DETERMINATION OF ELASTIC-MODULI IN ANISOTROPIC MEDIA FROM ULTRASONIC CONTACT MEASUREMENTS

When laminae are smaller than the wavelengths that measure them, a com posite appears homogeneous and anisotropic. Composites are often subje cted to high temperature gradients during their fabrication which can result in residual stresses, and damage in the form of oriented microc racking may result. Oriented microcracks will render a normally isotro pic material anisotropic. Similarly, the resultant of a cracked anisot ropic composite is a complex combination of the two component anisotro pies. This work attempts to separate experimentally the anisotropic ef fects of vertically oriented microcracks from a background that is alr eady anisotropic. A physical model was constructed in which vertical f racturing was superposed on a transversely isotropic material. The fin al specimen displayed orthorhombic symmetry. Laboratory measurements w ere made at ultrasonic frequencies to determine the elastic moduli of this material. From these moduli, the elastic properties of the origin al background, as if it had no vertical cracks, were determined as wel l as the additional compliance that the cracks add to the system.