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A new test technique for measuring the shear moduli of isotropic and composite materials is described. The test technique employs circular rings subjected to out-of-plane four-point loading: four forces of equal magnitude, two upward at 0 and 180 deg and two downward at 90 and 270 deg. The pertinent equation relating ring deformation to applied loading, ring-section properties, and elastic properties is given. It is shown that by selecting appropriate specimen geometry, the deflection of the ring subjected to four-point loading is governed primarily by shear deformations. The reliability and accuracy of the test method are demonstrated by conducting tests on metallic rings as well as on rings made of various composite materials. Room as well as elevated-temperature shear-moduli data are measured using the ring tests. The results from the four-point ring-twist tests are compared with data presented in the literature. The test is simple and fast, with no requirement for elaborate instrumentation or setup. Moreover, the test is applicable for measuring the shear moduli at room temperature, cryogenic temperatures, and elevated temperatures.
composite materials, testing, shear modulus, ring tests, elevated temperature
McDonnell Douglas Astronautics Co., Huntington Beach, Calif.