Influence of strength grade and surface finish on threaded fastener for reliability application.

The aim of this study is to provide a reliability design methodology based on experience data and theory analyses to choose bolts in terms of strength grade and surface process, therefore, to ensure safe car operation The components under investigation are some clamped joints made of aluminum alloy and used in micro car chassis to connect the lower arm to the body. The aluminum alloy is realized by three kinds of surface process: dacro, Ep.FeZn8.C2C, Ep.FeZn8.C2D and three kinds of strength grade: 8.8, 10.9, and 12.9. Some experiences have been appropriately designed with the same process of the actual components on the advanced tightening device. The mean values and standard deviations of bolt yield stress can be obtained via tightening experience whereas the mean values and standard deviations of total tensile stress can be calculated according to bolt load evaluated by means of FEM. Based on stress-strength interference theory the reliability of bolt with different strength grades and surface processes can be calculated, which is useful to choose bolts. Compared the traditional safety factor method, the reliability design method takes into account random factors influence to the preload such as the bolt manufacturing error and the dispersion of the torque coefficient, so it is a more rational approach to select fasteners and has important engineering significance to the threaded connection safe operation for the automotive industry. [ABSTRACT FROM AUTHOR]