Structural Optimization of a Pickup Frame Combining Thickness, Shape and Feature Parameters for Lightweighting

The methods for improving the torsion stiffness of a pickup chassis frame were discussed, including increasing the part thickness on frame, enlarging the cross section of rails, and adding bulkhead feature inside the rails. Sizing optimization was conducted to get the optimal thickness configuration for frame parts and meet the siffness requirement. The cross section of frame rails was parameterized and shape optimization was conduted to get the optimal rail cross sections for stiffness improvement. Additional bulkheads were added to the frame rails, and sizing optimization conducted to find the most effective bulkheads to add and their optimal gauge. A material efficiency ratio mu is used to evaluate the efficiency of a design change with respect to torsion stiffness. Among those torsion improvement methods, adding bulkhead feature gives the highest material efficiency ratio, but the stiffness improvement is very limited. Enlarging the rail sections and increasing the part thickness can improve the torsion to over 9% while the material efficiency ratio is relatively low. Simultaneous structural optimization was conducted combining above two and all torsion improvement methods to obtain the most efficient lightweighting design. For different design targets, the corresponding method combination was obtained through optimization. For torsion improvement within 3.2%, adding bulkhead feature is the most efficient design with high material efficiency ratio (mu > 7.936 kN-m/rad/kg). For improvement target 3.2%-5.4%, the design combining adding bulkheads and enlarging the rail sections is most efficient with mu in range of 3.861-7.936 kN-m/rad/kg. For improvement target 5.4%-10.3%, the design combining all three improvement methods gives the optimal performance, with material efficiency ratio mu in range of 2.333-3.861 kN-m/rad/kg. For target over 10.3%, above stiffness improvement methods do not offer an efficient solution and the frame needs to be redesigned. This study gives guideline on adopting the methods for stiffness improvement and achieving the optimal lightweigting design.