关键词: 复合材料；螺栓连接；力矩衰减；蠕变效应；拧紧策略；分步拧紧

Abstract: Due to their advantages such as low density, high strength, corrosion resistance and flexible design, composite materials are increasingly widely used in the manufacturing of automotive parts, which helps to achieve vehicle lightweight and meet diverse appearance and functional requirements. However, it has been found in practical applications that when composite materials are connected by bolts, the torque decay varies due to the different material strengths, posing a challenge to the reliability of threaded connections. This paper focuses on bolted connections of composite materials in automotive assembly, targeting the issue of torque attenuation during the tightening process. It systematically analyzes the influence mechanisms of factors such as material properties, creep effects, and tightening strategies. Based on the single-factor experimental design, the experimental results show that in the connection of composite materials, when the tool speed is reduced from 500 r/min to 10 r/min and distributed tightening is adopted, the residual torque value increases by 33.6%. Furthermore, when retightening is performed after a 5 h interval, the residual torque value increased by an additional 23.2%. Therefore, the strategies of reducing the tool speed, adopting stepwise tightening, and implementing retightening after an interval of more than 5 h prove effective in suppressing torque decay, providing a feasible technical direction for related process optimization.

Key words: composite materials; bolted connections; torque decay; effect of creep; tightening strategy; staged tightening