| Because of welding, casting and long service, the stress exists in ferromagnetic components, which can do great influence to the mechanic properties of ferromagnetic components. In the process of welding, the welding stress will be generated; Ferromagnetic components will generate the impact stress after applying the shock load and the thermal expansion and cold shrinkage. The most obvious examples are continuous welded rail (CWR), the huge vertical thermal stress generated in the long rail, and the weld structural stress of ship steel plate.According to metal magnetic memory (MMM) and magnetic Barkhausen noise (MBN) theory, the advantages of MMM and MBN techniques are fused and the possible application of MMM-MBN fusion online testing method is explored to solve the scientific and technical problem of non-destructive and quick online stress testing. From the results, we can get the following conclusions:1. The average volume of magnetic Barkhausen jump (AVMBJ) generated by magnetic domain wall irreversible displacement under the effect of the incentive magnetic field for ferromagnetic materials and the relationship between irreversible magnetic susceptibility and stress are adopted in this paper to study the theoretical relationship among AVMBJ and the incentive magnetic field. Then the numerical relationship among AVMBJ, stress and the incentive magnetic field is deduced. Utilizing this numerical relationship, the displacement process of magnetic domain wall for single crystal is analyzed and the effect of the incentive magnetic field and the stress on the AVMBJ is explained from experimental and theoretical perspectives. The saturation velocity of Barkhausen jump characteristic value curve is different when tensile or compressive stress is applied on ferromagnetic materials, because the resistance of magnetic domain wall displacement is different. The idea of critical magnetic field in the process of magnetic domain wall displacement is introduced in this paper, which solves the supersaturated calibration problem of calibration curve.2. According to MMM and MBN theory, we designed and constructed the specialized sensors to detect thermal stress. Moreover, corresponding drive circuit, amplifying circuit and data collection circuit are designed. A friendly user interface can be realized by a high-performance ARM processor and the MMM and MBN work system can be automatically switched by automatic regulation technique.3. MMM and MBN theory and method are researched. For the requirements of wide range and real-time stress testing, the advantages of MMM and MBN techniques are fused and the possible application of MMM-MBN fusion online testing method is explored herein, which can greatly improve the detection efficiency and accuracy in stress detection:(1) The stress distribution of E36 and CCSB grade steel plate is detected and analyzed. The weld structural stress of E36 grade steel plate test chamber before and after explosion and impact are compared. The weld structural stress of CCSB grade steel plate test bench was detected before and after impact.(2) The dam stability model and the dam stability formula of the CWR have been established. It based on the strength and stability of CWR, the virtual work principle of static equilibrium was adopted to establish the compressive thermal stress formula of CWR. This formula can calculate the current stored energy of the CWR, and indicate the stability of CWR from the perspective of energy.(3) A new method is proposed on the basis of finite element analysis and discrete short time Fourier transform methods to evaluate the global and local stability of CWR. The local stability evaluation criterion and the global standard deviation of thermal stress fluctuation of CWR are proposed.(4) The actual stress free temperature formula of CWR and its online detection and implementation methods were established based on the online thermal stress and the on-site rail temperature of CWR. |
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