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
• Low Mass Drop Test
• Tension with Lateral Strain Measurement

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.

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

Simple Shear Test Schematic

The low mass drop test is ideal for soft elastomer foam materials where it is desirable to achive a high velocity and also witness a rebound. Displacement is captured with a high speed laser sensor. Force and acceleration are captured with piezo sensors.

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.