ABSTRACT
One attractive feature about stretch control is the fact that people can use it to measure residual preloads long after the fastener has been tightened. Every dimension on a fastener is, of course, subjected to manufacturing variation or tolerance, even for something as highly standardized as a bolt. One way to determine the theoretical scatter in preload would be to introduce the maximum and minimum dimensions into the stretch-preload equation. The actual situation is better analyzed by statistical methods. The dimensional variations discussed so far dealt with room temperature variations, that is manufacturing tolerances. If the bolts and joint members are made from dissimilar materials, or are at different temperatures, then the problem of relating bolt stretch to bolt tension becomes more complicated. Coarser dimensional differences, such as in the fit between nut and bolt threads, can have a still larger effect on stress distribution.
