#721: Wearometer

It’s still surprising to me that bubbles can actually do damage to hardened surfaces, by their sudden collapse: a process known as cavitation. I’ve been thinking about ways to use bubbles as an indicator of surface characteristics.

When an object is submerged in liquid and is heated, bubbles will form and grow at microscopic nucleation sites on its surface. In general, the more sites there are, the more bubbles form. Today’s invention exploits this to provide a measure of surface damage.

As a component undergoes wear, the number of nucleation sites will increase. Smallish engineered items, from a doorkey to a drillbit, would be gripped by a pair of copper jaws at a precisely determined location and submerged in a small bath of low boiling-point liquid (eg a domestic refrigerant).

The jaws would then be heated in a controlled way, so the volume of vapour formed from the bubble generation, over a fixed period, can be measured (before condensing the vapour for the next session). This process causes no additional damage, of course, to the material (and might even clean it).

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