Instruments as per ASTM D1415
Standard Test Method for Rubber Property—International Hardness
The ASTM D1415 standard covers a process of measuring the stiffness of thermoplastic or vulcanized rubber. The hardness is measured by analyzing the difference in the penetration profundity of a specified dimension ball under two test conditions of contact with the rubber: (2) with a small original force and (1) with a final bigger force. The differentiated penetration is considered in a specific period of time and value is measured with a hardness scale. This test procedure is similar to ISO 48.
The hardness test as per international standard is based on measurement of the penetration of a rigid ball into the rubber sample under specified conditions. The measured penetration is hence transformed into IRHD. The IRHD scale of degrees represents 0 as a material with elastic modulus of zero and 100 replicates a material with infinite elastic modulus.