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At 02:43 PM 6/22/2005, you wrote:
The error in reasoning here (7075 is twice as strong as 6061 so it can be half as thick) is that the bending strength of a plate is far more influenced by its thickness than by material strength. This is in addition to the fit problems pointed out by Dean.
Just not a good idea.
True. Deflection varies with the reciprocal of the cube of the thickness. A plate half as thick deflects 8 times as much under the same load. Thus, you can't simply reduce the plate thickness.
However, you could use a 1/2 inch thick 7075 plate and then machine away low-stress portions, leaving stiffening ribs in just the right places. With this approach, you could cut the weight of the plain 6061 plate about in half, maybe more.
Wouldn't want to do it without the FEA, (including vibration modes) of course.
Bill Dube'
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