Details

Autor(en) / Beteiligte

• Ghafafian, Carineh

Titel

Investigation of the Failure Mechanisms of Scarf Repairs on Glass Fiber Reinforced Polymer Shell Structures

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2023

Link zum Volltext

• ProQuest

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Wind turbine blades often fail significantly before their design life. As a cost- and time-effective alternative to replacing entire blades, repairs can be executed by technicians on suspended roping directly accessing blades in the field. There is, however, no generally accepted practice for such localized repairs, and methods as well as material property restoration are not fully understood to-date. Due to their restored property efficiency, the failure mechanisms of scarf joints are taken into focus in this work for an in-depth understanding of how to better tailor localized blade repairs.In the scope of this work, a multi-level, systematic experimental approach is taken for an application-oriented problem. The influence of fiber orientation mismatch, scarf joint layup and repair geometry on glass fiber reinforced polymer (GFRP) shell structures is examined. Failure mechanisms of the scarf joint structure are compared to reference specimens without a repair under quasi-static as well as fully-reversed cyclic fatigue loading conditions for biaxial GFRP laminates as monolithic coupon specimens as well as curved sandwich shell specimens on the intermediate scale.A scarf joint is shown to introduce stiffness discontinuities in the joint interface when interrupting load-carrying fibers, affecting the fracture front propagation path and thereby failure mechanism and in turn the overall restored ultimate tensile strength. Resin pockets in the joint interface region of a small-to-large layup are shown to have a positive influence on the structural integrity if no load-carrying fibers are disrupted by the presence of the scarf joint due to a localized yielding effect, by which the resin pockets in the joint interface are able to alleviate stresses in the structure. The repair geometry, however, namely the lack of sharp corners, is shown to have a greater influence on the restored fatigue performance than the scarf joint layup. Additionally, a fatigue-superior repair material is shown to improve the overall fatigue performance of the joint structure due to a redistribution of strain by varying damage distribution across the structure in the form of inter-fiber failure.The overall good agreement of tendencies on the coupon and intermediate scale in this work as well as the ability to test numerous adherend combinations on the coupon scale lead to the ability to focus future repair testing on the coupon scale for material and joint interface effects for a more cost- and time-saving approach.