Effect of tightening process parameters on the T-F curve of bolts in composite structures

Abstract

Aircraft composite structures are widely joined using bolts. Differences in the tightening process parameters for tightening bolts can significantly affect the tightening torque (T)-preload (F) relationship. Some of the more significant process parameters include lubrication conditions, tightening speed, tightening area, sealant and washer. The experimental study compared the differences in T-F curves, friction coefficients, torque coefficients and yield preload during the tightening process for different values of the process parameters. The focus was on the state of the thread surface, the state of the bearing surface, the diffusion of the lubricating medium and sealant with preload, etc. The distribution of the T-F curve was obtained for all possible values of the process parameters. As the tightening speed increases, both the inter-thread friction coefficient and the macroscopic increase in the coefficient of friction on the bearing surface are observed when tightening the bolt head. The presence of sealant reduces the inter-thread friction coefficient. The size of the T-F curve area reflects the sensitivity of the bolt tightening process to the various process parameters. The size of the T-F curve area reflects the sensitivity of the bolt tightening process to the various process parameters.