Liu Xiucheng

Megahertz-range magnetostrictive sensor for exciting longitudinal guided waves in steel rods/strands

A flexible printed meander coil (FPMC)-based magnetostrictive sensor (MsS) which has a central frequency around 1.25 MHz is presented in this paper. The FPMC-based MsS can be easily wrapped onto the twisted strand surface and disassembled from the strand. It can be also installed onto the central rod of the strand after being wrapped into multiple layers. That is, this FPMC-based MsS can fit for the tested sample of different diameters. With the proposed megahertz-range FPMC-based MsS, the rods/strands inspection system is potential to be applied for practical inspections, having higher axial inspection resolution and sensitivity to small defects.

Characterization of Elastic and Plastic Behaviors in Steel Plate Based on Eddy Current Technique Using a Portable Impedance Analyzer

A portable impedance analyzer (PIA) was developed based on a TiePie-HS3 device to provide the comparable impedance measurement accuracy of the Agilent 4294a impedance analyzer in the frequency range of 0~250 kHz. Then the PIA was applied to monitor the tensile stress-induced variation of the eddy current sensor’s impedance in a medium-carbon steel sample. A model of equivalent magnetic field induced by the elastic stress and the number of pinning sites indicated that the inductance of the eddy current loop firstly increased with the increase in the tensile stress and then decreased at the yield point of the material. The experimental results testified that the variation of impedance amplitude, the variation of phase angle, and the shift of two featured frequencies demonstrated opposite variation trends before and after the yield point, as predicated by the model. A new parameter, which combined the impedance variation information of the selected two frequencies, was found to exhibit nearly monotonous dependency on the tensile stress in elastic and plastic stages. The new parameter together with the developed portable impedance analyzer provided the solution to identify the elastic and plastic behaviors in ferromagnetic materials in practical applications with an eddy current technique.