Optimum Design of Glass and Carbon Fiber Reinforced Polymer Leaf Springs

Background: Fibre-reinforced polymer composites offer opportunities to reduce the mass of automotive suspension components while maintaining specified structural performance. However, optimum leaf-spring design requires simultaneous consideration of material properties, geometric parameters and mechanical constraints. Objective: This study aimed to minimise the mass of laminated semi-elliptic leaf springs manufactured from glass fibre-reinforced polyester (GRP) and carbon fibre-reinforced polyester (CRP), with conventional carbon steel used for comparison. Methods: A constrained nonlinear optimisation problem was formulated using the number of leaves, normalised leaf width and thickness, fibre volume fraction and fibre orientation angle as design variables. The constraints included strength, deflection, geometry and natural frequency. A load of 1000 N, an eye-to-eye length of 1100 mm and a maximum permitted deflection of 150 mm were adopted. The optimisation was performed using MATLAB, and the resulting solutions were assessed against the Lagrange and Karush–Kuhn–Tucker optimality conditions. Results: The reported optimum designs comprised four leaves with a thickness of 5.5 mm. The GRP spring had a width of 35 mm and a mass of 1.8 kg, while the tabulated CRP design had a width of 33 mm and a mass of 1.3 kg. Both composite designs had a fibre volume fraction of 0.65 and a fibre orientation angle of 0°. Relative to the 8.3 kg steel spring, the calculated mass reductions were approximately 78% and 84%, respectively. Conclusion: Under the adopted assumptions and constraints, both composite materials demonstrated substantial potential for leaf-spring mass reduction.