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IndiaRubberDirectory.com > Rubber Engineering > Elastromer Properties |
Elastomer Properties - Shear Modulus/Tear Strength/Dynamic Stress-Strain
Shear Modulus: The shear modulus
is an important property in design calculations for elastomers used in shear.
The test methods typically require that the test sample be bonded to metal
plates. The resulting ratio of the shear stress to shear strain is the shear
modulus.
Test Methods:
Tear Strength: For
considerations of removing a molded part from the production mold, or for
determining the ease of which a tear can start and propagate in application,
tear strength is an important property. Different test methods use different
shapes and methods for applying a tearing force.
Test Methods:
Dynamic Stress-Strain: In cyclic
or dynamic applications, the viscoelastic properties of elastomers are very
important. Lost energy, in the form of heat, arises from molecular friction as a
result of an applied load. The percentage energy loss per cycle is known as “hysteresis.”
When the loading and unloading cycle continues, the shape and position of the
hysteresis curve changes.
The response of a specimen to a sinusoidal
deformation can best exhibit the dynamic properties of an elastomer. The elastic
component of the elastomer is responsible for the in-phase stress, while the
viscous component is responsible for the out-of phase stress. The amount by
which the strain response lags the resultant of the two stresses (in-phase and
out-of-phase) is known as the phase or loss angle, š. The more viscous an
elastomer, the greater the phase or loss angle. The tangent of this angle “tan
š,” in the simplest terms, is the ratio of the viscous modulus to the elastic
modulus.
Dynamic Properties for Various Sealing Elastomers
PROPERTY |
AEGIS |
Fluoroelastomer |
EPDM |
Nitrile |
Silicone |
Fluorosilicone |
Tensile Strength |
Good |
EXCELLENT |
EXCELLENT |
EXCELLENT |
Fair |
Fair |
Abrasion Resistance |
Fair |
Good |
Good |
Good |
Poor |
Poor |
Tear Resistance |
Fair |
Fair |
EXCELLENT |
EXCELLENT |
Poor |
Poor |
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