| From a new perspective, focusing on the relationship between the magnetic properties and stress of ferromagnetic material, the stress NDT&E for steel structure are researched in the thesis. This problem includes as follows: basic principle and theory, magneto-mechanical coupling model, application method, key realizing technology and so on. The dissertation research on NDT&E theory and application based on magnetic-mechanical coupling effect for steel structure is a daring explorations, which compensate the lack that there haven't been application of magnetic NDT&E to test stress for steel structure in civil engineering in China. Compared with other non-destructive techniques, the magnetic NDT&E for steel structure is a new promising technique in the future. The summary is listed below:(1)According to the ferromagnetic basic theory, the basic principle of magnetic NDT E for steel structure is analyzed. Theoretical major analyzes the influence of stresses on movement and change modes of magnetic domains in ferromagnetic materials and points out that the main modes stress influence movement of domains is the movement of domain wall and rotation of magnetic torque of domain. So the magnetic characteristic will be changed, and magnetic hysteresis loops have different feature. It is key that how to solve the relationship between the magnetic properties of steel structure and stress, or how to deduce the constitutive relation.(2)The model for steel structure stress NDT&E is set up and a simply constitutive relation expression of magnetic-mechanical coupling effect according to much theory deduction and analysis is deduced in the paper. The formula reveals the function relationship between magnetic properties change and stress of steel structure & member under external force. The constitutive relation is foundation of theory for experiment research and can guide stress testing for practical steel structure.(3)In coupling situation, a coupling parameter is put forward, which thinks over magnetic-mechanical coupling effect. Based on experiment, an experience formula of the coupling parameter is gained by numerical regression analysis methods of orthogonal experiment calculation, which has important significance for revising the magnetic-mechanical coupling constitutive relation formula The stress has more influence than magnetic on the coupling parameter.(4)The magnetic-mechanical coupling experiment of Q235 steel rod in building structure is completed in the paper for the first time. Q235 steel is a ferromagnetic material and is most extensively used for structure engineering. But there is few research on the magnetic properties changes by applying external loads for this sort of low carbon steel. Experimental measurements of magnetization curve arepresented, and magnetic hysteresis loops have changes due to undergoing an external variable stress for Q235 Steel Rod. When in the stage of the level of magnetization saturation hasn't been arrived, the experimental results showed that the permeability under 0 stress is smaller than under tensile stress and bigger than the permeability under compressive stress. While magnetization arrived at the level of saturation, the permeability under 0 stress is bigger than both under tensile stress and under compressive stress. If the tensile stress increase, the permeability of Q235 steel rod tends to decrease, if the compressive stresses increase, the permeability of Q235 steel rod tends to increase. This mutual influence relation provides an experimental foundation for the magnetic NDT&E of steel structure later. The theory analysis of the simplified constitutive relation expression is an agreement with the experimental results of magnetic hysteresis according to the qualitative analysis. Both of them are mutually confirmed. From quantitative analysis and contrast, in different external magnetic situation, the experimental result figure of Q235 steel rod magnetic-mechanical constitutive relation is set up for the first time. A best numerical range of exciting magnetic is determined. The permeability is a function of both external magnetic and stress. According to experiment results, an experience formula of the permeability is gained by regression analysis methods of orthogonal experiment numerical calculation, in which calculation error is very small. The change of magnetic field has more influence than stress on the permeability. A three dimension figure of permeability-stress corresponding relation is gained according to the result of numerical calculation. If there were many times reference of experimental results, and the experience formula of the permeability-stress corresponding relation will be made a demarcate according to these data, then a more exact testing result will be obtained.(5) In different external magnetic situation and different stress situation, the H-B constitutive relation model have been gained by the theoretical constitutive relation expression formula of magnetic-mechanical coupling effect and by the coupling parameter that is revised by the experiment The H-B constitutive relation model is numerical calculation by the commercial finite element program ANSYS, which is attempts to simulate die increasing part of the H-B curve of Q235 steel which is in uniaxial stress stage. By setting up the runway coil, an external magnetic can be induction by the runway coils. When the coil's number is 8000, the induction external magnetic has included the best numerical range of measure external magnetic. The ANSYS numerical calculation results show that the H-B curve can be gained, and permeability-stress corresponding relation can be gained according to the result of numerical calculation. The change regularity of permeability influenced by stress can be reflected according to calculation results. According to the calculation analysis, the theory and experiment and ANSYS calculation are identical and are mutually confirmed. The numerical method by amending ANSYS program is available. The error is mainly corrected with the numerical of constitutive relationmodel. If the numerical value that is selected has more representation character, the calculation results are closer to real values.(6) How to measure magnetic is another key technology. Aim at magnetizing and measure magnetic, several concretized suggest that can be suitable for testing stress of building steel structure are posed according to section shape of steel structure member, which is Hie basement of how to develop testing equipments by magnetic-mechanical coupling for steel structure.(7)Several key technologies that how to realize stress NDT&E by magnetic-mechanical coupling for steel structure are discussed, and the accuracy of stress testing result is very depended on the magnetizing and magnetic signal measure and processing. A initial route of how to realize stress testing technology is put forward, whose most key problem is how to measure the value of magnetic characteristic parameter of steel structure member under coupling influenced by stress and magnetic. The magnetizing technology is the first key step, whose key problem is to determine the best numerical range of measure external magnetic. Magnetic signal measurement is the second key step, which includes how to produce magnetic signal and how to measure magnetic signal, and the transformation of magnetic signal is core, in which the key problem is how to define the magnetic-mechanical coupling constitutive relation. The processing technology is the third key step, which includes how to magnify and filter magnetic signal and other key segment. The anti-inference and demagnetization technology are of necessity.
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