Abstract Due to its strength advantage, high strength bolts are able to provide larger clamping force. However, the changing behavior of friction coefficient during repeated tightening will adversely affect the tightening torque - clamping force relationship. To ensure reliable clamping force of high strength bolts, an easy implement experimental method to investigate the changing behavior of friction coefficient is put forward in this work. The constraint torque of bolt head, as well as the tightening torque and clamping force, was measured during tightening. Friction coefficient interval of bolt underhead is obtained according to the preset assumptions and experimental results. Based on the mechanical equilibrium relationship of the bolt during tightening, thread reaction torque can be obtained to calculate the friction coefficient of threads and bearing surface. Three cases are considered, namely without lubricant, lubrication at threads and nut surface. Statistical analysis was carried out through replicated experiments to investigate the effect of clamping force on the changing behavior of friction coefficient. Without lubrication, repeated tightening caused the increasing of friction coefficient, which resulted in a reduction of clamping force. When using a lubricant, it can protect the contact surface, and the obtained clamping force during repeated tightening was more stable. Experimental results showed that the proposed method can be used to investigate the changing behavior of friction coefficient during repeated tightening.

中文翻译：

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反复拧紧时高强度螺栓摩擦系数的变化行为

摘要 由于其强度优势，高强度螺栓能够提供更大的夹紧力。然而，反复拧紧过程中摩擦系数的变化行为将对拧紧扭矩-夹紧力的关系产生不利影响。为确保高强度螺栓可靠的夹紧力，本文提出了一种易于实施的实验方法来研究摩擦系数的变化行为。在拧紧过程中测量螺栓头的约束扭矩，以及拧紧扭矩和夹紧力。根据预设的假设和实验结果得到螺栓底部的摩擦系数区间。根据螺栓在拧紧过程中的机械平衡关系，可以得到螺纹反作用扭矩来计算螺纹与支承面的摩擦系数。考虑三种情况，即无润滑剂、螺纹和螺母表面润滑。通过重复实验进行统计分析，以研究夹紧力对摩擦系数变化行为的影响。在没有润滑的情况下，反复拧紧会导致摩擦系数增加，从而导致夹紧力降低。使用润滑剂时，可以保护接触面，反复拧紧时获得的夹紧力更加稳定。实验结果表明，该方法可用于研究反复拧紧过程中摩擦系数的变化行为。即不加润滑剂，螺纹和螺母表面润滑。通过重复实验进行统计分析，以研究夹紧力对摩擦系数变化行为的影响。在没有润滑的情况下，反复拧紧会导致摩擦系数增加，从而导致夹紧力降低。使用润滑剂时，可以保护接触面，反复拧紧时获得的夹紧力更加稳定。实验结果表明，该方法可用于研究反复拧紧过程中摩擦系数的变化行为。即不加润滑剂，螺纹和螺母表面润滑。通过重复实验进行统计分析，以研究夹紧力对摩擦系数变化行为的影响。在没有润滑的情况下，反复拧紧会导致摩擦系数增加，从而导致夹紧力降低。使用润滑剂时，可以保护接触面，反复拧紧时获得的夹紧力更加稳定。实验结果表明，该方法可用于研究反复拧紧过程中摩擦系数的变化行为。在没有润滑的情况下，反复拧紧会导致摩擦系数增加，从而导致夹紧力降低。使用润滑剂时，可以保护接触面，反复拧紧时获得的夹紧力更加稳定。实验结果表明，该方法可用于研究反复拧紧过程中摩擦系数的变化行为。在没有润滑的情况下，反复拧紧会导致摩擦系数增加，从而导致夹紧力降低。使用润滑剂时，可以保护接触面，反复拧紧时获得的夹紧力更加稳定。实验结果表明，该方法可用于研究反复拧紧过程中摩擦系数的变化行为。