Investigation of composite leaf spring in the early 60’s failed to yield the production facility because of inconsistent fatigue performance and absence of strong need for mass reduction. Researches in the area of automobile components have been receiving considerable attention now. Particularly the automobile manufacturers and parts makers have been attempting to reduce the weight of the vehicles in recent years. Emphasis of vehicles weight reduction in 1978 justified taking a new look at composite springs. Studies are made to demonstrate viability and potential of FRP in automotive structural application. The development of a liteflex suspension leaf spring is first achieved. Based on consideration of chipping resistance base part resistance and fatigue resistance, a carbon glass fiber hybrid laminated spring is constructed. A general discussion on analysis and design of constant width, variable thickness, composite leaf spring is presented. The fundamental characteristics of the double tapered FRP beam are evaluated for leaf spring application.
In a FRP leaf spring , the inter laminar shear strengths is controlled by the matrix system used . Since these are reinforcement fibers in the thickness direction , fiber do not influence inter laminar shear strength. Therefore, the matrix system should have good inter laminar shear strength characteristics compatibility to the selected reinforcement fiber. Many thermo set resins such as polyester, vinyl ester, azpoxy resin are being used for fiber reinforcement plastics(FRP) fabrication . Among these resin systems, epoxies show better inter laminar shear strength and good mechanical properties. Hence, epoxide is found to be the best resins that would suit this application. different grades of epoxy resins and hardener combinations are classifieds , based on the mechanical properties.
Among these grades , the grade of epoxy resin selected is Dobeckot 520 F and the grade of hardener used for this application is 758. Dobeckot 520 F is a solvent less epoxy resin which in combination with hardener 758 cures into hard resin . Hardener 758 is a low viscosity polyamine . Dobeckot 520 F , hardener 758 combination is characterized by
Good mechanical and electrical properties.
Faster curing at room temperature.
Good chemical resistance properties
The leaf spring behaves like a simply supported beam and the flexural analysis is done considering it as a simply supported beam. The simply supported beam is subjected to both bending stress and transverse shear stress. Flexural rigidity is an important parameter in the leaf spring design and test out to increase from two ends to the center.
CONSTANT THICKNESS, VARYING WIDTH DESIGN
In this design the thickness is kept constant over the entire length of the leaf spring while the width varies from a minimum at the two ends to a maximum at the center.
CONSTANT WIDTH, VARYING THICKNESS DESIGN
In this design the width is kept constant over the entire length of the leaf spring while the thickness varies from a minimum at the two ends to a maximum at the center.
CONSTANT CROSS-SELECTION DESIGN
In this design both thickness and width are varied through out the leaf spring such that the cross-section area remains constant along the length of the leaf spring.
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