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ERROR in an Elastoplastic problem
Posted 20 sept. 2011, 05:44 UTC−4 Version 4.1 3 Replies
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I’m trying to solve an elasto-plastic problem in 3D.
I want to define the plastic performance of the material by Johnson & Cook’s law. This law says that the Yield Stress depends on temperature, plastic strain and strain rate.
To simplify the problem, at first I am going to introduce only the dependence with the plastic strain (avoiding strain rate and temperature).
So the constitutive equation is:
Yield stress=A+B*plastic_strain^n
Where A [MPa], B [MPa] and n [ ] are material constants.
In COMSOL, defining the plasticity model:
- Yield stress level=A
- Isotropic hardening -> Hardening function=B*mod1.solid.epe^n
The value of “n” is 0,26.
When the model is solved I get the ERROR that follows:
“Attempt to evaluate negative power of zero.
- Function: ^
Failed to evaluate temporary symbolic derivative variable.
- Variable: mod1.solid.sY@VDN$mod1.solid.epe
- Defined as: (((mod1.solid.epe^(n-1))*n)*B)
Failed to evaluate expression.
- Expression: d(d(mod1.solid.sY^2,mod1.solid.sY),mod1.solid.epe)”
But this error doesn’t occur when n>=1.
What could be the possible reason for this error? How could I avoid it?
Thanks!
Itxaso
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Yield stress = A + B*(plastic_strain + residual_plastic_strain)^n
where residual_plastic_strain is a small number that helps avoid the singularity.
Nagi Elabbasi
Veryst Engineering
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I applied what you said and I got another error message:
"Attempt to evaluate non-integral power of negative number"
so in order to avoid negative numbers (plastic strain sometimes becomes slightly negative...), I defined the equation as "A+B*abs(solid.epe)^n". But it appeared again the first error...
Finally, my equation is:
A+B*(abs(solid.epe)+epsilon)^n
.
and now it works!
Itxaso
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A+B*(abs(solid.epe)+epsilon)^n
when i added strain rare variable(eperate), with defining arguments for strain and strain rate as 1,1/s
i got following error
Function called with wrong number of arguments.
- Function name: comp1.mat5.ElastoplasticModel.sig_h
- Number of arguments used: 1
- Number of arguments expected: 2
I am not able to identify the error.