Ultrasonic Elastic Constants of Carbon Fibers and Their Composites

The elastic constants of carbon-fiber-reinforced composites have been measured with an ultrasonic immersion technique. Both carbon and graphite fibers were studied. These fibers were derived from both rayon and polyacrylonitrile (PAN), and had Young's moduli ranging from 6 to 80×106 psi. The composite elastic constants varied with fiber modulus and fiber type (carbon or graphite) but not with the fiber-matrix bond. The fiber elastic constants c11 and c66, corrected for porosity, varied with fiber modulus but not with fiber type. The fiber constants c44 and c13 were independent of fiber modulus but varied with fiber type.