Stress Detecting Technology Research Of Construction Steel Materials Based On Magnetic Coupling

It is demanded for millions and millions tons of construction steel material eachyear with continuous improvement of technology and social economic power. As themain structural steel components, they are often responsible for a huge load. Therefore,the direct detection method of the actual building steel stress state has become animportant research topic in the contemporary field of structural health diagnosis. Theresearch achievement has great value in engineering and is bound to promote the overallanalysis level of the structural safety evaluation.In this paper, the domestic and foreign common detection methods based onferromagnetic materials are summarized, and focused on the stress detection technologyof structural steel material based on the magnetic coupling. And as the background forthe study, the basic theory and application methods is researched systematically throughtheoretical analysis, experimental and model simulation techniques, the main researchwork are as follows:(1) According to the composition of construction steel materials, the basic principleof stress and impurity impacting on magnetic domain and domain wall are researchedcombined with the theory of ferromagnetic. The analysis shows that the stress makes thecrystal stress energy increasing and the magnetization direction changing with the stressdirection. The impact of impurities on the magnetic domain is very complex so weshould verify the influencing range to the through a large number of tests. The generalrules of detecting steel stress is elaborated by technical magnetization, and whichprovides the necessary theoretical supports for establishing the theoretical model ofmagnetic coupling.(2) Through Joule inverse effect the effect of the stress stretching the magneticfield is demonstrated. The main component of the total free energy of ferromagneticcrystals is discussed under the external magnetic field and stress, and in accordance withlaw of conservation of energy and thermodynamic principles of dynamic equilibrium themathematical model equation of stress affecting the magnetic properties is established,and the mathematical model equations is parsed, and the calculation result between stressof steel material and their relative permeability is obtained in the different magnetic fieldstrength.(3) A practical method for stress detecting is proposed that is achieved by technicalmagnetization and electromagnetic induction principle based on the relationship oftheoretical analysis between the stress state of steel and its magnetic permeability. Thecorresponding circuit is designed by using the two ways of pulse and sinusoidal signal asthe excitation signal; based on the measured shape and using state of material two kindsof magnetic probes of the U-model and cylinder is designed. Its magnetic circuit analysisis carried out, and the probe has been optimized by finite element simulation software.(4) The prototype of corresponding stress detection system is developed, and themain parameters are analyzed by experiments. According to the different probe structureand excitation the test scheme are designed. By use of calibration method the maintechnical parameters of the detection system prototype is calibrated in the universaldetecting machine to obtain the corresponding test data. The relations of the processeddata and material stress are in a fourthorder curve fitting, and the correlation coefficientsare0.98or more. The impact of the detection value on same materials with the impurityis analyzed. From the test results, this maximum impact of the materials by different manufacturers is less than3%.(5) By use of FLUX electromagnetic field simulation software the electromagneticfield of whole system is analyzed including the size of the magnetic field and thedistribution inside the material, and through the software the correspondence betweenstress and material permeability is calculated and that is consistent with the theoreticalconclusions. Finally, it is proposed that the value of material stress is calibrated by thecombining method of test and numerical simulation to replace the traditional calibrationmethod and obtain good simulation results,which the U-model measurement has the bestsimulation results and the maximum error is less than1%.At last, this dissertation reviews the whole research work and sums up shortcomingsin it,some important issues are expected to be perfected in the near future.