Monitoring of the moisture content in carbon-epoxy plates using Lamb waves

Theoretical and Experimental Investigations of Transmission Coefficients of Longitudinal Waves through Metal Plates Immersed in Air for Uses of Air Coupled Ultrasounds

“…So many applications for the Lamb wave transductions using the airborne ultrasounds were reported. Acoustic anisotropy measurements of various kinds of thin plates, 11) lap-joint qualities of adhesive aluminum plates, 12) plate thickness measurements using the Lamb wave dispersion-relations, 13) moisture-content estimations in polymer materials using the attenuation factors of the A 0 -mode Lamb waves, 14) thickness measurements of Al plates 15) and delamination detections in CFRP plates 16) were, respectively, carried out. Very interesting way to use the zero group velocity (but finite phase velocity) region of the S 1 -mode Lamb wave was proposed for efficient defect detection in plates.…”

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

“…It is of importance to note that such possible changes in the attenuations of these A 0 -like modes are just slightly higher than the accuracy of attenuation measurements made with the technique described in Ref. [5]. This technique consists in launching one mode with an air-coupled transmitter, in moving an air-coupled receiver over a distance equal to a couple of wavelengths (E5 cm) along the propagation path of the mode and in processing two spatial FFT's from two sets of signals measured along two monitoring lines dividing equally the total displacement of the receiver.…”

“…Then a drying process consisting of placing the sample in a dry oven at 65 1C for 2 months is performed. The wave-numbers and attenuations of the three Lamb waves A 0 , S 0 and S 1 are measured at several steps during the whole ageing-drying process, using the air-coupled system, in the frequency range 100-350 kHz [4,5]. Changes in the plate weight are also monitored to have another control of the moisture content.…”

“…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.…”

Efeito higrotérmico em prepregs de fibra de vidro/epóxi por espectroscopia de luminescência

“…Na interface fibra-matriz, a água pode formar ligações hidrogênio com grupos funcionais contendo oxigênio da fibra de vidro, o que pode reduzir a adesão entre a fibra de vidro e a resina epoxídica. Um outro efeito causado pela ação da água é o preenchimento de micro-cavidades da matriz por moléculas de água, gerando micro-fissuras nas interfaces fibra-matriz [3][4][5] . A influência da água nas propriedades de compósitos tem sido largamente estudada por meio da utilização de técnicas tais como espectrometria de absorção na região do infravermelho (FT-IR) [6,7] e espectroscopia de tempo de vida de aniquilação de pósitrons [8,9] , além da avaliação das propriedades mecânicas e térmicas [10][11][12] .…”