The property measured by this test is the apparent modulus of rigidity, G, sometimes called the apparent shear modulus of elasticity. It is important to note that this property is not the same as the modulus of elasticity, E, measured in tension, flexure, or compression. The relationship between these properties is shown in Annex A1.

The measured modulus of rigidity is termed “apparent” since it is the value obtained by measuring the angular deflection occurring when the specimen is subjected to an applied torque. Since the specimen may be deflected beyond its elastic limit, the calculated value may not represent the true modulus of rigidity within the elastic limit of the material. In addition, the value obtained by this test method will also be affected by the creep characteristics of the material, since the load application time is arbitrarily fixed. For many materials, there may be a specification that requires the use of this test method, but with some procedural modifications that take precedence when adhering to the specification. Therefore, it is advisable to refer to that material specification before using this test method. Table 1 in Classification D 4000 lists the current ASTM materials standards.

This test method is useful for determining the relative changes in stiffness over a wide range of temperatures.

1.1 This test method covers the determination of the stiffness characteristics of plastics over a wide temperature range by direct measurement of the apparent modulus of rigidity.

1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Note 1—This test method is not equivalent to ISO 458/1:1985 or ISO 458/2:1985 and results cannot be directly compared between the two methods.