A LOAD RETENTION MODEL AND FAILURE CRITERION FOR BOLT LOOSENESS TO IMPROVE JOINT RELIABILITY IN AUTOMOTIVE APPLICATIONS

摘要

Initially tightened bolts can loosen when subjected to cyclic loads. The loosen bolts may not only make the vehicle noisy, but also cause a severe vehicle degradation and reduce its service life. Studies show that many engineering problems are caused by loosening bolts at the joints. Bolt looseness is a complicated problem affected by many factors. In this paper, experimental studies were conducted on the bolt looseness behavior of a side mounted stabilizer bar attachment joint. From the results of the experiments, we have concluded that initial clamping force, bolt size, surface finish, and back retention plate were the four most significant variables affecting the bolt looseness. By controlling these factors and optimizing the mounting configuration, the joint integrity problems caused by bolt looseness could be greatly improved. It was also found that the relation of the clamping force versus the number of load cycles could be described by a logarithmic relationship. Based on this relationship, we developed a load retention model for the stabilizer bar attachment that could calculate the remaining clamping force of a bolt joint at any number of cycles of load applications. Furthermore, with the slope of the equation and the initial clamping conditions, it is possible to predict whether a bolt is going to loosen. Thus provide a useful tool for improving the reliability of the bolt joint design.