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Re: FOS for von-Mises stress criteria

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On Jan 13, 2006, at 7:04 AM, Arun Sarkar wrote:

can anyone suggest what factor of safety (for structural steel) should be used when the checking criteria is von-Mises stress ?
You're playing with fire. Sounds like you have some FEA results you're trying to apply to something like ASD rules. Von Mises stress _If_ you're considering working stress design and _if_ there are no stabiity issues, and _if_ there are no fatigue issues and _if_ you're talking about primary stress only and if the material is structural steel where the ultimate stress doesn't govern the allowables, the margin against first yield is about 1.6. So keep your von Mises stress to about 60% of the minimum specified yield value. If any of the foregoing ifs aren't met you're out of luck with simple-minded rules of thumb, particularly if you're trying to apply limit analysis procedures. You need to understand what the basis of your particular design code actually is, and match your FEA results to it.

'Factor of safety' is a silly phrase. It's a number that you only need because you don't know what it is.

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com       | this distance"   (last words of Gen.
____________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw


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