How to Calculate Compression for Viscoelastic Material

Certain types of rubber exhibit properties of a viscoelastic material.

A viscoelastic material is one that has elastic and viscous properties when a force is applied to the material; that is, it can act as a solid or a fluid, depending on the current or past forces applied to it. Viscoelastic materials can have very complicated properties; however, the compression (i.e., the change in volume of an object when acted upon by a force) can be calculated without knowledge of these complicated properties.

Things You'll Need

• Measuring tape
• Compression machine

Instructions

1. Determine the volume of the object using the geometric properties of the object. For example, if the object is a sphere, measure the radius of the object, then calculate the volume from this number. Assuming a radius of 0.23 meters, the volume can be calculated by multiplying 1.333, pi and the cube of the radius (i.e., the radius multiplied by itself twice) together. In this example, this means 1.333 x 3.14 x 0.23 x 0.23 x 0.23 = 0.051 meters cubed (m^3).

2. Using a compression machine (typically found in engineering machine shops), uniformly compress the object to the desired volume, then measure the radius of the object. For example, if the compressed object has a radius of 0.18 meters, the volume will then be 0.024 m^3, which is found using the formula outlined above for determining the volume of a sphere.

3. Subtract the deformed volume of the object from the original volume of the object. In this example, subtracting 0.024 m^3 from 0.051 m^3 gives 0.027 m^3. This is the compression of the viscoelastic material.

Tips & Warnings

• As many viscoelastic materials will change their material dimensions after the compressive force is removed, make any measurements immediately after the force is applied.

References

• The University of Auckland: The Response of Viscoelastic Materials
• Massachusetts Institute of Technology: Stress-Strain Curves