Xiucheng Liu

Observation of ultrasonic guided wave propagation behaviours in pre-stressed multi-wire structures

HIGHLIGHTSTensile force measurement based on missing frequency band of ultrasonic guided wave in strands.Missing frequency bands of ultrasonic guided waves in tensioned steel wire ropes.Effects of tensile load on the ultrasonic guided wave energy attenuation in steel wire ropes.Ultrasonic guided wave energy jump behaviour in tensioned steel wire ropes. ABSTRACT Ultrasonic guided wave (UGW) is a promising technique for nondestructive testing of pre‐stressed multi‐wire structures, such as steel strand and wire rope. The understanding of the propagation behaviours of UGW in these structures is a priority to applications. In the present study, first the properties of the UGW missing frequency band in the pre‐stressed seven‐wire steel strand is experimentally examined. The high correlation between the observed results and the previously published findings proves the feasibility of the magnetostrictive sensor (MsS) based testing method. The evolution of missing frequency band of UGW in slightly tensioned steel strand is discussed. Two calibration equations representing the relationship between the missing band parameters and the tensile force are given to derive a new tensile force measurement method, which is capable of measuring an incremental of stress of approximately 3 MPa. Second, the effects of tensile force on the UGW propagation behaviours in three types of complicated steel wire ropes are alternatively investigated based on the short time Fourier transform (STFT) results of the received direct transmission wave (DTW) signals. The observed inherent missing frequency band of the longitudinal mode UGW in the pre‐stressed steel wire rope and its shifting to a higher frequency range as the increases of the applied tensile force are reported for the first time. The influence of applied tensile force on the amplitude of the DTW signal and the unique UGW energy jump behaviour observed in a wire rope of 16.0 mm, 6 × Fi(29) + IWRC are also investigated, despite the fact that they cannot yet be explained.

Damage imaging in composite plate by using double-turn coil omnidirectional shear-horizontal wave magnetostrictive patch transducer array

A double-turn coil omnidirectional shear-horizontal wave magnetostrictive patch transducer (DC-OSH-MPT) array for imaging detection in composite plates is presented. DC-OSH-MPT parameters are optimized in order to make the transducer more suitable for imaging detection. Besides, the characteristic of the lowest shear-horizontal mode (SH0), which can be generated and received in all directions by DC-OSH-MPT bonded on composite plate, is beneficial for imaging. Due to anisotropic property of composite plates, the group velocity of SH0 mode in different azimuthal directions was experimentally measured in damage imaging. The location of simulated damage, which was a bonded circular cylinder, was estimated by DC-OSH-MPT array and ellipse imaging algorithm. The imaging results have demonstrated that DC-OSH-MPT can be considered as a spatially distributed array suitable for imaging detection in composite plates.

A Novel Integrated Sensor for Stress Measurement in Steel Strand Based on Elastomagnetic and Magnetostrictive Effect

The deteriorating state of steel strands can be assessed using information of its overall and local stress level. An integrated sensor, which is based on magnetostrictive and elastomagnetic effect, is proposed for stress measurement of seven-wire steel strands. This integrated sensor can alternatively measure the stress level of seven-wire steel strands through guided wave-based technique and elastomagnetic method. When it works as magnetostirctive sensor to generate longitudinal guided wave in strand, the missing frequency band occurred in received wave signal is investigated in a pre-tensioned strand. It is found that the missing band central frequency increases linearly as the value of natural logarithm of overall stress increases. The integrated sensor can be applied to measure local stress in a strand based on elastomagnetic effect. The output signal amplitude of the sensor has linear relationship with strand stress level and stress increment of less than 10 MPa can be identified. The characteristic functions for both local and overall stress measurement are pre-calibrated experimentally. The proposed integrated sensor has great potential for applications of steel strands stress measurement.

Multi-variable regression methods using modified Chebyshev polynomials of class 2

Abstract So far, many regression works have been implemented by using linear regression methods. Although more accurate predictions results could be obtained, polynomial regression is not used as much as compared to linear regression in real applications due to occurrence of coefficient explosion. To overcome this problem, two regression algorithms using Chebyshev polynomials of class 2 based on cascade regression and feature selection are proposed in this paper. In the experimental part, three separate experiments including function interpolation and real-case regression were conducted on three datasets to test the proposed algorithms. As shown by the experimental results, the proposed algorithms performed better than other regression methods in terms of both accuracy and processing time.

Characterisation of case depth in induction-hardened medium carbon steels based on magnetic minor hysteresis loop measurement technique

Abstract The magnetic hysteresis behaviours of ferromagnetic materials vary with the heat treatment-induced micro-structural changes. In the study, the minor hysteresis loop measurement technique was used to quantitatively characterise the case depth in two types of medium carbon steels. Firstly, high-frequency induction quenching was applied in rod samples to increase the volume fraction of hard martensite to the soft ferrite/pearlite (or sorbite) in the sample surface. In order to determine the effective and total case depth, a complementary error function was employed to fit the measured hardness-depth profiles of induction-hardened samples. The cluster of minor hysteresis loops together with the tangential magnetic field (TMF) were recorded from all the samples and the comparative study was conducted among three kinds of magnetic parameters, which were sensitive to the variation of case depth. Compared to the parameters extracted from an individual minor loop and the distortion factor of the TMF, the magnitude of three-order harmonic of TMF was more suitable to indicate the variation in case depth. Two new minor-loop coefficients were introduced by combining two magnetic parameters with cumulative statistics of the cluster of minor-loops. The experimental results showed that the two coefficients monotonically linearly varied with the case depth within the carefully selected magnetisation region.

Megahertz-range longitudinal guided wave excitation by a flexible magnetostrictive sensor for steel strand inspection

A new type of sensing coil for magnetostrictive sensor (MsS) is presented in this paper. The flexible printed meander coil (FPMC) can offer micron level dimensional accuracy for the structure parameters which link to the central frequency of the MsS. Thus, the actual central frequency of the FPMC-based MsS can precisely meet the expected value. The number of coil groups in the FPMC is optimised to maximise the excited and received energy of the megahertz-range longitudinal guided waves in the strand and its central rod. Meanwhile, the FPMC can be easily wrapped onto the twisted strand surface and also can be installed onto the central rod of the strand after being wrapped into multiple layers. With the proposed megahertz-range FPMC-based MsS, the rod/strand inspection system is potential to be applied for practical inspections, having higher axial inspection resolution and sensitivity to small defects.