Failure analysis study on a fractured bolt

Abstract The aim of this work is the determination of the cause of a bolt fracture. The group was formed by a screw and a castellated self-braking nut with a plastic brake. Chemical, mechanical and microstructural material characterizations were carried out, fulfilling all material specifications. A microscopic observation revealed fatigue striations, which are typical signs of a progressive fracture. The fracture has been produced in the penultimate thread, one of the most critical zones of the screw. Hydrogen embrittlement also could have occurred, decreasing the fatigue resistance of the screw, but also its life of service.