Glass fibre reinforced epoxy leaf spring design
by W.G. Gottenberg, K.H. Lo
International Journal of Vehicle Design (IJVD), Vol. 4, No. 3, 1983

Abstract: Composite leaf springs constructed of unidirectional glass fibres in an epoxy resin matrix are being recognized as a viable replacement for steel springs in truck and automotive suspension applications. Because of the material's high specific strain energy storage capability compared with steel, direct replacement of multi-leaf steel springs by mono-leaf composite springs is justifiable on a weight saving basis. Further advantages of composite springs accrue from the ability to design and fabricate a spring leaf having continuously variable width and/or thickness along its length. Such design features will lead to new suspension arrangements in which the composite leaf spring will serve multiple functions thereby providing part consolidation and simplification of the suspension system. This paper reviews the function of a spring as an energy storage device. It examines in detail the influence on that function of the material of construction (unidirectional glass fibres in epoxy versus steel) and of spring geometry. The design latitudes afforded by the variable thickness/width options are illustrated. Finally, the significance of shear stress components in planes containing the fibres is examined, particularly in its relation to the selection of the thermoset resin matrix. Complete knowledge of shear stresses is not important in a steel part undergoing flexure, while, with such a reinforced resin part, shear stresses rather than normal stress components may control the design. Procedures are presented for evaluation of design stresses due to simple flexure as well as such secondary loads as axle windup.

Online publication date: Sun, 25-May-2014

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