The anti-loosing performance and the reduction of stress concentration of bolts and nuts which have slight pitch difference

为提高螺栓螺母的抗松脱性能和疲劳强度，对不同螺距差的螺栓螺母进行了松脱和疲劳试验。讨论了节距差抗松脱性能和疲劳强度的最佳条件。为了提高防松性能，最理想的螺距差是α = α-中。为了提高疲劳寿命，最理想的螺距差是alpha=alpha-small。尽管如此，疲劳极限没有得到改善。在这两种情况下，有限元方法被用来模拟松动和疲劳实验。最后，用有限元方法讨论了大缺口根部半径对裂纹扩展的影响。结果表明，大缺口根部半径螺栓和螺母的疲劳强度得到了提高。

In this paper, to improve anti-loosing performance and fatigue strength of the bolts and nuts, the loosening and fatigue experiments are performed with varying the pitch difference. Then, the most desirable conditions for the anti-loosing performance and fatigue strength of the pitch difference are discussed. To improve anti-loosing performance, the most desirable pitch difference is alpha=alpha-middle. To improve fatigue life,the most desirable pitch difference is alpha=alpha-small. Although, the fatigue limit is not improved. In the both case, the finite element method is applied to simulate the loosening and fatigue experiment. Finally, the effect of the large notch root radius is discussed by using FEM. It is found that, the fatigue strength of large notch root radius bolts and nuts is improved.