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Unread 07-01-2008, 06:10 PM   #40
MayDay
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Talking Hole at the End of a Crack Reduces Crack Propagation

Swamprb and TysDad, you are both correct that drilling a hole at the end of the crack will help stop the crack from growing. The trick is to make sure that the hole is drilled AT the end of the crack!

Essentially, the stress at the end of the crack is inversely proportional to the radius of the end of the crack. By drilling a hole at the end of the crack, you increase the radius, which effectively reduces the stress on the crack, so that it will have less chance to grow (Griffith's Theory, Unstable Crack Growth, 1920).

For example, in the early 1950's, a lot of de Havilland aircraft were falling out of the sky. The planes split in half in midair from stress cracks that started at the corners of the square windows that were in use at the time.

For the mathematically inclined, this is all explained here: Stress Concentrations & Griffith Crack Theory, where "a" is related to your crack geometry.

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