Understanding stiffness degradation of composite helical springs with multi-braided layers under impact

Understanding stiffness degradation and developing suitable damage detection method for composite helical springs (CHSs) are important for their application and further development. In this study, a coupled plasticity-damage model for capturing stiffness degradation of CHSs with multi-braided layers (MBLs-CHS) is developed. Experimental results show that there is minor damage that only happens in the resin component of MBLs-CHS during impact. The element removal fraction in the simulation result is used to evaluate the damage severity, which is suggested to increase with impact energy (E_i) and decrease sequentially for CHSs with single, double, and triple braided layers (i.e., SCHS, DCHS, and TCHS). Specifically, damage severity of TCHS decreases by 51.3 % under 60 J impaction compared to that of SCHS. Finally, the time domain analysis method is introduced to monitor damage in real time. The amplitude intensity profiles under various Ei of CHSs have been fitted to predict the global stiffness degradation of CHSs in real time.