Answer
When a wave spring is compressed, the circumferential length of the wire remains nearly constant, causing the mean diameter $D_m$ to expand. For a spring in a bore, this expansion is constrained. The expansion $\Delta D$ can be approximated by $\Delta D = 0.02 \cdot \frac{w^2 - f^2}{D_m}$, where $w$ is the wave height and $f$ is the deflection. If the clearance between the spring OD and the bore is insufficient, friction between the spring and the bore wall creates a hysteresis loop in the load-deflection curve. This 'binding' increases the apparent stiffness and can lead to localized stress concentrations $\sigma_{total} = \sigma_{bending} + \sigma_{friction}$. Engineers must ensure the OD at work height $OD_{work} = OD_{free} + \text{expansion}$ is less than $D_{bore}$ to maintain predicted load accuracy.
