Static Mechanical Performance of Composite Elliptic Springs

Composite elliptic spring is a new concept as an application of fiber reinforced plastics in automotive suspensions. It functions in the same vertical deflection mode and packaging space as a steel coil spring and has the potential of saving as much as 50 percent by weight over a steel spring. The unique feature of the elliptic spring is that the fibers are utilized in tension instead of shear, thus avoiding the inherent weakness of a composite material in a coiled configuration. Several elliptic spring elements can be mounted in series to obtain the desired spring rate. In this paper, mechanical performance and failure analysis of composite elliptic springs under static loads are presented. Both thick and thin walled elliptic spring elements constructed from unidirectional E-glass fiber reinforced epoxy tapes were tested in static compression. Interlaminar shear failure is the primary failure mode in these springs. Both failure load and spring rate depend on the thickness of the spring. Joining of spring elements by bolts is also investigated.