In this paper, according to the disperse curve of composite laminates in a low frequency domain, a quantitative relation between anisotropic wavefront and propagation direction is proposed to reveal the direction dependency of Lamb wave propagation in composite laminates. This relation is described by a concise analytic expression, which can effectively incorporate anisotropic wave propagation into damage identification and reasonably determine the time-of-flight (ToF) of the Lamb wave. The reliability and applicability of this quantitative relation are validated by numerical simulations and experiments in three different lay-up composite laminates. Furthermore, combining this quantitative relation and the conventional ToF approach, an effective detection method is developed for damage localization in composite plate-like structures. By using PZT sensors, the method is conducted experimentally in a cross-ply laminate. The Gabor wavelet transform is introduced for signal processing to identify the ToF more exactly. Results indicate that a satisfied damage location can be achieved by considering the orientation dependency of anisotropic wave propagation in composite laminates.

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The effect of loading rate on the dynamic fracture properties and the failure mechanisms of glass fiber-reinforced composite materials under mode I fracture is studied. Dynamic reflective caustic experiments are carried out for two loading rates. By measuring the characteristic dimensions of the shadow spots during the caustic experiments, the dynamic SIFs are calculated for different loading rates. The experimental results indicate that the dynamic fracture toughness K Id increases remarkably with increasing loading rate, and the crack grows faster under the high-velocity impact. Moreover, by examining the crack growth routes and the fracture surfaces, it is shown that the loading rate also greatly affects the failure mechanisms at micro-scale.

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