Elastic constants of fiber-reinforced composites: a fresh measurement approach

Composites reinforced with uniaxial fibers possess five independent elastic constants: C₁₁, C₃₃, C₄₄ , C₆₆, and C₁₃. Measurements on a single specimen along principal axes give all the C_ij except C₁₃. To get C₁₃, a new approach is proposed that requires measurements only along principal directions: <100>. The approach also avoids the thin-plate problem, where measuring C₂₂ and C₃₃ may be difficult. A pulse-echo method is used to measure C₁₁, C₄₄, and C₆₆, and a resonance (kilohertz-frequency) method is used to measure two elastic compliances: S₁₁ and S₃₃. S₄₄ and S₁₂ come from simple formulas containing C₄₄ and C ₆₆. S₁₃ comes from a relatively simple formula containing S₁₁, S₁₂, S₃₃, and C₁₁ . The approach is applied to a graphite-magnesium composite