Orthorhombic anisotropy: a physical model study

Scott P. Cheadle, R. James Brown, Donald C. Lawton

An industrial laminate has been shown to possess anisotropy when used as a medium for the propagation of elastic waves. The material, Phenolic CE, is composed of thin layers of canvas fabric with an approximately orthogonal weave of fibers bonded with a phenolic resin. Different compressional-wave velocities and distinct patterns of shear-wave splitting are observed in experiments involving ultrasonic transmission in three mutually orthogonal (principal) directions through a cube of the material, as well as between edges of the cube beveled at 45 degrees to the adjacent principal axes. Analysis of the results demonstrates that the phenolic laminate is suitable for modeling media with anisotropy of orthorhombic symmetry. The P-wave anisotropy varies from 6.3% to 22.4% and the S-wave anisotropy from 3.5% to 9.6% between pairs of the three principal axes. Expressions are presented that relate the measured body-wave velocities to nine elastic coefficients that define the stiffness matrix for this case of orthorhombic symmetry.