Shear-Modulus Determination of Isotropic and Composite Materials

A new test technique that uses split rings to determine the shear modulus of isotropic and composite materials is described. In this test, two concentrated loads that are equal in magnitude but opposite in direction and act normal to the plane of the ring are applied at the point where the ring is split. Pertinent equations which relate the resultant ring deformation to the physical and mechanical properties are given. The out-of-plane deflection is predominantly due to shear deformation, which makes this test an ideal one for shear-modulus determination. Tests are conducted on steel and aluminum rings to demonstrate the accuracy of the new test method. The measured shear moduli are shown to agree within 2 percent of the values reported in the literature. The test then is used to measure the shear moduli of epoxy resin, unidirectional fiber glass composites, bidirectional fiber glass composites, unidirectional boron-epoxy composites, and unidirectional Thornel 40-epoxy composites. The experimental results are compared with theoretically predicted values, and a good agreement is found. Finally, a discussion of existing test method's for shear determination is presented, and the shear moduli obtained by various tests are compared.