Characterization of Viscoelastic Unidirectional Composite Laminates using So, Ao and SHo Lamb Waves

This paper discusses the application of Lamb wave dispersion data for quantitative, material characterization of unidirectional composite laminates (carbon fiber/epoxy). The dispersion data of S-o, A(o) and SHo Lamb modes are obtained experimentally in the frequency range from 10 kHz to 500 kHz by using surface-bonded thin Piezoelectric Waver Active Sensors (PWAS) by a pitch-catch approach. Through a detailed parameter and sensitivity study it is shown that most of the stiffness coefficients (real and imaginary parts) can be determined through an inversion scheme. The real part can be obtained by inverting the velocity dispersion data, the imaginary part (for viscoelastic material behavior) from the attenuation dispersion curves. For data inversion a simplex optimization algorithm was used combined with an analytical model for viscoelastic Lamb wave propagation. The wave propagation model is based on a higher order plate theory and a hysteretic material damping model, as developed in [1] and briefly presented in [2].