Fatigue life prediction of passenger car wheel bolts under combined loads: Influence of tightening torque and misalignment

Wheel bolts play a critical role in vehicle safety and performance by sustaining vehicle weight, dynamic loads, and road-induced torques, while maintaining sufficient clamp force to prevent slippage at the wheel–hub interface. Traditional fatigue design approaches often treat wheel bolts as purely axially loaded members; however, extensive experimental evidence reveals complex loading conditions that involve significant bending and multi-axial stress states. This study presents a comprehensive analytical-numerical framework for assessing the fatigue life of automotive wheel bolts subjected to combined assembly-induced stresses, geometric misalignments, and external loads. A novel tapered contact pressure model is developed to capture the non-uniform pressure distribution arising from bolt bending and tightening torque. The evolution of contact area, resultant forces, bending moments, and frictional torque is systematically analyzed through iterative contact algorithms. Superposition principles are then applied to combine assembly stresses with service loads to predict the overall stress state. The Gerber, Goodman, and Soderberg fatigue criteria are used to evaluate the fatigue safety factor, taking into account realistic material properties, stress concentrations, and load variations. The model provides practical design recommendations regarding optimal tightening torque, permissible misalignment tolerances, and the effects of bolt number and pitch circle diameter on durability. By quantifying these influences, the study bridges the gap between theoretical bolt design and real-world automotive applications, offering a robust tool for enhancing safety, reliability, and cost-effectiveness.