ARDL performs International Hardness testing on material samples by indenting a material with a rigid ball in accordance with ASTM test procedures. With microhardness testing, there is a small initial force and then a larger “final” force measurement made. A conversion of the measured forces is performed and the measurements are then reported in IRHD results.
According to ASTM microhardness testing “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.”
Microhardness - Rubber
Standard Test Method for Rubber Property - International HardnessASTM D 1415