Experimental aspects of quantitative nondestructive evaluation using guided waves

For successful experiments with guided waves for quantitative nondestructive evaluation, e.g. the determination of complex material properties, a number of elements are crucial. Very often, a frequency range far below 1 MHz is employed. Therefore, if piezoelectric transducers are used, they are excited far below their first resonance frequency. Low frequency models for the excitation of longitudinal and bending waves including shear effects are therefore presented in the first part of this paper. In order to make contactless measurements, it is advantageous to use laser interferometry. A special high resolution phase demodulator for the frequency range from 1 kHz to 8 MHz is described. A total least squares algorithm is used to deal with multiple modes of propagation. It allows us to determine experimentally the dispersion curves to be used for the calculation of complex material properties. As a special case, axisymmetric wave propagation in transversely isotropic composite bars is used to characterise fully the elastic properties of the material.