A Material Efficiency Ratio to Evaluate the Methods for Improving the Torsional Rigidity of a Pickup Chassis Frame

While offering improved crash worthiness and significant lightweighting opportunities, the increased use of advanced high strength steels (AHSS) may compromise the stiffness and NVH performance of vehicles due to reduced part thickness. Different methods to improve the torsional rigidity were studied on a pickup chassis frame. These methods include adding bulkhead pairs as reinforcement, increasing the thicknes of frame parts, and enlarging the closed sections on the rails. Structural optimization was conducted for each stiffness improvement method and the minimal mass increase required to reach the improvement targets was obtained. A material efficiency ratio μ is proposed in this research and used as a criterion to evaluate the efficiency of a mass increase to improve the structural stiffness and NVH characteristics of vehicles. Based on this parameter, the methods to improve the torsional rigidity of the pickup frame in all design spaces were evaluated. The adding bulkhead pair option offers the highest material efficiency ratio, but the potential for improving the torsional rigidity is limited. Conversely, increasing the part thickness and enlarging the closed sections on rails give higher torsion improvement potential, while the material efficiency ratio is much lower.

Structural optimization combining adding bulkhead pairs and enlarging the rail sections was conducted to fully utilize the advantages of both rigidity improvement methods. And the results show higher material efficiency and more potential for rigidity improvement than each individual method. This material efficiency ratio proposed is valuable in vehicle development to evaluate the efficiency of a design change for lightweighting.