Analysis of Six Hexagon Head Bolt Fracture

A broken bolt was analyzed by macro analysis, chemical composition analysis, mechanical properties testing,fracture analysis, metallographic analysis and hardness testing, the results show that the bolt is unidirectional bending fatigue fracture at surface of thread boot. It is mix fracture of transcrystalline and a few intergranular rupture in initiation zone. In extension zone it is transcrystalline fatigue fracture. The bolt splitting process is influenced by the bending fatigue stress and hydrogen, the bending stress is slight when the bolt broken. The main reasons for bolt fatigue rupture are higher remain H after zinc plating and vibration in working process.