A complete mechanical-property characterization of a single composite specimen

For a unidirectional lamina, the in-plane mechanical properties of interest areE ₁₁,E ₂₂, ν₁₂, ν₁₂ andG ₁₂. Only three of the first four listed are independent. The fourth may be calculated from the reciprocal relationshipE ₁₁ ν₂₁ =E ₂₂ ν₁₂, which results from stiffness-tensor symmetry. Measurement of any four of the five properties listed will completely characterize the in-plane mechanical properties. A longitudinal uniaxial tension test was used to evaluate longitudinal modulus and Poisson's ratio. A modified rail-shear apparatus was designed to measure shear modulus in a rail-shear orientation, as well as a totally constrained transverse modulus in a uniaxial tension test with an orientation transverse to the longest dimension of the specimen. A flexure test was also used to estimate transverse moduli, since the achievement of the totally constrained transverse-modulus measurement was impaired by the variability of load distribution and constraint across the breadth (10-in. length) of the specimen. An apparatus was designed that applied a line loading to the specimen, simply supported on two opposite sides, with the two remaining sides free. The feasibility of this technique was documented by comparing measured values of the transverse modulus and out-of-plane displacement for a 0°]₄ specimen to values obtained from the Levy solution for bending of an orthotropic plate.