Study On The Mechanism And Application Of Stress Measurement Based On The Megneto-mechanical Coupling Theory

Most large ferromagnetic components were widely used in large infrastructure and equipment.The safety of ferromagnetic components has a direct relation to people's lives and property.Because of convenient,accurate and non-destructive,magnetic method were attracted more and more attention to evaluate the stress state of ferromagnetic components in engineering application.Based on the theory of ferromagnetism,we systematically discussed the magnetomechanical coupling mechanism from micro and macro aspects,and studied the corresponding theory model.Then we built the coupling relation of stress,magnetic and voltage,and carried out some theoretical studies,experimental explorations and engineering practices around the relation between magnetic properties and stress.The main achievements and innovations were listed as below:In this dissertation,it researched the magneto-mechanical coupling mechanism from the micro and macro fields.By using the domain theory,we discussed the domain motion and the distribution of magnetic energy under stress and external magnetic field.Based on the Jiles-Atherton model,there was discussed the mechanism of magnetomechanical coupling and studied the variation law of stress-induced magnetoanisotropy.Furthermore,the two established models about the permeability and voltage model,the stress and voltage model can prove the proportional relationship between the principal stress and output voltage.On this basis,a testing system was set up to research the effect of stress on magnetic characteristics.Based on results of finite element method simulation,several parameters of the probe were optimized.We got the variation law of the voltage and the iron loss changed with length of probe.In the meanwhile,we also obtained three different relations,such as the relationship of the wire diameter of the coil,the impedance and inductance;the relationship of the voltage,the frequency,the number of turns;and the relationship of inductive reactance of coil,frequency and turns.A new method was adopted to realize the fast and uniform magnetization of samples and enhance the magnetization effect.In the progress of measuring retained austenite with the magnetic method,the principle and test method of was discussed,and the quantitative relationship between austenite content and permeability can be obtained.Through the tension of samples,two relationship were obtained,and the one was inverse relation between the permeability and excited voltage,and the other was proportional relation between the detected voltage and excited voltage.By the obtained relation of stress,detected voltage,permeability and the excited voltage,it verified that the permeability decreases with the increase of stress.The correctness of magnetic method was verified through the tensile test of flat plate with hole and the bending test of cantilever beam.By comparing the results of the finite element method,strain gauge method and magnetic method,we can verify the accuracy and reliability in the load stress test of ferromagnetic components.In addition,it was the first time to propose to distinguish the stress on ferromagnetic components caused by self-weight or external load with the magnetic method.In the meanwhile,the magnetic method was can be used to test the distribution of the residual stress on the welding seam of high-pressure vessel and the automobile flange made by different heat treatment processes.By comparing the results of many methods in different fields,it can prove that the reliability and correctness of magnetic method.There are 86 figures,39 tables,and 239 references in this dissertation.