DEVELOPMENT OF DESIGN CHARTS FOR BOLTS PRELOADED UP TO THE PLASTIC RANGE.

From the mathematical formulation of the tightening process, a diagram was developed which enables the determination of the necessary tightening torque, for a certain bolt, to induce the maximum utilizable preload in bolt. The coefficients of friction between threads and under nut could be determined with the aid of an apparatus which also allows the study of the effect of the different parameters affecting friction such as material and surface conditions. It is of interest to notice that for each bolt and coefficient of friction under nut, there is a critical value for the thread coefficient of friction at which the required tightening torque attains a maximum value. The charts are constructed with the following ranges for the coefficients of friction: mu //r prime up to 0. 5 and mu //n up to 0. 3.