Abstract
This study aims to confirm the effect of incomplete thread of nut on the local stress acting on the bolt thread root which may affect the fatigue strength of a bolt. However, the local stress acting on the bolt thread root cannot be obtained with sufficient accuracy by 3-D FEM for bolt-nut assembly due to the constraint of the numbers of nodes and elements. Therefore, a method is proposed in which 3-D helical model for bolt with two or three threads is analyzed. The boundary conditions on the helical model are determined by using the calculated results for 3-D bolt assembly model with fewer elements without root radius. First, 2-D FE analyses were performed for bolt-nut assembly with root radius having sufficient numbers of elements, and for bolt-nut assembly without root radius with fewer elements, respectively to examine the effect of the root radius on the boundary conditions including the load distributions on the mating threads. The analytical results for two thread (IP) model obtained from bolt-nut assembly model without root radius show fairly good agreement with that for bolt-nut assembly model with sufficient elements. Then, the method was applied to 3-D bolt-nut model with helical angle. Finally, it was clarified that the incomplete thread of nut may affect significantly on the local stress acting on the bolt thread root which determine the fatigue strength.
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