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IRHD Hardness - ASTM D1415

IRHD: International Rubber Hardness Degrees

A measure of the indentation resistance of elastomeric or rubber materials based on the depth of penetration of a ball indentor.

An initial contact force is applied to an indentor and the penetration is set to zero. The force is increased to a specified total load and the depth of penetration is measured. The IRHD value is related to the depth of indentor penetration.

For highly elastic materials, IRHD and Shore A are comparable.

An IRHD value of 0 represents a material with an Young's Modulus of zero and an IRHD value of 100 represents a material with an infinite Young's Modulus.

The relationship between the depth of penetration (hardness) and the IRHD number is based on:
F is the indentation force in Newtons,
E is the Young's Modulus in MPa,
r is the indentor ball radius in mm, and
D is the depth of penetration in mm.

Test Ball Diameter (mm) Contact Force (N) Total Force (N) Thickness (mm) IRHD Range
N (Normal) 2.5 0.3 5.7 4 30 to 95
H (High-Hardness) 1.0 0.3 5.7 4 85 to 100
L (Low-Hardness) 5.0 0.3 5.7 6 10 to 35
M (Micro) 0.395 0.0083 0.153 4 30 to 95

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