Official Answer
Answer
Fretting corrosion occurs at the contact points (crests and valleys) between the wave spring and the mating surfaces or between turns in a multi-turn spring. Vibration causes micro-oscillations, breaking down the protective oxide layer of the metal (e.g., $Cr_2O_3$ on stainless steel). The resulting fine debris acts as an abrasive, creating pits that serve as stress concentrators $K_t$. Failure analysis often shows 'cocoa' (reddish-brown powder) for carbon steel or black oxide for stainless. Using dry film lubricants (like $MoS_2$) or increasing the preload to prevent relative motion are effective countermeasures.
