Effect of bolt tightening torque on fatigue life of multi-bolted composite structure

螺栓拧紧力矩对复合材料多钉连接结构疲劳寿命的影响

¹ School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China
² Institute of Aircraft Composite Structures, Northwestern Polytechnical University, Xi'an 710072, China
³ Aerospace Research Institute of Materials and Processing Technology, China Academy of Launch Vehicle Technology, Beijing 100076, China

Received: 28 July 2022

Abstract

Bolt tightening torque has an influence on the fatigue life of the multi-bolted joints which cannot be ignored, but there are few methods to predict the fatigue life of the multi-bolted composite structure by considering the bolt tightening torque. A fatigue life prediction method of the multi-bolted composite structure by considering the bolt tightening torque is proposed. It can take into account the various damages of bolts and laminates and accurately calculate fatigue life and damage evolution of multi-bolted composite structure. The multi-bolted composite structure being composed of T300/BMP-316 composite laminates and TC4 titanium alloy bolts is used to verify the present method. The logarithmic error between the predicted fatigue life and the experimental is 4.36%, and the failure mode is consistent with the experimental. Through the present method, the influence of the bolt tightening torque is explored, in which it is found that with the increasing of bolt tightening torque, the fatigue life increases firstly and decreases, and there is an optimal tightening torque. By observing the damage evolution diagram, it is found that when the tightening torque is below the optimal tightening torque, the damage propagation cannot be effectively restrained, which will lead to the reduction of fatigue life. On the contrary, when the tightening torque is more than the optimal tightening torque, it will cause the initial damage to the test piece, which will also lead to the reduction of fatigue life. In engineering, to choose the best tightening torque of the structure for assembly can effectively improve the fatigue life of the structure.

摘要

螺栓拧紧力矩对多钉连接结构疲劳寿命的影响不可忽视, 但考虑螺栓拧紧力矩的复合材料多钉连接结构疲劳寿命预测方法却很少, 提出一种复合材料多钉连接结构疲劳寿命预测方法, 综合考虑螺栓与层合板的各种损伤情况, 可以准确预测复合材料多钉连接结构的疲劳寿命以及损伤演化情况。采用T300/BMP-316复合材料层合板与TC4钛合金螺栓组成的复合材料多钉连接结构对所提方法进行了验证, 疲劳寿命预测结果与试验值对数误差为4.36%, 且破坏模式与试验结果吻合。通过对螺栓拧紧力矩的影响规律进行探究, 发现随着螺栓拧紧力矩的增加, 疲劳寿命先增加后减小, 存在最佳拧紧力矩。从损伤演化云图中发现当拧紧力矩小于最佳拧紧力矩时, 损伤扩展不能得到有效抑制, 会导致疲劳寿命降低; 反之当拧紧力矩大于最佳拧紧力矩时, 试验件会形成初始损伤, 导致疲劳寿命降低。在工程应用中, 选择结构的最佳拧紧力矩进行装配, 可以有效提高结构疲劳寿命。