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Inconsistent units in a hyperelastic material model
Posted Nov 13, 2014, 9:54 a.m. EST Structural Mechanics Version 4.4 2 Replies
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Hi,
I am trying to create a user defined hyperelastic material model. For the isochoric strain energy density (Wsiso) I defined two different terms, Wf and Wm in the following way:
Wf = (1/2)*(c1/c2)*(exp((c2*(sqrt(i4)-1)^2))-1)
Wm = (u/2)*(i1-3)-u*log(sqrt(i3))
c2, i4, i1, and i3 are unitless
c1 and u have the unit [MPa]
In the variable section I can see that COMSOL displays Wf as having the unit [Pa] (which is expected) but Wm has the unit [m]. Since Wsiso = Wf+Wm, I get a error message saying "Inconsistent unit" because Wf is in pascal and Wm is in meters.
It surprises me that Wm is in meters since it only contains the variables u [Mpa] and i1, i3 [unitless]. Looking at the equation the expected unit would be [Pa].
Can anyone help me with this problem
Thanks in advance,
Brynjar
I am trying to create a user defined hyperelastic material model. For the isochoric strain energy density (Wsiso) I defined two different terms, Wf and Wm in the following way:
Wf = (1/2)*(c1/c2)*(exp((c2*(sqrt(i4)-1)^2))-1)
Wm = (u/2)*(i1-3)-u*log(sqrt(i3))
c2, i4, i1, and i3 are unitless
c1 and u have the unit [MPa]
In the variable section I can see that COMSOL displays Wf as having the unit [Pa] (which is expected) but Wm has the unit [m]. Since Wsiso = Wf+Wm, I get a error message saying "Inconsistent unit" because Wf is in pascal and Wm is in meters.
It surprises me that Wm is in meters since it only contains the variables u [Mpa] and i1, i3 [unitless]. Looking at the equation the expected unit would be [Pa].
Can anyone help me with this problem
Thanks in advance,
Brynjar
2 Replies Last Post Nov 14, 2014, 9:21 a.m. EST
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Posted:
10 years ago
Hi,
Try renaming the variable 'u'. It seems like you have a conflict with the X-displacement 'u' which has unit [m].
Regards,
Henrik
Try renaming the variable 'u'. It seems like you have a conflict with the X-displacement 'u' which has unit [m].
Regards,
Henrik
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Posted:
10 years ago
Thank you Henrik, it worked!
Regards,
Brynjar
Regards,
Brynjar