Experiments of Influencing Factors in the Magneto-mechanical Effect
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カテゴリ: 第7回
School of Aerospace, Tsinghua University LiQiang ZHONG School of Aerospace, Tsinghua University LuMing LI
1 Introduction
have been carried out to study the key factors in Stress concentration caused by loading or magneto-mechanical effect which are fatigue is a potential safety hazard to metal stress[9][10][11] environmental field[11][12], and materials; its testing method is always a focus of material. The results showed that there are laws nondestructive testing researchers. Since it was based on these factors which govern the discovered that stress in ferromagnetic material abnormal change of magnetic field caused by can cause magnetization changes, researchers stress concentration. Furthermore, it is possible have tried to use weak magnetism technology in to roughly predict the stress concentration status nondestructive stress testing. Examples of this by using these laws. include the metal magnetic memory method and the weak magnetic method (!][2][3]. The law of 2 Theory approach had analyzed the magneto-mechanical Using the finite element method, effect and summarized a mathematical model for ferromagnetic metal parts can be viewed as the magnetization change under the conditions being composed of many small elements. The that the stress and material are uniformlydistribution of stress and material in each distributed and the environmental field iselement is uniform, which means that the law of weak[5][6]. However, since the conditions in this approach can used to predict the magnetization model were simplified, it is hard to use thischange of each element. Formula 5-1 is one key model to predict the effect of stressformula in the law of approach introduced by concentration when the stress is nonlinearly Jiles.D.C [5]: distributed and the environmental field isHejj = H + aM + Lepiv;(0) M2 -1 5-1 complicated. In order to determine whether the＝= H + aM + Fo(1M2-157-0 vp (0)) weak magnetism methods are valid for evaluating the safety status of stress concentration, in the last ten years, experiments1900/02/08
1900/10/20where H is the environmental field, M iswhere a = k/MOMS), & is a coefficientthe intensity of magnetization, o is the strain,and imi-12-0(0) is the Taylor serieswith dimensions of energy per unit volume, and W is the elastic energy per unit volume.However, the magnetization intensity a??Ma?? is also a variable in formula 5-1, which means that the effects of these factors are compounded and their influence becomes more complicated than what is discussed in this section.expansion of magnetostriction. In the formula, the magneto-mechanical effect is viewed as an equivalent magnetizing field.The effect of stress is described as a polynomial in formula 5-1. When the strain3 Experimentsincreases, Hejf becomes larger. Since therelationship between o and Hejf is nonlinear,effects from stress concentration should be more significant when the strain increases. The effect of magnetostriction is similar but not the same,Figure 3.1 Experiment System though it is divided into Taylor series expansion. The experimental system we used to studyEnvironmental field is the third factor. the magneto-mechanical effect is as shown in However, it is only considered as a linearFigure 3.1, which is made up by following parts: component and the effects of the environmental A: 3D Helmholtz Coil to control the field can cancel each other out in nearbyenvironmental field; B: Portable Tensile Means elements. Since the leakage surface field tested to apply a controllable tension force; with the weak magnetism method is the differing C:Specimens; D: Flux Gate Magnetometer and results of the magnetization among elements, the Tesla Magnetometer to test the environmental abnormal surface field change may be stable field produced by the 3D Helmholtz Coil; E: 3Dwhen the environmental field is in a high level. Displacement Controller to hold the testing Effects from stress concentration should be moreignificant when the strain increases. The effect of magnetostriction is similar but not the same,Figure 3.1 Experiment System hough it is divided into Taylor series expansion. The experimental system we used to studyEnvironmental field is the third factor. the magneto-mechanical effect is as shown in However, it is only considered as a linearFigure 3.1, which is made up by following parts: component and the effects of the environmental A: 3D Helmholtz Coil to control the Field can cancel each other out in nearbyenvironmental field; B: Portable Tensile Means elements. Since the leakage surface field tested to apply a controllable tension force; with the weak magnetism method is the differing C:Specimens; D: Flux Gate Magnetometer and Cesults of the magnetization among elements, the Tesla Magnetometer to test the environmental abnormal surface field change may be stable field produced by the 3D Helmholtz Coil; E: 3D when the environmental field is in a high level. Displacement Controller to hold the testing However, it should be noted that the abnormalsensor and scan the surface field automatically; changes are obvious when the environmental F: Wireless Micro-magnetic Detector and the field is increasing from zero because theGMR Sensor which were self-developed with a magnetic distribution in weak magnetictesting accuracy of 50nT; G:Computer to control environment also depends on the surface shape the sensor movement and analyze the testing and totally different from the uniformresults. distribution when the environmental field isThe flat-type specimen as shown in Figure zero.3.2 has a regular round hole in center, and stress Using a??Hefta?? as solved for in formula 5-1, concentration is generated around the hole when the magnetization value can be calculated with tensile force is applied to the specimen by the formulas 5-2 and 5-3:portable tensile means.Man (H,0) = M, [coth (**)-] 5-2helpt = (Man a?“ M) + event2019/05/03- 295 --1900/01/11
“ “Experiments of Influencing Factors in the Magneto-mechanical Effect“ “LiQiang ZHONG,LuMing LI