engleski

Modeling of pulsed eddy-current measurement of hard carbide layer thickness

Hard carbide layers are formed on the surface of steel structural elements to increase their resistance to tribological wear. Thickness of the hard carbide layer has to be monitored in production as well as during the exploitation of the steel element. Various NDT methods can be applied for measurement. Pulsed eddy-currents (PEC) are particularly interesting because of their broad frequency content and potential information about steel bulk material and hard layer thickness from a single measurement. We present mathemati-cal modeling of pulsed eddy-current inspection of a two-layer structure. We investigate features of the PEC response applicable to measurement of the hard layer thickness. We have derived analytical expressions in frequency domain for generation of eddy currents in a two-layer planar geometry. Sys-tem is described in time domain by application of the inverse discrete Fou-rier transform. The model can be used for various pulsed excitations. Both layers in the model can have arbitrary electrical conductivity and magnetic permeability. The model is applied to a structure consisted of a ferromag-netic steel element with thin layer of vanadium-carbide. The results confirm applicability of pulsed eddy currents to measurement of the hard layer thick-ness and point towards the optimal processing of the PEC response

hard carbide layer; steel; thickness measurement; pulsed eddy currents; mathematical modeling

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