The behavior of Lamb waves in stressed polymer foils

The influence of externally applied unidirectional stress on the lowest-order Lamb modes of a 12-mu m poly(ethylene terephthalate) (PET) film has been investigated both theoretically and experimentally. The Lamb wave dispersion was determined in a fully contactless way by using optical generation and detection of ultrasound. The elastic parameters of the film material were obtained by fitting the angle dependence of the low-frequency Limit of the velocity of the fundamental Lamb modes. Whereas the dispersion of the symmetric mode S-0 is only slightly influenced by an external stress, the antisymmetric mode A(0) shows a transition from dispersion behavior determined by the elastic constants at small stresses to a behavior dominated by the applied stress at large stresses. (C) 1996 Acoustical Society of America.