Learning Forum

[malhamah]

Hello all. I need your help in imposing a constraint to a structural simulation in ANSYS MAPDL.

This model uses temperature results generated from a different (thermal) model as input, and the results so far are promising. However, I need to impose a boundary condition whereby when a certain temperature is reached, instantaneous annealing and creep occur. In other words, the stress and all components of strain (plastic, thermal, etc.) on an element need to be reset to zero when the temperatures at all Gauss points of this element exceed a certain value (Trelax).

Can you please assist me in imposing this condition? I cannot seem to find a way to impose values to stress and strain, as they are usually output values that are not directly controlled by the programmer. Thank you for your time.

[Sheldon Imaoka]

This is usually accomplished through a feature called "element birth and death". If you are using Mechanical, it's a condition you can apply; if you're using Mechanical APDL, it's the EKILL and EALIVE commands.
If you are imposing the temperature, you know the temperature history - you can use a separate load step when you are imposing a temperature above your Trelax value to deactivate the elements. Then, you use a third step to 'reactivate' the elements in a stress-free condition. This requires at least 3 steps (2nd step to 'deactivate' the elements, 3rd step to 'reactivate' the elements with no stress or strain history). Note that if you do have loads applied when the elements reactivate, they may not have exactly zero stress and strain, so the resetting of the stresses and strains to zero occurs, but if you have thermal expansion or gravity or other loads applied, you may see non-zero values in the 3rd step.
Regards Sheldon