Jesse Powers

Iso Clipping and "Important" Percent Volumes

Discussion created by Jesse Powers on Oct 27, 2016
Latest reply on Oct 27, 2016 by Jesse Powers

Hey, FEA wizards, etc


I've been doing FEA for quite some time-- using iso clippings...  As a rule of thumb, when I do look at Iso Clippings, I generally ignore any stress elements that take up less than 0.02% geometric volume of the model (or less than 0.10% element "volume").  I don't have any technical understanding of this, however, because it's something I took at face value many moons ago.


As you may know, sometimes a sim (simulation) can give you wild (or at least "loose") max stress values, but only in VERY few elements.  And as you move downward on the iso value ever so slightly, the stress drops dramatically***.


Topic 1)  Do you have any general rules (or even specific rules with specific examples) when analyzing an Iso Clipping?  Even ones that don't refer to "Important" Percent Volumes?


Topic 2)  Do you prefer Standard or Curvature-Based Meshes when dealing with Iso Clippings?  I generally use Curvature-Based meshes when dealing with Iso Clippings, but not always.


Topic 3)  As you understand it, should you look at the failure mode of a part (based on the inherent initial crack size associated with both the material and production method) when you're analyzing Iso Clippings?**



** The way I look at it, the Iso Clipping has to be above the yield strength AND go through the body of the part; the Iso Clipping (above or very close to the yield stress) has to touch both opposing surfaces, or be so close as to cause concern, before a re-design-- or double-checking your sim set-up-- is necessary.


*** I've noticed this: say you have a model that you simplify for FEA, and you use different fixturing and load schemes (with varying degrees of complexity to mimic roughly, at first, the real-life stressing, and then, finally, with greater accuracy).  While the different set-ups may report quite different max stress values (e.g. 48 MPa, for one, and 31 MPa, on the next one), the Iso Clipping values at the same element volume (or geometric volume), will be much closer (e.g. 19 MPa, and 17 MPa, at 0.10% element volume for both).  Those might be exaggerated examples, but I hope it illustrates what I'm curious about discussing.


I looked online for a bit, and couldn't find anything of this sort.  So, I'd like to start the discussion.  Do feel free to post links if you've found anything relevant.