Answer
In nested wave springs, multiple layers of flat wire are in direct contact. When the spring is compressed, these layers slide against each other, generating inter-turn friction. This friction manifests as hysteresis in the load-deflection curve, where the load during the compression stroke is higher than the load during the return stroke at the same height. The energy lost is $E_{lost} = \oint P \cdot df$. In high-frequency dynamic systems (e.g., fuel injectors), this friction generates heat and can lead to damping. If not accounted for, the heat can cause localized temperature spikes, leading to early stress relaxation. Lubrication (e.g., PTFE coating or oil immersion) is required to minimize this effect and prevent fretting wear between the nested layers.
