ASTM D1415 – Standard Test Method for Rubber Property—International Hardness
Significance and Use
4.1 The International Hardness test is based on measurement of the penetration of a rigid ball into the rubber specimen under specified conditions. The measured penetration is converted into IRHD, the scale of degrees being so chosen that 0 represents a material having an elastic modulus of zero, and 100 represents a material of infinite elastic modulus.
4.1.1 The scale also fulfills the following conditions over most of the normal range of hardness: one IRHD range represents approximately the same proportionate difference in Young’s modulus, and for rubber vulcanizates in the usual range of resilience, readings in IRHD are comparable with those given by a Type A durometer (Test Method D2240) when testing standard specimens.
18.104.22.168 The term “usual range of resilience” is used to exclude those compounds that have unusually high rates of stress relaxation or deformational hysteresis. For such compounds, differences in the dwell time in the two hardness tests (Test Methods D2240 and D1415) result in differences in hardness values. Readings may not be comparable when testing curved or irregularly shaped test specimens.
4.1.2 For substantially elastic isotropic materials like well-vulcanized natural rubbers, the hardness in IRHD bears a known relation to Young’s modulus, although for markedly plastic or anisotropic rubbers the relationship will be less precisely known.
1.1 This test method covers a procedure for measuring the hardness of vulcanized or thermoplastic rubber. The hardness is obtained by the difference in penetration depth of a specified dimension ball under two conditions of contact with the rubber: (1) with a small initial force and (2) with a much larger final force. The differential penetration is taken at a specified time and converted to a hardness scale value.
1.2 This test method is technically similar to ISO 48.