MATERIAL CHARACTERIZATION BY PULSED EDDY CURRENT M.Zergoug,N.Boucherrou
Centre de Recherche Scientifique et Technique en Soudage et Contrôle, Route de Dely Ibrahim, B.P. 64, Chéraga, Alger, Algérie
Tél. & Fax : (213) (21) 36 18 50
ABSTRACT: The Pulsed eddy current (PEC) application in the industrial domain is very weak compared to conventional eddy current. Its use in detection of the defects, particularly in the determination of corrosions .The contained information in the received signal makes it possible to determine several parameters with an aim of analyzing material. The results obtained explain the behaviour of the Pulsed Eddy Currents and their influences in various electromagnetic parameters on the inspection. We will evaluate the aptitudes and the performances of this technique in the determination of the characteristics materials in particular. Also we have studied the sensitivity of the defects and other parameters in the inspection by the pulsed method and we have showed the detection of the defects into the second and third layers. The originality of this work consists of the material evaluation. The applied NDT PEC methods can characterize microstructure types, micro structural changes, hardness changes. The objective of our work is to evaluate some metallurgic characteristics by non-destructive methods. The characterization of the structure modifications by PEC allows to detect mechanical and metallurgical parameters of materials
INTRODUCTION
The development of non-destructive testing has a considerable importance. Pulsed eddy current measurements is very used in the non destructive testing such the detection of defects, corrosion[1]. In the transient eddy-current method an eddy-current pulse is generated at the surface of a structure and propagates down into the structure over the course of a few milliseconds. The magnetic field measured at the surface will be modified by any changes in the propagation path of the pulse, such as caused by defects, conductivity changes, edges or interfaces. The eddy-current pulse contains a broad frequency spectrum, which is of great benefit during analysis of the signals.
The signal obtained during PEC (figure 1) give material information’s. The amplitude
analysis can give us information on a possible micro structural change or the presence of a
defect. In order to improve PEC testing can be done by the use of signal processing as Fourier transformer. The signal obtained presents three important parameters, the amplitude of the
first peak and the second peak and the de phasing which can be obtained during the control of the structures into multi-layer or in the presence of various defects[2]. Crack Detection and
Characterisation:
PHYSICAL APPROACH
With conventional eddy current systems the coil is continuously driven with a sinusoidal
waveform. With a transient (or ‘pulsed’) eddy current system the drive coil is energised with a periodically reversing current (essentially a controlled rise-time square wave). This field
reversal causes a ‘pulse’ of eddy currents that propagate down into the structure. A field
