Describe the effect of 'radial wall' ($b$) variation on the stress distribution in a Crest-to-Crest wave spring.

The radial wall $b$ is the width of the flat wire used to coil the spring. In the stress equation $\sigma = (6 \cdot P \cdot D_m) / (n^2 \cdot b \cdot t^2)$, the stress is inversely proportional to $b$. A wider radial wall reduces the bending stress for a given load $P$, thereby increasing the fatigue life. However, a wider $b$ also increases the spring rate $k$ and the total solid height of the spring. Furthermore, if $b$ is too large, the 'radial expansion' during compression becomes more pronounced, increasing the risk of interference with the housing. Designers must balance $b$ to achieve the desired $k$ while keeping stresses within the allowable limits of the Goodman diagram for the selected material.