Elastomeric Sponge (foam) Characterization

Introduction

The analysis of elastomeric sponge materials in finite element analysis sometimes require the use of hyperelastic material models, sometimes require the use of special sponge models and sometimes may be adequately modeled with simplistic spring models. The defining factors are the extent to which the sponge is compressible and the extent to which the foam is compressed in the application. Most complex material models benefit from experimental data in more than one state of strain. If the sponge elastomer is going to be modeled as a dense elastomer, the basic simple tension, planar tension and equal biaxial test data sets described in the elastomer section may be appropriate. Other experiments that may prove helpful are listed below.

There are 3 strain states which are particularly useful in characterizing sponge (foam) elastomers. They are simple tension with lateral strain measurements, simple shear and simple compression.

Typical Foam Elastomer Experiments:

  • Simple Compression
  • Simple Shear
  • Tension with Lateral Strain Measurement


  • Simple Compression

    The compression experiment is also a popular test for elastomers. When testing for analysis, pure states of strain are desired and this is especially difficult to achieve experimentally in compression for dense materials. However, for foam materials, the error due to friction between the specimen and platen is not as significant. Often, the only experiment needed is a simple compression test.

     

    Image of a soft foam in compression.
    Soft Open Cell Elastomers Foam in Compression

    Simple Shear

    The simple shear experiment is ideal for soft elastomer foam materials where it is often possible to bond or glue the specimen to fixtures.

    er experiment.
    Simple Shear Test Schematic

     

    Image of a simple shear experiment.
    Thin Closed Cell Foam Rubber in Simple Shear

    Tension with Lateral Strain Measurement

    The simple tension experiment for foam elastomers is made somewhat more complex with the addition of lateral strain measurement. This is necessary because the relationship between axial and lateral strain is needed.

     

    Image of a lateral and axial strain using a camera on a sponge tensile strip.
    Foam Strip in Tension with Lateral and Axial Strain Measurement using a Video System