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Hi all, I am doing a contact simulation and would like to obtain the total area in contact. I am able to get an output using: ************************ *Output, history *CONTACT OUTPUT, MASTER=masterSurf, SLAVE=slaveSurf CAREA ************************ However, the output is a single integer...

I'm done, thanks again! Note: my directions are backwards in the analytical model; I'm checking to see why, but not a big problem.

Eureka! I just finished implemented the changes to the Mathematica code and checking against Abaqus. Using the 'sigma-transverse == 0' equations, the system is harder to solve, so I have to work out a new method for fitting the parameters. I can deal with that however. @IceBreakerSours: I...

I'm using cylindrical because the final mesh will be round (see images above). Using cylindrical coordinates, I don't have to define a local material orientation for each element; I simply assign the coordinate system and move forward. I'm doing it in the validation just to make sure it works...

Excellent! I never thought to use sigma_2 == 0 when solving for sigma_1 as a function of lambda_1! Yes, Mathematica should have no problem with this. I can't wait to try this. I owe you both, you have been incredibly patient and helpful!

UPDATE: Yes, I believe this is the problem! I made the assumption that in uniaxial tension in the lambda_1 direction, lambda_2 = lambda_3. However, since the material is anisotropic, my intuition suggests this to be incorrect. The constitutive equation for incompressibilitiy should still...

@sdebock, Thank you for trying the input file! By lambda_t, do you mean the theta direction? I stretch the 10x10mm element 1.5mm in each direction (one per file), which should yield a lambda_t of 1.15. Can you clarify why you get a lambda_t of 1.3? How did you get lambda_x from the output? Do...

Hey again, I added the constraints for the rotational degrees of freedom where they were missing as IceBreakerSours suggested. The 'kappa' I am using is consistent with the example I found in the documentation. The mathematical model also seems to work okay with this value. I'm still getting...

Thank you both! Yes, I meant to ask what 'S' in Abaqus CAE represents. Thank you for confirming sdebock. I'll try constraining the rotational degrees of freedom as suggested by IceBreakerSours. I didn't think that a uniaxial displacement would have any influence on the node rotations.

Not yet. I'm reading Holzapfel's book over Christmas break so I understand the fundamentals better. I found other sources saying that S is Cauchy, but I need to check the documentation.

I figured out which elements may be used with incompressibility by trying a C3D8 element and getting this error: Looks like shell elements are okay. The final geometry we will be using is a 3D surface with uniform thickness, so shell elements are the most convenient. That's why I've been...

I checked both the .msg and .dat files and couldn't find the suggested warning. Also, in the Abaqus documentation example, they suggest that D=0 is acceptable: Anyways, small changes to the compressibility do yield large changes in material response. Have you seen this paper? Its very recent...

Ah yes, E_alpha is positive for all lambda except for extreme cases of gamma, so that should be okay. In that case I must be doing something else wrong; I'm verifying against Abaqus using a single 10x10mm shell element in tension. I displace one side of the element by 1.5mm, yielding a stretch...

Thank you all again, I have made progress using the HGO model. I'm still having trouble fitting parameters to my data. The form of the strain-energy density function seems a little weird to me. If I understand correctly, the Cauchy stress 'sigma' in the 11 direction would be: sigma_11 =...

Edit 2: I'm looking in the 6.12 documentation for HGO now to see how the fiber orientations are specified. Here is the desired behavior of the material model. You can see that both curves are highly non-linear, with the longitudinal direction about twice as distensible as the circumferential...

Edit: I made this simplified model to explain. The actual model includes multiple branches and is not as uniform.

@IceBreakerSours By "bifurcations", I mean that the vein branches. I should actually call them anastomoses I guess (joining of two smaller veins to form a larger vein). I've been defining a local cylindrical coordinate system for each branch up to now, which has worked out okay. I'll see how it...

@ IceBreakerSours: The reason I moved away from the HGO model is that I had trouble getting two material orientations for the fibers using CAE. When you say "allow two directions of anisotropy", do you mean specifying "Number of local directions" to be two? Would I then specify two sets of...

Thanks Mechlrl, that helps. I saw that 'D' was temperature dependent in the documentation and didn't interpret that correctly. Incompressibility is often assumed for veins since they are mostly water; now I can justify using 0 correctly. The root of the issue is that biaxial test data for this...

I am working on modelling the response of an orthotropic hyperelastic material (vein) to a given load. Because the local thickness of the material is unknown, shell elements with a constant thickness are used. I am able to get the simulation to run. However, I had some questions about the...