ABSTRACT
The key to this analysis is understanding the dimension for gasket relaxation R. As load is applied to the fastener, the gasket and joint sections are compressed and the bolt is stretched. When the desired preload is reached, the gasket material will have a given thickness (equal to the distance between the inside faces of the joint sections). This dimension will change over time due to many phenomena such as elastic interactions, gasket creep, and differential thermal expansion. (The dimension normally becomes smaller because most of these phenomena rob the fastener of preload.) The amount by which the gasket thickness decreases is R. Note that R is on the fastening system side of the joint diagram (Fig. 10). This is because as the faces of the joint move together by the dimension R, the fastening system is unloaded. Since R is strictly a change in dimension, it should have no effect on the slope of the diagram. It is as if the point of origin of the fastening system side of the diagram has "slipped" or moved by R. The entire joint diagram becomes smaller, resulting in a lower residual preload. Preload lost is strictly a function of the amount of the relaxation and the spring rate of the fastening system.
