Investigating Core Gaps and the Development of Subcomponent Validation Methods for Wind Turbine Blades: Paper No. AIAA 2020-0493

Core gaps are a common manufacturing defect observed in wind blade composite sandwich constructions, which occur when sheets of core material are not properly adjoined in the mold. The aim of this study was to characterize core gaps in composite sandwich constructions at the coupon scale to gain an initial understanding of the defect before developing appropriate methodologies for more complex subcomponents as part of a much broader wind blade structural validation and damage tolerance program. Long beam flexure in 4-point-bending was chosen as the most appropriate loading scenario. Beam specimens were characterized with and without 10 mm core gaps in fiberglass/balsa sandwich beams. The core gaps were characterized with two different resin systems: a Hexion epoxy and Arkema’s Elium resin system (a novel, infusible thermoplastic). Results showed that the Elium beams without the core gaps had a 15% lower static strength than their epoxy counterparts. The introduction of the core gap to the epoxy beams reduced their static strength by 35%. The Elium beams, however, exhibited negligible strength reductions with the inclusion of the core gap, but did show a notable change in failure mechanism. Overall, this characterization study provided pertinent information with regards to core gaps as a manufacturing defect to allow for continued development of damage tolerance and subcomponent validation methodologies with the inclusion of manufacturing defects.