The bolt pretightening fasteners, the role of fatigue fracture

Fasteners, played a very important role in engineering structures, such as aerospace, infrastructure, civil, automobile and other industries. Fastener failure could lead to catastrophic consequences and major financial losses. One of the most common fastener failure mode is the fatigue cracking. Inadequate design considerations, the material problem, insufficient of pre-tightening force, loose and too much can cause fastener fatigue load. Similar to other metal parts, fasteners, failure including the overload, corrosion cracking, embrittlement, creep and fatigue. Due to external load, fasteners, overload may occur in the process of installation or use. Fasteners overload failure investigation should include the evaluation of materials performance, main purpose is to determine the cause of the reasons for damage of the fasteners, such as the strength of the fastener and the load imposed on the fasteners. In some common stress corrosion cracking and hydrogen embrittlement in metals, when the fasteners in the process of serving under static stretching, it is also important for fastener failure mode. In the light of the fastener is expected to stress, material and environment must be carefully considered, with the appropriate to reduce the stress corrosion cracking and hydrogen embrittlement. In the process of plating, hydrogen is likely to spread into fasteners, resulting in the hydrogen embrittlement. In order to reduce the hydrogen embrittlement of the susceptible materials, fasteners must be carried out in addition to the hydrogen treatment. Fatigue is the most common form of fracture in the metal structure, accounting for 80% of the fracture. Fasteners is not exceptional also, fatigue fracture reason is also the most common fasteners. When cycle load exceeds the fatigue strength of the material, when loaded enough cycles, the fatigue crack initiation and propagation in the fastener. Fastener material, geometry and stress amplitude, mean stress and assembly parameters will affect the fatigue performance. Fastener assembly process is the most important, but often overlooked when analyses its fracture reason, it is also the primary sources of fastener fatigue fracture. Fracture of the bolt fasteners