Standard Test Method for Stiffness Properties of Plastics as a Function of Temperature by Means of a Torsion Test

Abstract

4.1 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. 4.2 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 it is possible that the specimen will be deflected beyond its elastic limit, the calculated value will not always 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, it is possible that there is 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 D4000 lists the current ASTM material standards. 4.3 This test method is useful for determining the relative changes in stiffness over a wide range of temperatures.