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Investigation of the factors influencing magnetic flux leakage and magnetic Barkhausen noise

Wang, Yujue 2021. Investigation of the factors influencing magnetic flux leakage and magnetic Barkhausen noise. PhD Thesis, Cardiff University.
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Abstract

Magnetic Nondestructive methods, including Magnetic Flux Leakage (MFL) and Magnetic Barkhausen Noise (MBN), are widely used to evaluate the structural integrity, mechanical properties, and microstructures of ferromagnetic materials. The MFL method is commonly applied to nondestructively evaluate the damage in ferromagnetic materials due to its reliability, high efficiency, and cost-saving. The MBN method is applicable in nondestructive evaluation (NDE) of mechanical and material properties due to the high sensitivity of Barkhausen jumps to residual (or applied) stress and microstructure of ferromagnetic material. The recognized research and successful applications helped these methods to be feasible NDE tools. However, there are still several important factors that may have noticeable influences on the experimental results of these NDE methods and usually are ignored in applications. In this thesis, the effects of the factors of stress and temperature on the MFL method, as well as the influences of temperature and microstructure on the MBN method are analysed via analytical and numerical modelling. A new finite element model for evaluating the effect of stress on the MFL amplitude is proposed and validated in defective steel under various stresses. Moreover, the new models describing the direct effect of temperature and the combined effects of temperature and thermal stress on the MFL signals are presented. The direct and combined effects are verified in an environmental temperature range from -40℃ to 60℃ by experimental results of a single lamination steel and multilayer structure, respectively. A set of newly derived equations modelling the effect of temperature on the MBN signals are given. Both the direct effect of temperature and the combined effects of temperature and thermal stress are considered in these equations, which are further simplified to linear functions consistent with the measured results in an environmental temperature range from -40℃ to 40℃. Furthermore, the microstructure factors, including the microstructure induced anisotropy in non-oriented silicon steel and the metallographic phases changing with carbon content in steel, are theoretically and experimentally investigated, respectively. For the factor of anisotropy, a new model II describing the dependency of Barkhausen emission on the angle between measurement and rolling directions is proposed. It allows the deduction of a trigonometric function to evaluate the effect of directional anisotropy. The agreement of simulated and measured results of MBN signals indicates the feasibility of the presented model. In the investigation of the influence of carbon content in steel on MBN signals, an optimisation method for MBN pick-up coil is proposed, and a multifunctional measurement system is presented. The correlations of the MBN signals and hysteresis loops related to the carbon content in steel are experimentally observed. The method for the quantitative evaluation of the carbon content using MBN signals and hysteresis loops are discussed

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Non-destructive Evaluation, Magnetic Flux Leakage, Magnetic Barkhausen Noise, Stress, Temperature, Microstructure
Date of First Compliant Deposit: 25 October 2021
Last Modified: 25 Oct 2021 11:45
URI: https://orca.cardiff.ac.uk/id/eprint/145021

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