Behaviour of FRP-sandwich structures for lightweight composite springs in static and cyclic torsional load cases

Fiber-reinforced polymers (FRP) are established as high-tech materials for special purposes
such as racing cars, planes or bicycles. Nowadays, they are increasingly used for functional parts and machine elements. For lightweight optimization, FRP sandwich structures can be used, which also appear to be suitable for spring applications. But material data availability is often limited for UD-specimen or specific load cases, which makes it difficult to use FRPs for technical springs. In order to reduce this gap and to facilitate the development of new applications, this paper deals with the basic static and cyclic behavior of FRP sandwich strips under torsional load. Therefore, manufacturing methods have been developed, to produce FRP strip specimens with GFRP and CFRP shells containing various core materials. An analytical model was used to describe the static behavior, which shows decent agreement with test results. Initial studies on fatigue characteristics of these strips were carried out as well as tests on associated volute springs. The results contribute to composite lightweight spring design and could extend the range of applications for composite springs in the future.