Effects of Homogenization and Quasi-Isotropy Assumptions on Guided Wave-Based Nondestructive Testing Methods

Abstract

Past research on guided ultrasonic wave-based methods for nondestructive testing of composite materials often assumed quasi-isotropy of composite laminates. Addition- ally, the quasi-isotropic laminate is homogenized and effective material properties for the laminate, modeled as a single layer material, are employed in subsequent analytical, numerical or experimental studies. However, deviations from the intended layup cause a directional dependency of the propagation velocities, thus requiring the modeling of the entire laminate. This not only alters wave fronts but it may also lead to significant errors in time-of-flight analyses for longer propagation ranges. Hence, in this paper, a comprehensive numerical-experimental approach is taken to investigate the quasi-isotropy of composite laminates in the context of guided ultrasonic wave propagation. A combination of semi-analytical and analytical tools are used to determine the dispersion curves and the propagation characteristics for several composite plate structures. The methods are applied for quasi-isotropic laminate that can be homogenized as well as a general composite laminate. The results are validated through dispersion experiments, and implications for damage detection are highlighted.