IRHD Hardness - ISO 48
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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/E=0.0038r0.65*D1.35
where:
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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