Quote:
Originally Posted by Kidkraz
The ... holes prevent the crack from growing longer.
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If you visualize it in your mind, the stresses concentrate at the tiny bit of material at the very narrow end of the crack. These concentrated stresses cause the crack to propagate further. By drilling a hole, you open up that very narrow region - the stresses are not eliminated, but they are distributed.
Think of putting the blade of a table knife down between your fingers, edge first, pressing into the flesh. You don't need a lot of force for the edge to cut into your skin. Now think of turning the knife so the flat is pushing into the skin. You can apply the same amount of force as before, but because the force is distributed over a wider area, you don't get cut.
Bill