Optimization of the Bolted T-Joint of an Electric Bus Body Frame Considering the Fatigue Performance

This work focuses on the robust optimization of the bolted T-joint part of the steel-aluminum body frame of an electric bus, aiming to improve the performance of fatigue durability of the local structure of the bolted T-joint part. First, finite element model is built for the bolted T-joint part connecting the chassis and the side of the body frame for fatigue durability analysis. Surrogate model for design optimization is fitted by the Kriging method based on the finite element (FE) analysis data. Then, a multi-objective optimization problem is formulated to enhance the fatigue life of the element with the worst fatigue durability performance, and to decrease the deformation of the element with the largest deformation, by choosing the thickness of the beams of the T-joint part as the design variables. A deterministic multi-objective optimization problem is performed by the adaptive simulated annealing (ASA) method. To further improve the reliability of the optimization result, a six-sigma level robust design optimization is carried out based on the Monte Carlo sampling method and the archive-based Micro Genetic Algorithm (AMGA) method. The minimum fatigue times of the optimized bolted T-joint increased by 60.80% compared with that before optimization. The results show that the maximum deformation of the optimized vehicle is reduced by 4.87% and the minimum fatigue times are increased by 25.1% in the common working conditions. The proposed optimization method can effectively improve the comprehensive performance of the bus body frame.