Lamb waves offer a promising method of evaluating damage in composite materials. The Lamb wave velocity is directly related to the material parameters, so an effective tool exists to monitor damage in composites by measuring the velocity of these waves. The Lamb Wave Imager (LWI) uses a pulse/receive technique that excites an antisymmetric Lamb mode and measures the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. In this study, the time-of-flight as well as the elastic stiffnesses D11, D22, A44, and A55 for composite samples which have undergone combined thermal and mechanical aging are obtained. The samples examined include a baseline specimen with 0 cycles, specimens which have been aged 2350 and 3530 cycles at high strain levels, and one specimen aged 3530 cycles at low strain levels.

Lamb wave methods offer a promising approach for evaluating damage in composite materials. The Lamb wave velocity is directly related to the material parameters, so an effective tool exists to monitor damage in composites by measuring the velocity of these waves. In this work, studies have been conducted which examine the effects of combined thermal and mechanical aging in thermoplastic composite samples using symmetric mode Lamb wave velocity measurements. From the velocity measurements, the in-plane stiffnesses, A11 and A22, are calculated. The samples examined include a baseline specimen with 0 hours, specimens which have been aged 3,500 and 5,000 hours, and one specimen with 1,000 hours of accelerated aging. The results of the Lamb wave measurements are compared to C-scans of the panels.

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Among the various techniques available, ultrasonic Lamb waves offer a convenient method of examining composite materials. Since the Lamb wave velocity depends on the elastic properties of a material, an effective tool exists to evaluate composites by measuring the velocity of these waves. Lamb waves can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper discusses a study in which Lamb waves were used to examine fiber volume fraction variations of approximately 0.40-0.70 in composites. The Lamb wave measurements were compared to fiber volume fractions obtained from acid digestion tests. Additionally, a model to predict the fiber volume fraction from Lamb wave velocity values was evaluated.