Shear modulus is a material property useful in calculating compliance of structural materials in torsion provided they follow Hooke'law, that is, the angle of twist is proportional to the applied torque. Examples of the use of shear modulus are in the design of rotating shafts and helical compression springs.

Note 3-For materials that follow nonlinear elastic stress-strain behavior, the value of tangent or chord shear modulus is useful for estimating the change in torsional strain to corresponding stress for a specified stress or stress-range, respectively. Such determinations are, however, outside the scope of this standard. (See for example Ref (1).)³

The procedural steps and precision of the apparatus and the test specimens should be appropriate to the shape and the material type, since the method applies to a wide variety of materials and sizes.

Precise determination of shear modulus depends on the numerous variables that may affect such determinations.

5.3.1 These factors include characteristics of the specimen such as residual stress, concentricity, wall thickness in the case of tubes, deviation from nominal value, previous strain history and specimen dimension.

5.3.2 Testing conditions that influence the results include: axial position of the specimen, temperature and temperature variations, and maintenance of the apparatus.

5.3.3 Interpretation of data also influences results.