It is very difficult to maintain the specified fatigue strength of high-strength bolts other than the reduction of the lead on the bolt threads such as specified in Military Standard Bolt MS21250 in which high strength and high fatigue are required. However, reduction of the lead on external threads increases the functional pitch diameter, which could result in the functional pitch diameter exceeding the limit of the dimensional requirement. To maintain fatigue life within the range of the dimensional requirements, it is necessary to evaluate quantitatively the effect of lead reduction on the fatigue life. To this end, I have proposed the mathematical model of load pass on external threads with a reduced lead. Fatigue life results estimated from this mathematical model have shown themselves to be in good agreement with the relative experimental fatigue data. This article discusses the relationship of dimensional and fatigue strength requirements on high-strength bolts, and attempts to determine, using the mathematical model, the dimensions compatible with fatigue strength in order to facilitate GO and NOT GO thread inspection methodologies.
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