曲げが作用するボルト/ナット結合体の疲労強度

（曲げ応力がボルトの疲労強度に及ぼす影響）

抄録

The bolt/nut assemblies in multi-bolted joints are subjected to bending moment as well as the tensile force. On the other hand, the fatigue strength of a bolt in bolt/nut assemblies is basically determined from fatigue tests under purely tensile loading assuming that bending moment acts simply to give additional tensile stress on the first thread root. The effect of the bending moment on the fatigue strength of a bolt, however, has not yet been investigated in detail. To clarify this, the fatigue testing jigs by which the tensile force/bending moment ratio can be controlled in the fatigue tests were developed using 3D FE analysis with simple solid bolt/nut model. The fatigue strength of a bolt subjected to bending is much higher than that estimated by the above-mentioned assumption, and the testing jigs failed during fatigue test. In this report , the effect of bending moment is considered from the analysis for the fatigue strength of jigs as a index. Finally, it was found that the difference in a stress area and the thread cross section obtained from the theoretical equation is one of the reason for under estimation of the fatigue strength.