Bergstrom-Boyce (/MAT/LAW95)
This law is a constitutive model for predicting the nonlinear time dependency of elastomer like materials. It uses a polynomial material model for the hyperelastic material response and the Bergstrom-Boyce material model to represent the nonlinear viscoelastic time dependent material response.
This law is only compatible with solid elements.
Material Parameters
- and
- Material parameters

Since , then and total stress is .

- Yeoh: Where, are not zero.Figure 4.
- Mooney-Rivlin:
Where, and are not zero and .
- Neo-Hookean:
Only and are not zero.
- and
- Material parameters which can be calculated by completing a curve fit for quasi-static material test data.
RD-E: 5600 Hyperelastic Material with Curve Input, contains a curve fit example for Mooney-Rivlin and Yeoh material models. can be calculated from the bulk modulus or left blank.
If the bulk modulus of the material is known, can be calculated, or if =0, an incompressible material is assumed.
Viscous (Rate) Effects
- Effective stress in Network B.
- , and
- Input material parameters.
The material constants , and are limited to a specific range of real values as defined in the Reference Guide. If limited data is available, a trial and error method 1 could be used to determine these constants. Start with the default values of , =1.6; and =5. Next, compare model predictions with experimental data for at least one strain rate and adjust to get a fit for the strain rate data.