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.
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