Encountering broken studs or bolts is one of the most unwanted scenarios we can think of, especially, when working on automobiles and other mechanical equipment. Many people have tried to develop different methods to remove any broken bolt from their properties ranging from the cylindrical protector of their motorbike carburetor up to the metal plates of their garage doors. Methods such as drilling and welding are now available all over the internet in response to the increasing cases of broken bolts.
The real question is: “What causes a broken bolt?“
1. Over-stressing
The word ” over-stress” is already enough to understand this cause; however, there is more to it than that. There are 3 kinds of load the bolt experiences: the preload, the service load, and the tensile load. The preload refers to the internal stress which keeps the two joint materials intact while the service load refers to the external factors causing the joint materials to exert separated stresses. The tensile load, on the other hand, refers to a static stress pulling both ends of the bolt separately. Tightening and overturning the nut regularly will increase the tensile load of the bolt. If the tensile load exceeds the tensile strength, then, the bolt will gain permanent damage which causes it to break. Determining the appropriate amount of torque applicable to specific types of bolt is necessary to avoid over-stressing.
2. Fatigue
About 85% of all broken bolt cases is due to fatigue. All bolts, especially the shear bolts, were designed to fail in due time. In other words, their efficiency is not for a lifetime. This can be explained by going back to the preload and service load. Every bolt or stud experiences a cycle of preload and service load. Fatigue is then determined by how many load cycles a bolt can withstand. This is why most equipment manuals would suggest bolt replacements after a year or two, especially, when the bolt is frequently exposed to stressing factors such as those on modeling equipment and stamping machines.
3. Corrosion
Corrosion, on the contrary, refers to the effects brought about by external elements such as excreted chemicals from nearby parts or exposure to incompatible metal components. For instance, bolts near the vehicle’s engine may acquire oil leaks and other engine fluids. These chemicals will cause the bolt to deteriorate as time passes by – that is the chemical corrosion.
Another kind of corrosion is when the bolt was used to join incompatible metal components. Because of incompatibility, the bolt deteriorates and might break as well. This is what we call the galvanic corrosion. Although corrosion is one of the primary causes of broken bolts, it is still a rare case and can only be found in advanced metal industries like in mechanical engineering, mining, and construction.
Among these three, fatigue comprises the majority of broken bolt cases followed by over-stressing. Corrosion varies from situations and is rarely to happen. Keeping these factors in mind will help you maintain the efficiency of your equipment by preventing bolts from breaking.