Design and analysis of mono composite leaf spring for light weight vehicle

Abstract

This thesis focuses on the replacement of steel or conventional leaf spring of a suspension system with composite material. Design and analysis of composite material leaf spring has become essential in showing the comparative results with conventional leaf spring. The Automobile industry has shown the interest for replacement of steel leaf spring with that of glass fiber composite leaf spring, since the composite has high strength to weight ratio, good corrosion resistance and tailor-able properties. The suspension system in automobile significantly affects the behavior of vehicle, i.e. vibration characteristics including ride comfort, directional stability, etc. leaf spring used in the suspension system of automobile are subjected to millions of varying stress cycles leading to fatigue failure. If the unsprung weight (the weight, which is not supported by the suspension system) is reduced, then the fatigue stress induced in the leaf spring is also reduced. Even a small amount of weight reduction in the leaf spring will lead to improvements in passenger comfort as well as reduction in vehicle cost. In this context, the replacement of steel leaf spring by composite material reduces the weight of leaf springs. In this work, the existing steel leaf (multi-leaf) spring of Huanghai pick up is taken for modeling and analysis. The design constraints are stress and displacement. A composite mono leaf spring of E- glass Epoxy composite material is modeled and subjected to the same load as that of steel leaf spring. Composite mono leaf spring is modeled with constant cross section in CATIA and stress, deflection, modal (natural frequency) safety factor and fatigue analysis of this model is performed using ANSYS 12.0 and results were compared. Analysis results of stress, weight, deflection and fatigue life of existing and mono composite leaf spring is found with a great difference. Mono composite leaf spring has 73.24% lesser stress, 5.3% lesser deflection, 92.9% weight reduction and longer fatigue life than existing leaf spring thereby increased safety factor is observed. Natural frequency of composite leaf is less than existing but which is greater than road frequency (12Hz), so that it is comfortable and resonance is also very much reduced.