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Elastomer Properties - Bulk Modulus/Resiliency

Elastomers are often treated as incompressible materials for analytical convience. However, in many instances the compressive response of elastomers is very important.

Bulk or Static Modulus. The bulk modulus is a property of a material which defines its resistance to volume change when compressed. It can be expressed as:

K = p/ev

Here p is the hydrostatic pressure, ev is the volumetric strain and K is the bulk modulus. In practice, a positive volumetric strain is defined as a decrease in volume.

Measuring a material’s strain response to an applied pressure is a simple test for bulk modulus. The bulk modulus can be expressed as the derivative (slope) of the pressure-strain curve.

Relationships between Young’s modulus E, the shear modulus G, and Poisson’s ratio v are related by:

• E = 3 K (1 – 2v)
• E = 2 G (1 + v)

Test Methods:

• ISO 7743
• ASTM D575

Rebound Resilience. When a pendulum hammer impacts a rubber specimen from a certain distance or angle, the degree or distance that the pendulum does not return is an indication of the energy lost during the deformation.

Test Methods:

• ISO 4662
• ASTM D1054, D2632

Next topic Elastomer Properties - Compression Set/Creep

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