Experimental study of electromagnetic emission signals generated by crack generation in composite materials

Abstract

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.

Relation of Electromagnetic Emission and Crack Dynamics in Epoxy Resin Materials

“…10) one has to take into account that the AE frequencies are influenced by the geometry of the specimen and the propagation path from the source to the acoustic sensor [8,42]. Furthermore, only the propagation of the crack tip and the vibration of the crack surfaces contribute to the EME and the AE signal while the charge relaxation only contributes to the EME signal.…”

“…The occurrence of this electromagnetic emission (EME) has been shown for almost any material and for various kinds of failure mechanisms [1][2][3][4][5][6][7][8][9]. The detection and analysis of EME can help to understand the complex processes of crack formation.…”

“…According to [8] the detectable signals are a function of the orientation of the crack surfaces relative to the sensor. Furthermore, the signals may contain information about the spatial and temporal characteristics of their sources [2].…”

Measurement and Study of Electromagnetic Emission Generated by Tensile Fracture of Polymers and Carbon Fibres

“…However, a consistent model for the description of all experimental results concerning EME has yet to be proposed. Most theories presume the dynamics of charges connected to the dynamics of the fracture process to be the source of EME [12,14,15]. Some authors have pointed to the charge separation or electrification of the crack surfaces to be an important source process [6,16,17].…”

Study of the Development of Cracks Accompanying Mechanical Loading of Solids

“…The phenomenon of electromagnetic emission (EME) from solids (Koktavý, 2009) is based on the generation of an electromagnetic field arising from the mechanical excitation of the solid in question. This phenomenon may be triggered, for example, by external pressure, tensile, bending, shearing force, shocks, drilling, scratching, crushing, material fibre cutting, etc.…”