What are the primary reasons for bolts becoming loose?

What are the primary reasons for bolts becoming loose?

Facing encountered studs mainly the broken ones or bolts are one of the least pleasant sights that you can think of. This is all the more so when you work on mechanical equipment or automobiles as per the view point of bolt cutter equipment suppliers. Most of us would have tried a host of methods to remove broken bolts from the metal bolts of the garage pipes to the cylindrical protector found in the motor bikes. To cut one there is the presence of a high quality bolt cutter. Methods in the form of welding and drilling are available on the internet worldwide in response to broken bolts. But the real question that arises is what causes the bolts to break

Over stressing

The word over stress really explains the rationale behind this logic. But there does appear more to it. With a load there are three facets that a bolt experiences. The first is the preload, then the service load and last happens to be tensile load. In case of preload it appears to be the internal stress, which is known to keep the two joint materials intact whereas the service load connotes the external factors that cause the Joint materials to churn in separated stresses. The tensile load means that both sides refer to a static stress that is being put on both sides of the bolt in a separate manner. If you tighten and overturn the bolt on a regular basis is going to increase the tensile load of the bolt. If this load goes on to exceed the tensile strength then permanent damage to the bolt could emerge. You need to figure out the exact amount of torque that is applicable to the bolt as then chances of over stress are remote.


Nearly 90 % of bolt breaking cases are due to excess fatigue. Any bolts especially the shear bolt is designed to fall in due course of time. What it means is that there efficiency is not going to last for a lifetime. This can be illustrated if you go back to the service load and the preload.  Every bolt experiences a cycle of preload along with service load. You figure out the fatigue by the number of load cycles a bolt can withstand. For this reason most equipment manuals do suggest replacement of bolts after a year or so. All the more so when the bolt is exposed to constant stress such  as those on stamping machines and modelling equipment.


Corrosion in short refers to the impact that is created by external factors or exposure to compatible metal parts. For example the bolts near the engine of the vehicle may require engine fluids and oil leaks. With the passage of time the chemicals would force the bolts to deteriorate and this is chemical corrosion.

To conclude among the three cases fatigue does appear to be the main cause of  broken bolt causes. Timely inspection can prevent it.


Please enter your comment!
Please enter your name here