Patran/Marc Isotropic ,Plastic deformation

[Rob767]

Hi my project is to predict accurately the stress distribution in a rod in tension (non-linear, plastic behaviour).

I am user Patran and Marc as the solver. I am having a hard time finding a converging solution.
I have played with a lot of load increment parameters and iteration parameters. If i change one parameter minutely ( e.g time step) i get a completely different solution.

I have even tried refining the mesh and imposing severe criteria on the parameters and the result is always different from one test to another.

If anyone has any tips to guide me in the right direction i would really appreciate it. Thanks

 

[feadude]

If you are using perfectly plastic material stress/strain curve ie zero slope after yield since you have a rod in tension you could get unreliable answers, this is because there is no increase in stress after the material yields and strain keeps on increasing. However based on FEA formulations this can not be. So give the after yield a slight slope and see if you get consistent answers. If you had a beam in bending you can have zero slope after yield but not in simple tension.

 

[BuckTU]

Try to use a static loadcase type with arc lenght adaptive, if you are using constant time steps.

Otherwise you have to explain what kind of FEM appraoch you're taking to give us the tools to see what your doing "wrong".