An analytical model for predicting compressive behaviour of composite helical Structures: Considering geometric nonlinearity effect

Composite helical structures (CHS) can store and release strain energy through elastic deformation, which has a good application prospect in automobile, aerospace and other fields, such as shock-absorbing spring, deployable antenna, etc. Compressive behaviour (i.e. stiffness, strength and load–displacement relationship) is one of the most important basic mechanical properties of CHS. In order to accurately predict the compressive behaviour of CHS, this paper proposes a new analytical model considering geometric nonlinearity effect. In the geometric model, the geometric parameters of CHS change continuously with the increase of compressive load. The load–displacement relationship considering geometric nonlinearity is deduced by accumulative compressive load increment and accumulative compressive deformation increment. The compressive stiffness of CHS is obtained using linear fitting with least square method. On this basis, the analytical expression of compressive strength of CHS is derived. The predicted results are compared with experimental data from literatures. It is shown that predictions using the new analytical model correlated well with experimental results. Considering geometric nonlinearity effect in the analytical model can predict the compressive behaviour of CHS more accurately. The analytical model is used to further analyze influences of helix angle and helix diameter on the compressive behaviour of CHS.