Rubber FEA & Hyperelastic Characterization of Elastomers and Rubber Materials
Hyperelastic Material Modeling using Ansys, Abaqus, Marc in Finite element analysis (FEA) software packages is widely used in the design and analysis of polymeric rubber and elastomer components in the automotive and aerospace industry. Test data from the major principal deformation modes are used to develop the hyperelastic material constants to account for the different states of strain.
1) Uniaxial Tension Tests
2) Planar Shear Tests
3) Volumetric Compression Tests
4) Uniaxial Compression Tests
5) Equibiaxial Tension Tests
1) Uniaxial Tension Test
Uniaxial tension is the mother of all mechanical tests and provides a very important data point regarding the strength, toughness and quality
of the material. ASTM and ISO standards provide the guidance to carry out the tests. The samples are designed so as the specimen length is larger than the width and thickness. This provides a uniform tensile strain state in the specimen.
2) Planar Shear Testing
Planar shear specimens are designed so that the width is much larger than the thickness and the height. Assuming that the material is fully
incompressible the pure shear state exists in the specimen at a 45 degree angle to the stretch direction.
3) Volumetric Compression Testing
The measure of compressibility of the material is testing using the Volumetric compression test. A button specimen is used and a hydrostatic
state of compression is applied on the specimen to evaluate it.
4) Uniaxial Compression Testing
Uniaxial compression refers to the compression of a button specimen of approx. 29mm diameter and 12.5 mm height. This test can be
effectively utilized to replace the expensive biaxial extension test through proper control of the specimen and testing fixture surface
friction and proper testing technique and methodology.
5) EquiBiaxial Tension Testing
Biaxial tensile testing is a highly accurate testing technique for mechanical characterization of soft materials. Typical materials tested in biaxial tension are soft and hard rubbers elastomers, polymeric thin films, and biological soft tissues.
The outputs from these tests are the stress vs strain curves in the principal deformation modes. Curve fitting is carried out on the experimental stress vs strain curves to generate the material constants.
These constants are obtained by comparing the stress- strain results obtained from the material model to the stress-strain data from experimental tests. Iterative procedure using least-squares fit method is used to obtain the constants, which reduces the relative error between the predicted and experimental values. The linear least squares fit method is used for material models that are linear in their coefficients e.g Neo-Hookean, Mooney-Rivlin, Yeoh etc. For material models that are nonlinear in the co-efficient relations e.g. Ogden etc, a nonlinear least squares method is used.