Off- Diagonal Elastic Constants in Fiber-Reinforced Composites
H M. Ledbetter, C M. Fortunko, Paul R. Heyliger
We present an alternative to the usual rod-resonance and pulse-echo measurement methods for determining off-diagonal Cij. The new approach - acoustic resonance spectroscopy (ARS) - avoids the above problems by treating, for example, C12 the same as C11. Among numerous advantages, ARS offers the principal advantage of one measurement rather than nine or more. The method proceeds from the premise that we can calculate the macroscopic vibration frequencies Fi of a simple-shape solid (sphere, cube, disc, parallelepiped, and so on) from four ingredients: shape, size, mass, and elastic constants. Thus, we can determine the elastic constants by measuring the Fi and doing an inverse calculation for the Cij. Here, we consider two uniaxial-fiber-reinforced aluminum-matrix composites: 48-vol% boron fibers, 70-vol% graphite fibers.