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.
Experimental study of electromagnetic emission signals generated by crack generation in composite materials
The formation of a crack is accompanied by the generation of an electromagnetic field. A differential equation was derived and solved to describe the transformation of the field parameters into an electric signal, provided capacitive sensors are used. In the next stage, an analysis of spurious external electromagnetic and acoustic fields was carried out, and measures to suppress their effects were designed. The issue of amplifying extremely low electromagnetic signals generated during the crack formation was dealt with, too. The mentioned analyses resulted in the design of a method to detect and evaluate electromagnetic emission (EME) signals and acoustic emission (AE) signals, which accompany mechanical stressing of materials and structures. Based on the results of such analyses, an automated double-channel measuring apparatus was used for signal data acquisition, saving and processing. The operation of the apparatus was successfully tested by processing a large set of measurement results obtained from a composite material called ‘extren’. Our experimental results confirmed the correctness of both the EME and AE measurement methods, and measuring apparatus design. Our measurement results make it possible to track the behaviour of cracks, localize them and evaluate some of their basic parameters.
Electromagnetic radiation associated with induced triaxial fracture in granite
A study has been made of the electromagnetic radiation (EMR) emitted during triaxial compression of granite. Changes in EMR activity with loading are shown to be strongly correlated with changes in Poisson’s ratio but not with Young’s modulus. §