Determination of the orthotropic elastic constants of thin PET film by an ultrasonic micro-spectrometer

The elastic constants of a thin polyethylene terephthalate (PET) film, whos e thickness was 12 mu m, were determined from the acoustic reflection coeff icients. The reflection coefficients were measured by an ultrasonic micro-s prectrometer (UMSM), and all of the elastic constants were obtained through the fitting of a theory to the dip points of the magnitude of the reflecti on constants where leaky Lamb waves were excited. As a result, the film was found to be an orthotropic material, and the observed elastic constants we re consistent with those measured by tensile tests. Besides, the in-plane s hear modulus was found to be much larger than the out-of-plane shear moduli . Then, the reflection coefficients were calculated using the obtained stif fness matrix. The calculated values reproduced not only the dip points but also the change in magnitude of measured reflection coefficients depending on the frequency and the incident angle. These agreements suggest that the stiffness matrix components were determined accurately.