Data for Hyperelastic Materials Models : Modelling : Measurement Techniques : Advanced Materials : Science + Technology : National Physical Laboratory

Data for Hyperelastic Materials Models

Hyperelastic data for a flexible
material - comparing measured
and predicted data from single
element biaxial tests In hyperelastic materials models the strain energy density is modelled as a function of the deviatoric (shear) and volumetric components of the strain tensor. A common assumption made, particularly for rubbers, is that the material is incompressible. Therefore, the volumetric terms can be set to zero. Only the shear terms need be considered. However, this assumption may not strictly hold for all flexible materials.

It is suggested that test data are obtained under conditions of plane stress (uniaxial tension), plane strain (planar tension), equi-biaxial stress (equi-biaxial tension) and volumetric compression in order to accurately model the hyperelastic materials under multi-axial states of stress. NPL have developed test methods for obtaining reliable input data. Links to some relevant reports are provided at the end of the page.

The cure state of the bulk test specimens used to obtain the mechanical properties data should be similar to that of the adhesive in the bonded structure. Cure schedules should be selected to ensure that the thermal history of the materials are similar in each case. Dynamic Mechanical Thermal Analysis (DMA/DMTA) measurements can be made to compare the state of cure of the materials.

Materials such as flexible adhesives are likely to have strain rate and temperature dependent properties. Tests for characterising the properties for the hyperelastic models must be carried out at the same temperature and at comparable strain rates.
FEA programmes such as ABAQUS use least squares fitting routines to calculate the model coefficients that describe the hyperelastic behaviour. The accuracy of the model can be tested through single element tests.