Noise diagnostics of advanced composite materials for structural applications
Our study is focused on noise diagnostics of an advanced composite material for structural applications called extren, which consists of a combination of a fibre glass reinforcement and a resin binder. Electromagnetic and acoustic emission signals appear during mechanical loading of the material under investigation. They carry information about micro-cracks generated in tested materials. We made long-time simultaneous multi-channel measurements of both signals for various loading conditions, carried out time development of noise spectrum, evaluated parameters of EME and AE events, studied their time development, correlations between them and made statistical analyses of signals and their parameters.
Statistical characteristics of electromagnetic emission signals of mechanical loaded composite samples
1 Department of Physics, Faculty of Electrical Engineering and Communication, BUT, Technická 10, 616 00 Brno E-mail: xpodsh00@stud.feec.vutbr.cz Abstract: This article presents study of statistical characteristics of EME signals. The theoretical part contains a description of stochastic nature of electromagnetic emission. We describe the measuring system, the sequence of the experiment, statistical characteristics (probability density function, mean quantity and dispersion) and spectral analysis (voltage and current power spectral density of measured EME signals). In the practical part of the article we also have compared results obtained on the basis of experiment with theory.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.