TY - THES A1 - Nielow, Dustin T1 - Einfluss fertigungsbedingter Imperfektionen auf die Schwingfestigkeit von FKV-Schalenstrukturen in Sandwichbauweise 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 U6 - http://nbn-resolving.de/urn/resolver.pl?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 - Gaal, Mate A1 - Schadow, Florian A1 - Nielow, Dustin A1 - Trappe, Volker T1 - Air-coupled ultrasonic ferroelectret transducers with additional bias voltage for testing of composite structures N2 - Common air-coupled transducers for non-destructive testing consist of a piezocomposite material and several matching layers. Better acoustical matching to air is achieved by transducers based on charged cellular polypropylene (PP). This material has about hundred times lower acoustic impedance than any piezocomposite, having about the same piezoelectric coefficient. The piezoelectric properties of cellular PP are caused by the polarization of air cells. Alternatively, a ferroelectret receiver can be understood as a capacitive microphone with internal polarization creating permanent internal voltage. The sensitivity of the receiver can be increased by applying additional bias voltage. We present an ultrasonic receiver based on cellular PP including a high-voltage module providing bias voltage up to 2 kV. The application of bias voltage increased the signal by 12 to 15 dB with only 1 dB increase of the noise. This receiver was combined with a cellular PP transmitter in through transmission to inspect several test specimens consisting of glass-fiber-reinforced polymer face sheets and a porous closed-cell PVC core. These test specimens were inspected before and after load. Fatigue cracks in the porous PVC core and some fatigue damage in the face sheets were detected. These test specimens were originally developed to emulate a rotor blade segment of a wind power plant. Similar composite materials are used in lightweight aircrafts for the general aviation. The other inspected test specimen was a composite consisted of glass-fiber-reinforced polymer face sheets and a wooden core. The structure of the wooden core could be detected only with cellular PP transducers, while commercial air-coupled transducers lacked the necessary sensitivity. Measured on a 4-mm thick carbon-fiber-reinforced polymer plate, cellular PP transducers with additional bias voltage achieved a 32 dB higher signal-to-noise ratio than commercial air-coupled transducers. T2 - 10th International Symposium on NDT in Aerospace CY - Dresden, Germany DA - 26.10.2018 KW - Airborne ultrasonic testing KW - Air-coupled ultrasonic testing KW - Ferroelectret KW - Composites KW - Rotor blade PY - 2018 AN - OPUS4-46656 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Schadow, Florian A1 - Nielow, Dustin A1 - Trappe, Volker T1 - Air-coupled ultrasonic ferroelectret transducers with additional bias voltage for testing of composite structures N2 - Common air-coupled transducers for non-destructive testing consist of a piezocomposite material and several matching layers. Better acoustical matching to air is achieved by transducers based on charged cellular polypropylene (PP). This material has about hundred times lower acoustic impedance than any piezocomposite, having about the same piezoelectric coefficient. The piezoelectric properties of cellular PP are caused by the polarization of air cells. Alternatively, a ferroelectret receiver can be understood as a capacitive microphone with internal polarization creating permanent internal voltage. The sensitivity of the receiver can be increased by applying additional bias voltage. We present an ultrasonic receiver based on cellular PP including a high-voltage module providing bias voltage up to 2 kV. The application of bias voltage increased the signal by 12 to 15 dB with only 1 dB increase of the noise. This receiver was combined with a cellular PP transmitter in through transmission to inspect several test specimens consisting of glass-fiber-reinforced polymer face sheets and a porous closed-cell PVC core. These test specimens were inspected before and after load. Fatigue cracks in the porous PVC core and some fatigue damage in the face sheets were detected. These test specimens were originally developed to emulate a rotor blade segment of a wind power plant. Similar composite materials are used in lightweight aircrafts for the general aviation. The other inspected test specimen was a composite consisted of glass-fiber-reinforced polymer face sheets and a wooden core. The structure of the wooden core could be detected only with cellular PP transducers, while commercial air-coupled transducers lacked the necessary sensitivity. Measured on a 4-mm thick carbon-fiber-reinforced polymer plate, cellular PP transducers with additional bias voltage achieved a 32 dB higher signal-to-noise ratio than commercial air-coupled transducers. T2 - 10th International Symposium on NDT in Aerospace CY - Dresden, Germany DA - 26.10.2018 KW - Airborne ultrasonic testing KW - Air-coupled ultrasonic testing KW - Ferroelectret KW - Composites KW - Transducers PY - 2018 SP - 1 EP - 6 AN - OPUS4-46657 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Miliūtė, Aistė A1 - George, Janine A1 - Mieller, Björn A1 - Stawski, Tomasz T1 - ZrV2O7 negative thermal expansion (NTE) material N2 - Zirconium vanadate (ZrV2O7) is a well-known negative thermal expansion (NTE) material that exhibits significant isotropic contraction over a broad temperature range (~150°C < T < 800°C). Therefore, it can be used to create composites with controllable expansion coefficients and prevent thermal stress, fatigue, cracking, and deformation at interfaces. We implement interdisciplinary research to analyze such material. We study the influence of the synthesis methods and their parameters on the sample's purity, crystallinity, and homogeneity. Moreover, we implement ab initio-based vibrational computations with partially treated anharmonicity in combination with experimental methods to follow temperature-induced structural changes and rationalize the negative thermal expansion in this material, including the influence of the local structure disorder. T2 - SALSA Make and Measure Conference CY - Berlin, Germany DA - 13.09.2023 KW - NTE KW - Composites KW - TEM PY - 2023 AN - OPUS4-58367 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -