiber orientation mismatch between the parent and repair structure on the failure mechanism as well as fatigue strength of ±45° GFRP scarf joint repair structures was studied. Strain development across the joint length was measured to assess stiffness degradation in addition to the fatigue strength recovery of scarf joint structures with respect to pristine reference specimens. Grayscale analysis was used to monitor the damage state leading to fracture across the specimens. Post-mortem fractography analysis with light microscopy described the global failure mechanisms as well as local damage distribution within the structure, all of which provided insight to critical variables in scarf joint GFRP structures under fully-reversed mechanical cyclic loading, allowing for the tailoring of such repairs on wind turbine blade shells for maximum restoration of service life. T2 - 20th European Conference on Composite Materials (ECCM20) CY - Lausanne, Switzerland DA - 26.06.2022 KW - Glass fiber reinforced polymers KW - Scarf repairs KW - Fatigue PY - 2022 AN - OPUS4-55638 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lüders, C. A1 - Kalinka, Gerhard A1 - Li, Wei A1 - Sinapius, M. A1 - Wille, T. T1 - Experimental and numerical multiscale approach to thermally cycled FRP JF - Composite Structures N2 - Due to the different thermal expansion of the constituent materials, cyclic thermal loading of FRP induces alternating stresses in the material at two scales: at the micro scale (level of fibre–matrix-interaction) and at the macro scale (level of the multidirectional laminate). Especially the micro scale effect is not comprehensively investigated yet. Additionally, computational investigations mostly neglect this effect due to the homogenous modelling of the composite material. As this effect is assumed to significantly contribute to the fatigue of FRP at thermal loads, the present paper suggests an experimental and numerical multiscale approach including Experiments at the different involved material scales to separately observe the effects acting at these scales. The approach also includes numerical modelling for each scale to complement the knowledge gained from the Experiments and to create a basis for the consideration of the micro effect even in macroscopic fatigue models treating homogeneous modelled composites. The main focus of the contribution is to bring the overall Approach up for discussion, rather than to present the multiscale modelling details. KW - Fatigue KW - Thermal cycling KW - Fibre reinforced plastic KW - Cryogenic KW - Carbon Fibre KW - Epoxy Resin PY - 2020 DO - https://doi.org/10.1016/j.compstruct.2020.112303 SN - 0263-8223 VL - 244 SP - 112303 PB - Elsevier Ltd. CY - Niederlande AN - OPUS4-50844 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ghafafian, Carineh A1 - Popiela, Bartosz A1 - Nielow, Dustin A1 - Trappe, Volker T1 - Restoration of structural integrity – Repairs for wind turbine blade shells N2 - Wind turbine rotor blade shells are manufactured as sandwich structures with fiber-reinforced polymer (FRP) due to the material’s high specific stiffness and strength. With a growing renewable energy industry and thereby a spread of wind energy farms, especially in offshore applications, the need to fully utilize turbines through their designed lifespan is becoming increasingly essential. However, due to imperfections during manufacturing, which are then propagated by harsh environmental conditions and a variety of loads, blades often fail before their projected lifespan. Thus, the need for localized repair patch methods for the outer shell portions of the blades has become of greater interest in recent years, as it is crucial to the optimal compromise between continuation of wind energy production, cost efficiency, and restoration of structural performance. To increase the understanding of the effect on the fatigue life of the rotor blades, this study tests localized repair patch methods and compares them to each other as well as to reference, non-repaired specimens. Manufactured with the vacuum-assisted resin infusion process, the shell test specimens are produced as a curved structure with glass FRP sandwiching a polyvinyl chloride foam core to best represent a portion of a rotor blade shell. Patch repairs are then introduced with varying layup techniques, and material properties are examined with cyclic fatigue tests. The intermediate scale test specimens allow for the observation of material as well as structural variables, namely of interest being the stiffness and strength restoration due to the repair patches. Damage onset, crack development, and eventual failure are monitored with in-situ non-destructive testing methods to develop a robust understanding of the effects of repair concepts. T2 - 5th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures CY - Potsdam, Germany DA - 27.08.2019 KW - Wind turbine blade shells KW - Fiber reinforced polymers KW - Sandwich structures KW - Fatigue PY - 2019 AN - OPUS4-48859 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ghafafian, Carineh A1 - Trappe, Volker T1 - Restoring structural integrity - localized repairs for wind turbine rotor blades N2 - The effect of localized repairs on the mechanical properties and thus the lifespan of wind turbine rotor blade shells is examined. T2 - SAMPE Symposium 2019 CY - Dresden, Germany DA - 06.02.2019 KW - Fatigue KW - Glass fiber reinforced polymers KW - Lightweight materials KW - Sandwich KW - Wind turbine blades PY - 2019 AN - OPUS4-47443 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -