Lamb waves from microfractures in composite plates

The relationship between the signatures of the surface responses and the characteristics of microfractures in the plates is studied here to establish the theoretical background for acoustic waveform analysis and non-destructive monitoring of the damage evolution in composite plates. Lamb waves produced by internal sources in transversely anisotropic plates and laminated composite plates are investigated in an effort to understand the evolution of the disturbance.; Three-dimensional elasticity theory is used to formulate the wave propagation problem in transversely anisotropic plates using the integral transform technique. The displacement in the far field is obtained in terms of propagating symmetric and antisymmetric Lamb wave modes by using the method of stationary phase.; Laminate theory with shear correction is used to model wave motion in thin composite plates with a general lay-up of the laminae. The three-dimensional equations of motion are reduced to two-dimensions by applying integral operators and the resulting equations are solved. The relationship between the excitation of different modes and the distribution of the internal source is discussed.; Based on the theory developed, the surface responses of a composite plate due to different microfracture sources are calculated. Finally, laboratory experiments are performed to validate the theoretical models. Good agreement between the experimental measurements and theoretical calculations is achieved in all cases considered.; The results of this research should be useful in developing practical nondestructive tools to monitor damage evolution in composite structures.