Analysis and determination of bolt tightening process factors for composite structures under multiple working conditions

Abstract

When developing the tightening process for composite bolts, ensuring that the target preload( F) required by design is achieved is a key scientific issue in meeting the mechanical properties of the connected structure. Variations in complex process factors during tightening have a large effect on the tightening torque( T)-preload curve( F), and the mechanism by which the tightening process factor affects the target preload must be considered. Using experimental means, the significance and coupling effects of tightening speed, lubrication conditions, tightening areas, joint sealants and washers have been systematically investigated. The tightening torque( T), torque coefficient( K), preload( F) and the peak stress coefficients X( σ) and interlaminar stress coefficients Y( σ) within the composite laminate are used as the main response variables, and a mathematical model between each response variable and the process factor is established to analyse the effect of significant factors on the response variables from a quantitative perspective. Finally, with a certain size of preload( F) as the optimisation target, the optimisation analysis of the tightening speed is carried out for four working conditions with different sealing conditions and different tightening area, and the optimum tightening speed for each working condition is determined. Based on the above study, an analytical method was proposed to determine the reasonable interval of tightening process parameters in this paper.