Torsional waves in a viscoelastic layer

Abstract

The objectives of this study are first to examine experimentally the propagation of torsional waves in a viscoelastic material, and second to use these data to determine the complex shear modulus of the material. The viscoelastic material used in this study is neoprene rubber. A magnetic drive is used to generate a transient, one-cycle, torsional wave in a brass rod, and this wave is transmitted into a layer of neoprene rubber bonded to the rod. A fiber-optic laser Doppler vibrometer is used as a noncontact probe to measure the torsional wave transmitted through the neoprene layer. The experimental data are compared with predictions from a theoretical model [D. P. Thomas, Int. J. Eng. Sci. 6, 565–570 (1968)]. Also, the complex shear modulus is determined from a least-square fit of the theoretical model to the experimental data using the downhill Simplex method. Another application of torsional waves is to nondestructive testing of materials, particularly for testing the strength of adhesive bonds between layers. [Work supported by ONR.]