TY - CONF A1 - Trappe, Volker A1 - Nielow, Dustin T1 - Fatigue loading of sandwich shell test specimens with simulated production imperfections and in-situ NDT N2 - A shell test bench was developed at BAM 5.3 which allows for static and fatigue testing of curved fiber-reinforced plastic (FRP) structures, during which in-situ the damage state can be non-destructively inspected by thermography and strain-field measurement techniques. Sandwich shell specimens with typical wind turbine blade manufacturing defects were designed and tested. The tested imperfections show a fairly significant reduction (up to 90%) of the shell test specimens‘ lifetime, depending on the type of imperfection. Using the in-situ NDT methods incorporated in the shell test bench, the location and cycle time of the initial defects and the damage evolution was investigated. T2 - 7. International Conference on Fatigue of Composites CY - Vicenza, Italy DA - 04.07.2018 KW - Fatigue of sandwich shell structures KW - Non-destructive testing KW - Wind turbine blades PY - 2018 AN - OPUS4-50126 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Trappe, Volker A1 - Nielow, Dustin T1 - Fatigue loading of sandwich shell test specimens with simulated production imperfections and in-situ NDT N2 - A shell test bench was developed at BAM 5.3 which allows for static and fatigue testing of curved fiber-reinforced plastic (FRP) structures, during which in-situ the damage state can be non-destructively inspected by thermography and strain-field measurement techniques. Sandwich shell specimens with typical wind turbine blade manufacturing defects were designed and tested. The tested imperfections show a fairly significant reduction (up to 90%) of the shell test specimens‘ lifetime, depending on the type of imperfection. Using the in-situ NDT methods incorporated in the shell test bench, the location and cycle time of the initial defects and the damage evolution was investigated. T2 - 7. International Conference on Fatigue of Composites CY - Vicenza, Italy DA - 04.06.2018 KW - Fatigue of sandwich shell structures KW - Non-destructive testing KW - Wind turbine blades PY - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-501275 SP - 1 EP - 7 AN - OPUS4-50127 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ghafafian, Carineh A1 - Trappe, Volker A1 - Nielow, Dustin T1 - Analysis of the fatigue strength of various repair concepts for wind turbine rotor blades N2 - High-performance composites, including glass-fiber reinforced plastic (GFRP) materials, are favored as a construction material for wind turbine rotor blades due to their high specific strength and stiffness properties. During the manufacturing process, however, imperfections are often introduced, then further propagated due to harsh environmental conditions and a variety of loads. This leads to failure significantly before their projected 20-year lifespan. As replacement of entire blades can be a costly potential outcome, localized repair of the damaged region to restore structural integrity and thus lengthen its lifespan has become an important issue in recent years. Rotor blades are often repaired using a common technique for composite laminates: adhesively bonded structural repair patches. These methods involve replacing the lost load path with a new material that is joined to the parent structure, and include scarf or plug repairs. However, there currently do not exist any standardized repair procedures for wind turbine rotor blades, as comparisons of blade properties repaired with the existing methods have not been studied in depth. Namely, there is a lack of understanding about the effects of various repair methods on the fatigue life of the shells of rotor blades. This study therefore aims to begin to fill this knowledge gap by testing the influence of different repair patches on the blades’ mechanical properties. Manufactured with the vacuum-assisted resin infusion process, the test specimens are produced as a curved structure with GFRP sandwiching a polyvinyl chloride foam core to best represent a portion of a rotor blade shell. Scarf repairs are then introduced with varying layup techniques, and material properties are examined with cyclical fatigue tests. Crack growth and development is monitored during fatigue testing by various non-destructive testing methods, including passive thermography with an infrared camera system, and a 3D deformation analysis system with ARAMIS. Large deformation fields and detection of in- and out-of-plane deformations is thus possible in-situ. The mechanical behavior and development of defects in the various repaired specimens is compared to each other as well as to reference test specimens with no repair patches. In-situ test data is combined with further non-destructive testing methods, including laminography, and active thermography, to develop a robust understanding of the effects of repair concepts. T2 - MSE Congress 2018 CY - Darmstadt, Germany DA - 26.09.2018 KW - Glass fiber reinforced polymers KW - Lightweight materials KW - Fatigue of sandwich structures KW - Wind turbine blades KW - Sandwich PY - 2018 AN - OPUS4-46102 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 – a comparison of various repair concepts for wind turbine rotor blade shells N2 - Localized patches are a cost- and time-effective method for repairing fiber-reinforced polymer (FRP) sandwich wind turbine rotor blade shells. To increase the understanding of their effect on the fatigue of the blades, this study examines the effect of various layup methods of localized repair patches on the structural integrity of composite sandwich structures. Manufactured with the vacuum-assisted resin infusion (VARI) process, the shell test specimens are produced as a curved structure with glass fiber reinforced polymer (GFRP) sandwiching a polyvinyl chloride (PVC) foam core. Patch repairs are then introduced with varying layup techniques, and material properties are examined with cyclic fatigue tests. The transition region between patch and parent material is studied in greater detail with finite element method (FEM) simulations, with a focus on the effect of fiber orientation mismatch. 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 on material stiffness and strength. T2 - SMAR 2019 - 5th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures CY - Potsdam, Germany DA - 27.08.2019 KW - Lightweight materials KW - Glass fiber reinforced polymers KW - Sandwich KW - Wind turbine blades PY - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-482170 SP - 1 EP - 8 PB - German Society for Non-Destructive Testing (DGZfP e.V.) AN - OPUS4-48217 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 - TY - CONF A1 - Trappe, Volker A1 - Ghafafian, Carineh T1 - Scarf-joint repairs under fatigue loading investigated for sandwich shell applications N2 - Wind turbine rotor blades are produced as aerodynamic, three-dimensionally formed sandwich shell structures using mainly glass fiber reinforced plastics (GFRP). The GFRP used today have the potential to withstand the harsh operating conditions of rotor blades over the projected service life of 20 years. Premature damages that occur can be traced primarily back to design and/or manufacturing imperfections, as well as unusually high load scenarios (for instance lightning strikes, or strong winds combined with system control errors). Therefore, rotor blades have to be repaired several times (on average 2-3 times) during their projected service life. Approximately 70% of these are repairs of small- to medium-sized sandwich shells, carried out by technicians directly accessing the blade by suspended roping at the wind turbine location. The goal is to execute repairs that will last over the remaining service life, i.e. be sustainable. Within the framework of a research project carried out at BAM, Division 5.3 Polymer Matrix Composites, Department 5 for Materials Engineering, not only was the geometric shape (round vs. square in relation to the top view) varied, but also the layup of the scarf repair structure, variables that have not been studied systematically to-date. Sub-component scale sandwich shell specimens with representative repairs were used in this work in addition to coupon-scale specimens that are more commonly seen in literature. These sub-component shell specimens were tested using a unique shell test bench under loading conditions representative of wind turbine blade shell operating conditions with respect to fatigue strength. Using non-destructive testing methods (field strain measurement and thermography), damage development and distribution was monitored and analyzed in-situ. As a result, a concept was developed in which the repaired areas showed at least equivalent if not higher fatigue strength than the reference shells that were not repaired. T2 - ICFC9 - The 9th International Conference on the Fatigue of Composites CY - Vicenza, Italy DA - 21.06.2023 KW - Repair of sandwich shell structures KW - Non-destructive testing KW - Wind turbine blades PY - 2023 AN - OPUS4-57929 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -