Question regarding how to input material properties parameters when density is missing (Ogden law42)

Goutham Sridhar_21603

Hello,

I'm doing a simulation with a verification model for ogden material with cylic displacement controlled loading, and I don't have information regarding the mass or density of the material. All I have are the below information in the table. I want to know what value of density should I input and how to input the relaxation times (and in which parameters of law42 does it correspond to) given in Figure 3 so that I get the results in figure 4. 

 

   

 

 

The reference is: Holzapfel, G.A.: On large strain viscoelasticity: continuum formulation and finite element applications to elastomeric structures. International Journal for Numerical Methods in En... Article  in  International Journal for Numerical Methods in Engineering · November 1996 DOI: 10.1002/(SICI)1097-0207(19961130)39:22<3903::AID-NME34>3.0.CO;2-C

 

I also want to reproduce the hertz contact simulation on this site: https://github.com/KratosMultiphysics/Examples/blob/master/contact_structural_mechanics/validation/hertz/README.md

 

I have the same problem of not having the density values here and I don't know which material law to use in this case.

 

Please help me out in resolving the issues I'm facing.

 

Looking forward to your response.

 

Thanks a lot for taking the time and your support.

 

Best regards,

Goutham.

PaulAltair

For Density, if you don't know for sure, use something physically appropriate, if you know what the material is, use something similar. 

The data looks like it from static/quasi-static testing, Radioss usage is usually high speed/dynamic/impact events, if you are looking to simulate a longer term scenario, OptiStruct may be a better choice? (and in this case, for quasi-static loading, density is not needed)

Goutham Sridhar_21603

Hello Paul,

Thanks for your message. Yes, I'm trying to do quasi-static simulations.

I have to do the simulation on Radioss, I don't have a choice on the solver. The material is rubber, but the density isn't given. My supervisor told me to use the density value of water since we are trying to model a nearly incompressible material (for soft tissues).

 

For the hertz contact problem, which density values should I use for the 2 parts in contact with different E and nu values since the material is elastic & not incompressible?

PaulAltair

Goutham Sridhar_21603 said:

Hello Paul,

Thanks for your message. Yes, I'm trying to do quasi-static simulations.

I have to do the simulation on Radioss, I don't have a choice on the solver. The material is rubber, but the density isn't given. My supervisor told me to use the density value of water since we are trying to model a nearly incompressible material (for soft tissues).

 

For the hertz contact problem, which density values should I use for the 2 parts in contact with different E and nu values since the material is elastic & not incompressible?

I'm not sure what you mean exactly, Hertz contact is only available for 2nd order thick shells in Radioss, and Density isn't an input to the contact (only the 2 brick groups + friction). You wouud need densities for the material though. What is the other contacting entity? If water density (typical values: 1g/cm^3 1e-9T/mm^3 1e-6kg/mm^3) is ok for the rubber, then steel would be 7.8x that for example, Aluminium 2.7x.