ROTATION OF ELASTIC SHEAR-WAVES IN LAMINATED, STRUCTURALLY CHIRAL COMPOSITES

We present experimental and theoretical data to support the hypothesis that elastic shear waves can sense the microstructural handedness, if any, in a material. Structurally chiral composites are constructed by stacking identical uniaxial plates, their symmetry axes describing either a left- or a right-handed spiral. Four glass-reinforced laminated composites-left- and right-handed, pure uniaxial and random-were made to verify the effect of form or structural chirality on elastic shear wave propagation. The composites were characterized by using shear wave transducers in an ultrasonic through-transmission experiment. Test results indicate that shear waves transmitted through left- and right-handed chiral composites have polarization states that are rotated clockwise (CW) or counter-clockwise (CCW) with respect to the incident linearly polarized wave. The uniaxial sample and the random sample did not show this effect. This effect is similar to the rotation of the plane of polarization of electromagnetic waves in "optically" (electromagnetically) active media. Wave propagation in the samples was also analyzed numerically using a matrix representation method. The experimental data compares with the numerical results qualitatively. © 1992.