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# Van der Waals Material Properties

The Van der Waals material model is a hyperelastic material model and is available for 2D, brick and tetrahedral elements. The material properties are listed below.

Click the Curve Fit button on the Element Material Specification dialog to use the Curve Fitting routine. This routine calculates the material constants using measured stress-strain data.

The potential function of the Van der Waals material is as follows:

where

Material Properties:

• Mass density: The mass density of a material is its mass per unit volume. Mass density is applicable to all structural elements. This property is required in all MES/ nonlinear structural analyses involving gravity or acceleration loads.
• Shear modulus: The shear modulus (m).
• Locking Stretch: The locking stretch (lm) accounts for finite extendibility of the non-Gaussian chain network. In contrast to the Arruda-Boyce model, the mathematical structure of the Van der Waals potential is such that the strain energy tends to approach infinity as the locking stretch is reached. Thus, the Van der Waals potential cannot be used at stretches larger than the locking stretch.
• a: Global interaction parameter. Given Mooney-Rivlin coefficients and a locking stretch, a suitable value for the global interaction parameter is:

where µ is the initial shear modulus at low strains and C01 is the second Mooney-Rivlin parameter.
• Beta: This parameter (b) represents a linear mixture parameter combining both invariants and into . The parameter β represents a linear mixture parameter combining both invariants and the admissible values are 0 ≤ β ≤ 1.
• Bulk Modulus of Elasticity: The bulk modulus (K) relates the change in volume to the applied pressure. It equals -pressure/(volumetric strain), where the volumetric strain equals the change in volume divided by the original volume. The bulk modulus of elasticity can also be found from the following equation: E/3*(1-2v) where E is the modulus of elasticity of the material and v is Poisson's ratio of the material.