Numerical and experimental failure analysis of wind turbine blade fastener

The objective of this study is to conduct a root cause failure analysis on wind turbine fasteners constructed from carbon steel Grade 10.9. The presence of corrosion pits at the thread root, as well as beach and ratchet marks on the fracture surface, suggests that the fastener failed due to a corrosion-fatigue mechanism. The microstructure of the failed fastener predominantly consisted of 98 % tempered martensite, with some bainite and a small amount of chromium carbides, which is characteristic of quenched and tempered low alloy steel. Magnetic particle testing revealed similar crack marks on other fasteners in similar locations, indicating the points of maximum stress in these fasteners. Furthermore, finite element analysis using Abaqus software demonstrated that for a corrosion pit to grow, it required a minimum pit length and depth of 0.5 mm and 0.6 mm, respectively.