Relation of Electromagnetic Emission and Crack Dynamics in Epoxy Resin Materials

Abstract

Electromagnetic emission (EME) testing and acoustic emission (AE) testing are applied to investigate the failure of a brittle, dielectric material under mechanical load. A setup for three point flexure tests comprising simultaneous monitoring of EME and AE was used to induce fracture of epoxy resin specimens. The influences of the orientation and the distance of the crack surface on the detectable EME signals are the subjects of investigation. As EME sensor a capacitive sensor was used. Tests with an artificial test source are carried out to characterize the system response of the sensor, the attached amplifier and acquisition cards as well as the included bandpass filters. We propose an EME source based on the surface charge density modelled at the position of the fracture plane. Results of finite element method modelling of the EME source are compared to experimental results and show very good agreement. The experimental results show a clear directional character of the emitted electromagnetic field and a strong dependence of the detected signals amplitude on sourcesensor distance. A significant influence of the measurement chain on the detected electromagnetic signals bandwidth was found. Furthermore it is shown that the electromagnetic signals consist of three contributions originating from different source mechanisms. These are attributed to the separation and

Finite Element Method Applied in Electromagnetic NDTE: A Review

“…Finite element simulation of the wave phenomena typically requires a mesh density of order of λ/10, so Angstrom-scale of Roentgen rays make reliable 3D calculations impossible for even most powerful computers available at present. However, waves of higher length (including microwaves) can successfully be simulated, which was demonstrated in some papers [105][106][107].…”

“…In case of a crack initiation and propagation, a temporary electric charge imbalance is a source of an electromagnetic wave measurable within a distance of a few millimetres [106].…”

“…Gade et al [106] applied COMSOL commercial software to study the main characteristics of an EME sensor and obtained a very good correlation between the experiment and modelling. They claimed, that during the crack growth, an electromagnetic wave of acoustic frequency could be detected within a few mm from the surface of the studied epoxy resin object, and that EME could be a useful complementary tool for classic AE NDT.…”

“…-simulation not referred to any experiment [56,104] -qualitative correlation with an experiment [74,75] -relative quantitative correlation [106,117] -absolute quantitative correlation [97,113] Relative quantitative correlation is defined here as demonstrating the same per cent variation of modelled and measured signals, with differing baseline values, typical for 2D modelling. Often it is not possible to make a sharp distinction between relative and absolute correlation, as in [106], where the measurement is presented in terms of voltage, which naturally is influenced by tunable amplification factor.…”

“…Often it is not possible to make a sharp distinction between relative and absolute correlation, as in [106], where the measurement is presented in terms of voltage, which naturally is influenced by tunable amplification factor. If no reference to an experiment is provided, the paper should clearly demonstrate the soundness of modelling assumptions, and ideally be succeeded by another, experimental work.…”