Element size in explicit dynamic analysis with plasticity
Element size in explicit dynamic analysis with plasticity
(OP)
Hi,
are there any guidelines for element size/mesh density when performing impact/crash analysis?
With plastic material behavior, the stresses do not grow infinitely as the mesh density is increased. However, sometimes very fine mesh is needed to obtain converged solution, which results in slow and expensive computation. When the point of interest is for example the maximum plastic strain in the structure, should the element size be decreased over and over again until converged solution is achieved? Or does there exist some standard which says for example that "if the plate thickness is 5mm, then the element size should not be decreased below 2.5x2.5mm"?
-henki
are there any guidelines for element size/mesh density when performing impact/crash analysis?
With plastic material behavior, the stresses do not grow infinitely as the mesh density is increased. However, sometimes very fine mesh is needed to obtain converged solution, which results in slow and expensive computation. When the point of interest is for example the maximum plastic strain in the structure, should the element size be decreased over and over again until converged solution is achieved? Or does there exist some standard which says for example that "if the plate thickness is 5mm, then the element size should not be decreased below 2.5x2.5mm"?
-henki





RE: Element size in explicit dynamic analysis with plasticity
Now the obtained equivalent plastic strain in the integration point of the critical element with different mesh densities was:
- Critical element size 12.5 x 12.5 x 1.25mm, PEEQ = 0.076
- 6 x 6 x 1.25mm, PEEQ = 0.110
- 3 x 3 x 1.25mm, PEEQ = 0.136
- 1.25 x 1.25 x 1.25mm, PEEQ = 0.173
Of course the PEEQ grows when the element size is decreased, as the integration point approaches the sharp corner. But how would I know what is an appropriate size for the element?
I know this is a problem that should have been solved using shell elements, but there are no appropriate shell elements in CalculiX for this kind of problem. The smallest element size I used is way too small in my opinion for this kind of time-consuming analysis, but I don't know what size would be optimal.
I did a search on the subject in this forum, but found little answers. Most topics were concentrated on mesh density of static problems. Could using stress concentration factors to determine the critical stresses in this kind of problem be a valid approach to avoid overly refining the mesh? Or anything else?
-henki
RE: Element size in explicit dynamic analysis with plasticity
I personally feel your results will more rely on your material model at your loading rate. Metal material at high loading rate will be brittle, not ductile any more. These data are often difficult to get.
RE: Element size in explicit dynamic analysis with plasticity
RE: Element size in explicit dynamic analysis with plasticity
By the way, which one do analysts more use as a design guideline: stresses and strains in critical element nodal point or integration point (as the stresses are more accurate in the integration point)? For example when plotting PEEQ against time, should I plot the PEEQ from nodal or integration point?
These things are not fully clear to me, as I don't have anyone to discuss these matters with in my workplace. I'm the only structural engineer in our company and I've just gotten off the school bench :D.
-henki
RE: Element size in explicit dynamic analysis with plasticity