Official Answer
Answer
'Oil canning' or 'snap-through' is a form of elastic instability that occurs in single-turn wave springs when the ratio of the wave height $h$ to the material thickness $t$ is too high. If the spring is compressed, it may reach a point where it 'snaps' into an inverted shape or a flattened state with a sudden drop in load. This is mathematically similar to the buckling of a shallow arch. To avoid this, designers should keep the $h/t$ ratio within a range where the spring rate remains positive. If the rate $dk/df$ becomes negative, the spring is unstable. This is a critical failure mode in switch mechanisms where a positive tactile 'click' is required, but it is a failure in structural preload applications.
