ASTM D 2240 : Standard Test Method for Rubber Property—Durometer Hardness

This test method covers twelve types of rubber hardness
measurement devices known as durometers: Types A, B, C, D,
DO, E, M, O, OO, OOO, OOO-S, and R. The procedure for
determining indentation hardness of substances classified as
thermoplastic elastomers, vulcanized (thermoset) rubber, elastomeric materials, cellular materials, gel-like materials, and
some plastics is also described.

Summary of Test Method

This test method permits hardness measurements based
on either initial indentation or indentation after a specified
period of time, or both. Durometers with maximum reading
indicators used to determine maximum hardness values of a
material may yield lower hardness when the maximum indicator is used

The procedures for Type M, or micro hardness
durometers, accommodate specimens that are, by their dimensions or configuration, ordinarily unable to have their durometer hardness determined by the other durometer types described. Type M durometers are intended for the testing of
specimens having a thickness or cross-sectional diameter of
1.25 mm (0.050 in.) or greater, although specimens of lesser
dimensions may be successfully accommodated under the
conditions specified in Section 6, and have a Type M durometer
hardness range between 20 and 90. Those specimens which
have a durometer hardness range other than specified shall use
another suitable procedure for determining durometer hardness.

Significance and Use

This test method is based on the penetration of a specific
type of indenter when forced into the material under specified
conditions. The indentation hardness is inversely related to the
penetration and is dependent on the elastic modulus and
viscoelastic behavior of the material. The geometry of the
indenter and the applied force influence the measurements
such that no simple relationship exists between the measurements obtained with one type of durometer and those obtained
with another type of durometer or other instruments used for
measuring hardness. This test method is an empirical test
intended primarily for control purposes. No simple relationship
exists between indentation hardness determined by this test
method and any fundamental property of the material tested.

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