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Mechanical defection
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Posted by: pollano

02/04/2005, 11:54:57

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I have an aluminmum box (not a casting) .090" thk by 8.5"widex5.5"deepx1.5" high. It is sealed at sea level. What is the deflection on each face at 35,000 feet. Can anyone help me out with this.

Thanks
Norm P.







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Re: Mechanical defection
Re: Mechanical defection -- pollano Post Reply Top of thread Forum
Posted by: Cragyon
Bart
02/05/2005, 10:03:53

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I think the first question is, does the box realy need to be sealed a sea level? Is it sealed by process, or are you assuming the box is sealed by design requirements? If the box contains a unique environment, such as a noble gas or is suseptable to atmospheric changes then sealing maybe a requirement. I have designed electronic enclosures for years for military, commercial and space applications, and often the boxes have orings / elastomers and have small vent holes (.031") drilled within the enclosure. The vent holes are for equalizing the external / internal pressure. They are small enough to prevent moisture accumulation within the enclosure (so physics experts say). Aviation electronics are normally conformal coated to provide additional protection from the environment. There is a simple calculation one can do to determine the rate of pressure equalization due to alitude changes.

Now, to determine the pressure difference all you have to do is assume 14.7 psi at sea level minus the atmospheric pressure at the desired altitude. say 4 psi (check this I'm guessing), and your pressure is 14.7-4 = 10.7 psi internal pressure. As far as stresses on the box this pressure would be equally disposed about the internal geometry. Calculating the stress, say on a bolted on cover, just determine the effective area the internal pressure is acting on and you have it. Normally, a FEA model is created to very structural conformance.

Good luck







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Re: Mechanical defection
Re: Mechanical defection -- pollano Post Reply Top of thread Forum
Posted by: randykimball
Barney
02/04/2005, 18:55:10

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Is this a test question?



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