Yeoh Model Parameter

Greetings,

I'm conducting a simple shear test (single lap joint) between aluminum bonded with 3M adhesive. 

Adhesive material is 3M VHB 4930 adhesive (acrylic)

Result obtains = 

Load vs Displacement Curve

True Stress vs Stretch Ratio

From the literature, mostly they used Yeoh model for 3M adhesive (Modeling and simulation of dielectric elastomer actuators,M.Wissler 2005).

The material constant for C10, C20, C30 I get from the curve fitting equation from the True Stress vs Stretch Ratio.

Then, from the material constant I input on Abaqus software to run the FEM analysis.

C10 = 1.774 MPa

C20 = - 4.669 Mpa

C30 = 39.24 MPa

D1 =?

D2 =?

D3 =? 

My question, how can i get material constant for D1, D2, D3? And D1, D2, D3 represents what?

Could you please give me an explanation.