How to calculate strain rate in VUMAT? 2

[tyzhang]

Dear community,

I need to implement strain rate effect through VUMAT and I need to calculate strain rate in my VUMAT code. I read the VUMAT documentation and found two time-related variables: stepTime and dt. It seems that both variables can be used for the aim. T think that the strain rate can be calculated as follows,

strainRate = strainInc/stepTime
or
strainRate = strainInc/dt

The question is which one is correct, or neither of them is correct. Does anyone know this? Much appreciate.

 

[FEA way]

I would use the second version since it matches the definition of the strain rate.

 

[tyzhang]

Thanks for your comment. Why doesn't first one match with the def of strain rate? In the manual, 'stepTime' is Value of time since the step began. It also represents the length of time corresponding to the current strainInc.

 

[FEA way]

Because strain rate can be defined as ε_r = dε/dt and this dt is essentially the same as the one available in Abaqus. But to make sure you can run a simple test case for which the strain rate is known and calculate it in both ways in Abaqus.

 

[IceBreakerSours]

Step time is time accumulated since the current step began which is meaningless for defining any instantaneous rates whereas dt is precisely what you want. Write out the variables and look at the values.

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[tyzhang]

Thanks for your comments guys. My problem is solved now.