Pre-tightening Force For Fatigue Fracture Of Bolt Fasteners

Similar to other metal parts, fastener failures include overload, corrosion-related cracking, embrittlement, creep and fatigue. Due to external loads, fastener overload may occur during installation or use.

The investigation of fastener overload failure should include the evaluation of material performance, the main purpose is to determine the cause of fastener damage, such as the strength of the fastener and the load imposed on the fastener.

Stress corrosion cracking or hydrogen embrittlement, which is common in some metals, is also an important failure mode for fasteners when they are subjected to static tension during service.

In view of the expected stresses of fasteners, materials and environments must be carefully considered to appropriately mitigate stress corrosion cracking or hydrogen embrittlement.

During the electroplating process, hydrogen is likely to diffuse into the fastener, causing hydrogen embrittlement. In order to reduce hydrogen embrittlement of susceptible materials, fasteners must be treated with hydrogen removal.

Fatigue is the most common form of fracture in metal structures, accounting for 80% of fractures. Fasteners are no exception. Fatigue is also the most common cause of fracture.

When the cyclic load exceeds the fatigue strength of the material, when it is loaded for a sufficient period of time, fatigue cracks will initiate and propagate on the fastener. Fastener material, geometry, stress amplitude, average stress and assembly parameters all affect fatigue performance.

The fastener assembly process is the most important, but it is often overlooked when analyzing the cause of its fracture. It is also the main source of fastener fatigue fracture.