Bolt loosening analysis is typically done during the design phase of building a structure. It also helps in identifying different factors that can lead to bolt slippage and provides suggestions on how to prevent it from happening or detect it early enough for remedial measures to be taken. Below are the reasons that lead to bolt loosening.
Under Tightening
An under-tightened bolt is loose and has no strength to hold the sections and the joints together. Due to lack of clamp force, there is sideway slippage between the sections. This causes unnecessary shear stress on a bolt which can cause it to break.
Vibrations
Bolted joints have a transverse motion when put under vibration. This motion causes parallel movement of the bolt head and the nut. The repeated movement of the two causes friction between the bolt and joint threads holding the sections together. These vibrations cause the bolt to unwind and lose its clamp force.
Differential Thermal Expansion
In bolt loosening analysis, differential thermal expansion of the material is an important factor. The difference in thermal expansivity of the bolt and joints is mainly due to environmental conditions or industrial processes. This causes the bolt material to expand and contract rapidly. This rapid thermal activity causes the bolt to loosen or break.
Shock
One of the most significant risks of industrial machinery is that it can cause a sudden and potentially dangerous shock. These shocks occur when a dynamic or alternating load is applied to the bolt or the joint, causing the bolt threads to slip relative to each other. This slippage causes the bolt to lose its clamp force and finally loosen.
