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[Haiquan]

Hello 

I used Generalized Time Hardening creep model for product made of polymer ABS/PC, but I face convergence issue(simulation condition is under 85°C uniform temperature), the creep integration algorithm does not converge. More substeps had been used and creep limit ratio was set to 10.
The fitting result of test data is shown below, there are negative constants and a warning shown that this could cause negative creep strain in the solver.
I tried to validate my creep model using a simple rectangular specimen, there is no convergence issue, and the simulation result matched the test data as shown below.
What is the root cause of this convergence?

 

 

 

[peteroznewman]

How much does setting the negative constants to zero change the quality of the fit?  If not too much, does that improve convergence?

[Haiquan]

Hello Peteroznewman

Thank you very much for your comment.

I tried your suggestion, and set the negaptive constant C2 to 0 for rectangular specimen under 110°C condition(no convergence issue for this simple case too). But simulation result shown significant difference, even the absolute value of C2 is much smaller than C1, C4 and C5