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date: 19 February 2025

International Rubber Hardness Degrees (IHRD) 

Source:
A Dictionary of Mechanical Engineering
Author(s):

Marcel Escudier,

Tony Atkins

An alternative to the Shore hardness for quantifying the hardness of elastomeric or rubber materials. The IRHD value is related to the depth of penetration into a flat specimen of a spherical indenter under a defined force. An IRHD value of 0 corresponds with a zero Young’s modulus, while an IRHD value of 100 corresponds with an infinite Young’s modulus. There are four methods for the determination of standard hardness: method N (normal test) for 30 IRHD to 95 IRHD using a 2.5-mm-diameter sphere; method H (high-hardness test) for 85 IRHD to 100 IRHD using a 1-mm sphere; method L (low-hardness test) for 10 IRHD to 35 IRHD using a 5-mm sphere; and method M (microtest) which is essentially a scaled-down version of method N for the testing of thinner and smaller test pieces with 30 IRHD to 95 IRHD using a 0.395-mm sphere. The total force applied to the indentor is 5.7 N for the first three tests and 0.153 N for the microtest. Modifications of the four methods are used for the determination of the apparent hardness of curved surfaces. The relevant ISO standards are ISO 48-1, 48-5, and 48-6.... ...

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