Fatigue strength of S-Ply® leaf springs





S-Ply® is a glass-fibre composite material that is suitable for the highest dynamic requirements. The load carrying and supporting material is a strictly parallel-orientated, non-woven, glass- or carbon-fibre laminate (UD-prepregnated).  


The glass-fibres are not stretched and not bent. In contrast to metallic materials with an isotropic structure, they are direction dependent and therefore can be aligned to suit the material structure. Epoxy resin compounds are used as binding agents. Their special balanced composition ensures high adhesive to the glass fibre surface, resulting in optimum dynamic and electrical properties. The ratio of matrix resin and reinforcement fibres has been chosen to profit from all the benefits offered by the raw materials selected to form the composite material. 

The matrix fulfils a number of important tasks. It provides fixing for the fibre in the desired arrangement and supports it against buckling when under compressive stress. In addition, it has good load carrying and transmission properties, thus it directs the forces applied into the fibres. Hence, the polymer matrix has a decisive effect on the toughness and the tolerance to damage of the composite materials. 


Important features of the high performance composite material


S-Ply® leaf springs are designed to have a high elastic energy retention capacity (low modulus or elasticity), combined with a high mechanical strength.


Result: In comparison to steel leaf springs, S-Ply® leaf springs have significantly greater spring action, superior internal damping and a substantially greater  ability to store elastic energy compared with spring steel.


The individual prepregnated glass-fibre layers from S-Ply® leaf springs of can be oriented at precalculated angles to each other.


Result: All available mechanical strength is focused exactly where it it needed. For springs: ideal adaption of the leaf spring geometry and the material to suit the load.


S-Ply® leaf springs provide a balanced ratio of mechanical strength to weight, high fatigue strength, corrosion resistance, impact resistance and electrical insulation.

Result: These characteristics make it possible to construct high performance, mechanical and dynamic systems.



The stress-cycle diagram indicates the fatigue strength of a 4mm thick S-Ply® leaf spring under tension-compression fatigue load.