Design and multiscale optimization of automotive CFRP B-pillar inner plate layups by design and molding process

To enhance the lightweight level, crash safety, and production efficiency of automotive B-pillars, this paper proposes a structure-process collaborative design scheme for the integrated inner panel of carbon fiber reinforced polymer (CFRP) B-pillars, which replaces high-strength steel based on the “part integration” concept. Considering the constraints of layup and molding processes, a multi-level design (layup block, shape, and number of layers) and multi-scale optimization (layup angle and thickness) are conducted for the CFRP inner panel. The design optimization results show that the stiffness of the CFRP B-pillar inner panel under key working conditions such as three-point bending and compression is significantly higher than that of the original high-strength steel component. Meanwhile, a surrogate model combined with the improved particle swarm optimization–bacterial foraging optimization (PSO–BFO) algorithm is further adopted for multi-objective optimization. After optimization, the three-point bending stiffness and first-order bending mode of the CFRP B-pillar inner panel are increased by 43.9% and 121.1%, respectively, compared with the original scheme, while achieving a remarkable 70% weight reduction. Based on the optimized design, the proposed CFRP B-pillar inner panel is manufactured using an resin transfer molding (RTM, closed-mold molding) device. Three-point bending and modal tests are carried out on the fabricated CFRP B-pillar inner panel, and the comparative verification between simulation and test results shows an error of <10%. Finally, the CFRP B-pillar inner panel is integrated into the high-strength steel B-pillar assembly for drop weight impact testing, with a displacement error of only 7.65% between the test and simulation results. This effectively verifies the excellent energy absorption characteristics of the design and the accuracy of the simulation model. This study successfully achieves significant improvements in B-pillar stiffness and dynamic performance as well as substantial lightweighting, providing an important reference for the high-performance and lightweight design of automotive B-pillars.