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#11
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control failure
Stuart & Kathryn Fields wrote: Don: Be sure to share what you find. I think that I'm only scratching the surface of some stuff. One thing I found and had never seen before was an equation relating the increase in stress due to a crack. It scares the hell out of me. I'm afraid to use a metal fork in my salad. The equation basically says that the max stress is 2 times the load divided by the area times the square root of the crack length divided by the radius of curvature of the end of the crack!!! If the radius of curvature was equal to the crack length, the max stress is already twice what you would calculate using the applied load and the element cross section. Now put a reasonably sharp crack and see what happens....as the radius approaches 0.001 times the length of the crack......???? That is because the load is not equally spread across the part, but is concentrated at the end of the crack. Think about a piece of metal bar in tension with a crack halfway across it. The cross sectional area that has already seperated cannot bear any load at all as it has already failed. The end of the crack is taking a lot of load because the crack pulls apart when it is under tension. Solution: Don't use cracked parts!! (Well duh) Don W. |
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