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Correlating Dynamic & Static Results

Correlating Dynamic & Static Results

Correlating Dynamic & Static Results

(OP)
Hi,

I have a structure which is dynamically loaded in tension.  The structure basically consists of 3 in-line steel straps bolted to each other and to rigid locations at the end:
- - -



A dynamic load is applied as a Force/Time curve.  The results are reviewed for failure by looking for stresses beyond UTS or strains beyond maximum elongation of the steel.  None of the components exhibit any "complete" failure, ie one strap/piece completely detaching from another.



When I calculate the various load cases by hand, using static assumptions, the structure is predicted to fail by any number of modes - tear-out, bearing/crushing stress, failure through the section.



Is there a "rule of thumb" that can be applied to my static calculations to bring the results more in sync with the dynamic results - some kind of "dynamic load factor" that can be applied?



Thanks,

Jeff

RE: Correlating Dynamic & Static Results

None of which I'm aware. There probably are "rules of thumb" out there for this type of thing, but they would have to be very problem-specific. Give me a generic rule-of-thumb for something like this, and I'm sure I can quickly give you a reasonable case which is a gross exception.

I'm puzzled by a statement of yours--you said you did static calculations "by hand, using static assumptions". Why aren't you running a static FEA analysis also? Not knowing your specific problem, it may be completely reasonable to do hand analyses. However, I would first make sure that your "static closed form solution" is consistent with a "static fea solution".

 I mean this: there are two sources of "error" (term used loosely here) between your dynamic FEA solution and your static closed-form solution:

dynamic vs. static and FEA vs. "theory" (again, loose use of terms).  

You are focusing on the first, which is almost certainly significant at some level. However, there may be a significance to the second that overwhelms the first. You should first rule this out before you start chasing down the other.
Just thoughts . . .

Note that there may be other issues going on completely apart from this. As you didn't list many details of assumptions, I didn't want to speculate as to what other assumptions (material models, various nonlinearities) could be affecting things.
Good luck.
Brad

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