Learning Forum

[michail.stockfelt]

Hello
I do a lot of nonlinear structural mechanics, where I apply loads until structural failure to find the ultimate load resistance.
I find no features in ANSYS to aid in this. Reasonably there should be so that when the ultimate strain is exceeded - as defined in the Multilinear Isotropic Hardening curve - an element is marked as dead and removed.
Instead I find that when max strain is exceeded, it is the solver that dies. Throwing vague error messages.
I assume this is because of the iterative nature of solving. It bounces back and forth around the result at that load step, meaning it needs to be able to offshoot the maximum value, or the solver will fail.
I fix this by extending the strain curve beyond max. If for example the material typically ruptures at 30% strain, I need to have a curve that goes to 100% strain. Any load step results beyond that I have to sift through manually and discard. "I see that 30% strain occurred at X bar pressure".
However - due to modeling issues - simplifications and suboptimal constraints - quite often the results are like "I see that 30% strain occurred at the zone of interest, but my sloppy modeling caused it to also reach 60% strain somehere else". Whereupon I have to spend effort to remove those hotspots in order to get the zone of interest highlighted. It's a pain having to write in the report "Please disregard the screaming red zone to the left, that is just an artifact of user error".
So I keep doing lengthy simulations where I have to monitor the progress and interrupt when I suspect that things go awry, again and again.
Now - what I need are two things:
1 - Some method to create loads like "Increase this value for every load step until a max stress/strain/deformation/whatever of X is achieved, then stop the simulation". This way I don't need to sit and monitor the progress to stop it manually when it goes sideways.
2 - Some method to identify material failure. "Max strain Y in element Z, it is removed in the next load step". This would likely trigger an abrupt stop when the decreased load resistance rapidly cause a mass extinction of elements.
If any of those already exist, I do not find it. When I google it, I find that some people fix #2 there by writing their own ADPL scripts, which is way beyond my skill, and also unexpected. Such functionality is hardly more complicated than dozens of other functions for which there are GUI tools?
I appreciate any feedback on this. Thanks in advance!

[Ashish Khemka]

One option is to apply the load till the point where the strain reaches 30% strain. Even when the model reaches the last point on a multi-linear curve then you may see the error messages like element distortion. You may apply a lower load.
Regards Ashish Khemka