Lamb wave characterization of the effects of long-term thermal-mechanical aging on composite stiffness

Abstract

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.

Ultrasonic guided waves for health monitoring of high-pressure composite tanks

“…The inverse routine based on Lamb mode measurements [13] mentioned above allowed showing that this general increase in the wave-numbers, between the initial state and the last immersion at À196 1C, corresponds to a decrease of about 15% of all the elastic moduli C 0 ij . This confirms previous studies, which have shown that very low temperatures cause damages to composite materials, which can be monitored using Lamb waves [3,14,15]. A nominal 20% decrease in the C 0 ij will be used further as an input data to the Surface impedance model to simulate micro-cracking in the carbon winding, and to predict its effect on the propagation of modes guided along the tank.…”

“…Air-coupled transducers can provide solutions to these demands, and they also guarantee very reproducible measurements, hence being good candidates for replacing traditional contact transducers coupled with gel [2]. In this paper, air-coupled ultrasonic transducers are used for generating-detecting Lamb waves and for measuring their characteristics, such as wave-numbers and attenuations, which have previously been shown to be good indicators of either microcracking or moisture content, respectively, in carbon-epoxy plates [3][4][5]. A wave propagation model based on the Surface impedance matrices method [6] is also employed in an inverse scheme to quantify the effects of moisture content or of micro-cracking on the material properties (complex moduli of viscoelasticity) of carbon-epoxy plate samples.…”

Ultrasonic Guided Waves for Health Monitoring of High Pressure Composite Tanks

“…Air-coupled transducers may provide solutions to these demands, and since they also guarantee very reproducible measurements, they are good candidates for replacing traditional contact transducers coupled with gel. In this paper, some correlations between complex moduli of viscoelasticity and micro-cracking [2,3] or moisture content [4] in Carbon epoxy plates are firstly reminded. Probable changes in Carbon epoxy properties are then used as input data in a wave propagation model based on the Surface impedance matrices method [5], for predicting the behaviour of wave modes guided in a high-pressure composite tank made of a Titanium liner with Carbon fibres wound around it.…”

Air-coupled guided waves combined with thermography for monitoring fatigue in biaxially loaded composite tubes

“…They offer a convenient method for recovering inplane elastic properties [6,7]. Contact Lamb wave setups were found to be applicable to monitoring stiffness degradation in FRP induced by thermal and mechanical ageing [8][9][10]. It was shown that the attenuation is sensitive to cracking induced by fatigue for a circumferential wave propagating in hollow FRP cylinders [11].…”