This paper studies thread-root fatigue of M3–M160 904L stainless steel hex bolts applied to automotive brackets and chassis structures. Focusing on typical field failures where cracks initiate at the first engaged thread under road vibration, the load path of threaded connections is analysed. Five principal failure mechanisms are identified, and a mechanism-driven validation workflow, evidence matrix and engineering checklist are constructed. The study confirms that material designation and nomi

This article studies bolt preload retention of 904L stainless steel hex bolts (M3–M160) used for wind turbine support structures under cyclic wind loads. Starting from field joint failure cases involving settlement and interface opening, an elastic joint mechanical model is adopted to analyse load redistribution. Five core failure mechanisms are elaborated, including interface separation, thread fatigue, bolt head fillet bending, fretting loosening and concealed corrosion. A mechanism-based vali