Rubber Material Modeling using Abaqus

[sandeep18784]

Hello Dr. Jorgen

I am very new to Rubber material in Abaqus. I am reading Abaqus manuals and till now I only know, there are two methods to define Hyperelasticity. Either you can choose 'Starin Energy Potential' and define temperature dependent material parameters. And other one is using Test Data if available. I have two questions according to both,

1. I have EPDM rubber material with parameter hardness only. I have converted that into Young's modulus. Now how should I convert that into different material dependent parameters if I model hyperelasticity using Starin Energy Potential (MR, NH etc). Again which parameters are need to be consider during modeling.

2. Now I have Force-displacement data for Axial loading. I converted that into Nominal stress-Nominal strain data. Again which parameters are need to be consider in this approach.

I know I have very little knowledge at this time but I am damn sure when I will know, which parameters are need to be consider, it will be easy for me.

Help will be appreciated

Thank you

[farezehiri]

How did you convert hardness parameter to young modulus?

Which empiricial formula did you use?

Can you explain?

And is it Shore A or Shore D

[sandeep18784]

Hello farezehiri

The material which I have is EPDM rubber, shore A with hardness 40 to 90. And you will get many literature on internet for the empiricial formula to convert hardness parameter to young modulus. One of i got is,

http://www.sciencedirect.com/science/article/pii/S0109564109001237

Do you know the further procedure??

[sandeep18784]

Hello Dr. Jorgen

I have uniaxial test data for my hyperelastic material simulation in abaqus as nominal stress-nominal strain. Model is like, I have rubber material geometry which is quite difficult to mesh using Hexa elements so I meshed that using quadratic tetrahadron and as per abaqus documentation I used C3D10MH element type. "Smooth i kept blank, Strain energy potential i kept unknown and Poissons ration is 0.5". The load is applied by the rigid plate from up side which i meshed using Hexa with element type C3D8H. And the contact is defind between two. Rubber material geometry is fixed on bottom face in all DOF and the Rigid plate is fixed in X and Z direction so that it can move only in Y direction. But when i simulate it is not converging and stops without givivg any error messages. But I have warnings as,

1) ***WARNING: THE SPECIFIED HYPERELASTIC MATERIAL IS UNSTABLE. --- MORE
INFORMATION CAN BE OBTAINED BY SETTING *PREPRINT, MODEL=YES

2) ***WARNING: DEGREE OF FREEDOM 4 IS NOT ACTIVE ON NODE 24073 - THIS BOUNDARY
CONDITION IS IGNORED

and there is error in msg file as,

***ERROR: TIME INCREMENT REQUIRED IS LESS THAN THE MINIMUM SPECIFIED

About second warning, it gives this warning for all boundary conditions of Rubber geometry i.e for 456 and for Rigid plate i.e for 456. I think those elements don't have 456 dof, so its ok.

Dr. Jorgen Can you help me through this. What might be the problem you think.

Help will be appreciated.

[Jorgen]

It sounds like you are doing it right. I would try to run the simulation again using a very simple hyperelastic material model, for example the Neo-Hookean material model (which is known to always be stable).

-Jorgen