Interpreting FEM results
Interpreting FEM results
(OP)
Hello all, I have been reading up on the difference between max principal stress and von mises stress. Those principles are easy to understand but I can't seems to make sense of it for a forged material.
I am using DEFORM to simulate the cold forging of a workpiece and the result shows that both the max principal stress and vM stresses are way above the material's UTS and yield strength.
Am I right to say that for a forged material, its stresses should be above the yield strength since it have to plastically deform but below its UTS?
*The said workpiece is already under production. It hasn't crack and looks fine.
I am using DEFORM to simulate the cold forging of a workpiece and the result shows that both the max principal stress and vM stresses are way above the material's UTS and yield strength.
Am I right to say that for a forged material, its stresses should be above the yield strength since it have to plastically deform but below its UTS?
*The said workpiece is already under production. It hasn't crack and looks fine.





RE: Interpreting FEM results
RE: Interpreting FEM results
RE: Interpreting FEM results
forging causes permanent deformation so, sorry, of course cold forging stresses exceed allowables,'cause the material deforms and flows.
another day in paradise, or is paradise one day closer ?
RE: Interpreting FEM results
So your stresses will be way above UTS as you are not using a fully defined stress strain curve. Same here, not sure what DEFORM solution is, is it able to account for the nonlinear material stress strain curve? If yes, there is no way you can see any stresses (other than numerical noise) well above the defined stress strain curve values because you are dictating to the solver that at this strain level this is the stress level.
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RE: Interpreting FEM results
I have also come across Cockcroft-Latham damage criterion (also used by DEFORM). Is there a general value which my material shouldn't excees? I have seen a paper somewhere stating that a damage value exceeding 1 means crack/tearing will occur, is it true? Some the workpiece cracked when DEFORM shows damage value of 0.8 while other workpieces came out fine even with DEFORM's damage value indicating 1.5.
I have been reading up on the above topics but many textbooks and research papers have been said that critical damage or stress values are obtained emperically and trial and error. I was wondering if there are any theorical guidelines that I can follow.
RE: Interpreting FEM results
1) the stresses that occur during the forging, or
2) the residual stresses, after forging ?
during forging, I'd expect that the stresses would be above yield. It makes sense that there's some criteria that'd measure whether the forging process will produce 1 part or 2 (or many). But I've no idea how "they'd" model the metal flow, etc ...
another day in paradise, or is paradise one day closer ?
RE: Interpreting FEM results
There, if the FI > 1.0, failure is predicted.
So this one sounds similar for forging pieces. And my guess is that may be there are internal algorithms inside 'DEFORM' that indicate the failure value depending on the shape, material and final product form etc.
Your best bet is to read up as much as you can on what DEFORM is doing in the background or contact their tech support for references. It seems not many people here are familiar with DEFORM.
www.stressebook.com
Stressing Stresslessly!