Post processing script to evaluate maximum stress range from a selected range of solution steps

Z.Boe

Hi everyone,
In multi-step analysis(e.g transient thermal), it is difficult to find the critical steps for a fatigue evaluation. A max. stress over time is not enough an done needs to do the "solution combination" between two time steps and if we have more than 2 or 4 time steps, the number of solution combinations increases rapidly.
Does anybody have a solution or tips. Thank you in advance.

Mike.Thompson

The short answer is using DPF for post processing evaluations. You can use "time scoping" concepts to determine which time steps you want. If you don't know from the start, you can simply get all of them, and then start evaluations that take differentials between them to identify the typical range that fatigue calcs require. There are many posts/examples of DPF otherwise, but you would mostly be looking for stress operators. There are operators for the 'stress" in tensor form, or you can operate on "invariants" like principal, or EQV stress.

Most typically you may want to take stress differentials based on the tensor components, then determine the critical range and finally do a von mises operator on the tensor.

Stress Range = EQV(Stress_Max_Tensor - Stress_Min_Tensor), where max and min are distinct time points as determined by your own logic, and may be variable from node to node.