Composite helical springs with cladding structures - Design, manufacturing, and mechanism studies

Helical springs are indispensable mechanical parts and have been widely used in industrial applications. In this study, five types of composite helical springs were fabricated based on the lost mold method by controlling different fiber contents and reinforcement structures, forming three carbon fiber unidirectional composite helical springs (UCHS) with fiber content of 60%, 65%, and 70% (UCHS 60%, UCHS 65% and UCHS 70%) respectively, and two cladding structure composite helical springs (CCHS) with fiber content of 70% and the core structure made by unidirectional carbon fiber, but the outer layer structure is weft-knitted tube made of aramid fibers and ultra-high molecular weight polyethylene fibers (CCHS-A and CCHS-U) respectively. The static compression test shows that the spring constant increases with the increase of the fiber content. The cladding structure in the composite helical spring can significantly increase the spring constant when the fiber content is the same. Among them, CCHS-A significantly improves the load-bearing capacity and stability of the composite spring. The stress distribution of each spring in the process of static compression was further analyzed by using the finite element method. The simulation results show that if the stress distribution of each coil is the same, the stress distribution of each coil is sinusoidal and the stress in the center of the spring wire is the smallest. The stress distribution of CCHS is more uniform than that of UCHS. Furthermore, a prediction of spring constant as a function of outer layer number of CCHS were conducted based on experimental and simulation results, which was of engineering significance for the application of composite helical springs.