When a bolt is tightened, the bolt is stretched. As the bolt is stretched, the clamping force increases.
Different steel can be stretched to different lengths until they brake. How do steels stretch? In the first stages of stretching the steel is elastic, meaning if the steel is stretched in this area, it will return to it's original shape. If it is stretched further, it becomes non-elastic and the metal will not return to its original shape. This happens if bolts are over tightened. Once the bolt has been over stretched it has to be replaced.
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