【作者】 刘斌；

【导师】 杨理践；

【作者基本信息】 沈阳工业大学 ， 测试计量技术及仪器， 2013， 博士

【摘要】 随着现代工业技术的迅猛发展，铁磁性金属材料在建筑、航空航天、能源、运输等领域得到了广泛的应用。金属构件在使用过程中，局部区域的应力集中使其机械强度大幅度下降，容易引起突发性事故。因此应力检测对金属构件的安全运行有着重要的意义。金属磁记忆检测技术作为一种新兴的无损检测技术已经在很多领域得到了较为成功的应用，其可以有效地检测铁磁性金属构件的微观损伤，具有诊断速度快、操作简单、价格低廉等优势。但是，由于缺乏深层次的理论支持和系统的实验研究，磁记忆现象的物理机理至今还没有定论，磁记忆信号的可靠性和真实性很难让人信服。传统力学和磁学很难建立起磁力学关系来说明磁记忆效应的产生机理，本文从量子力学微观理论出发对磁记忆效应产生的微观机制展开研究，采用基于密度泛函理论的第一性原理研究方法，研究了力对铁磁材料磁性能的影响，对磁记忆自发漏磁信号的产生机理以及应力集中与磁记忆信号的定量变化关系进行了深入的研究。研究了铁磁材料的磁性来源，首次运用量子力学理论解释磁记忆效应的力磁对应关系。在自旋极化体系中，采用第一性原理的计算方法计算了铁磁材料的晶格常数、电子结构、电子自旋态密度、分波态密度、原子磁矩与材料磁特性的定量变化关系；研究了布里渊区划分、交换关联能近似算法、平面波截止能量对计算结果的影响；研究不同的晶体结构下磁记忆效应的力磁关系。研究了外力和外界磁场作用对材料磁特性的影响。体系磁矩随应力集中状态的变化与微观结构的改变密切相关，体系的磁矩会随着最近邻原子间距的变化近似成线性变化，研究了拉应力与压应力作用下，材料磁特性的变化特征。研究了晶格畸变与掺杂元素对材料磁特性的影响。铁磁构件中C、Si、Mn等元素通常以替位式和间隙式的形式掺杂在系统中，研究掺杂前后体系的磁特性。同时，磁记忆效应的产生与晶格结构的改变密切相关，应力集中可能导致材料晶格结构发生各项同性畸变和各项异性畸变，根据应力作用形式确定晶格畸变形式，研究晶格各项同性畸变与各项异性畸变对材料磁特性的影响。理论研究结果表明应力集中导致晶格畸变是磁记忆信号产生的主要原因，即，拉伸作用导致原子磁矩增加，材料的磁性增强；压缩作用导致原子磁矩减小，材料的磁性减弱。钢铁构件中，掺杂元素可以改善材料的机械性能，同时会对材料的磁性产生影响，掺杂前后材料的磁性特性相似。基于第一性原理的研究方法从微观角度解释了金属磁记忆效应的力磁耦合关系，首次对磁记忆现象给出了一种定量计算的方法，同时，为磁记忆效应的物理机理研究提出一种新的研究思路。选取石油天然气长输管道使用的X70钢管进行水压爆破实验，研究磁记忆信号与应力的变化关系。X70号钢主要成分是Fe，其中含有微量C、Si、Mn掺杂元素。磁记忆信号随水压的增加发生变化，实验现象证明了金属磁记忆检测技术在管道应力在线检测领域的应用是可行的。更多还原

【Abstract】 With the rapid development of modern industrial technology, the ferromagnetic metalmaterials have been widely used in construction, aerospace, energy, transportation andother fields. In use process, the mechanical strength will be reduced on stress concentrationlocal of metal components, which is easy to cause sudden accident. So stress testing iscritical to the safe operation of pipelines. Compared with the traditional technique ofnondestructive testing, metal magnetic memory testing technique can effectively detectmicroscopic damage of ferromagnetic components, which advantages are fast diagnosis,simple operation, and low price. However, due to the lack of theoretical support andsystematical experimental study, the physical mechanism of magnetic memoryphenomenon is still not settled yet, reliability and authenticity of the magnetic memorysignal is difficult to be convinced. Traditional mechanical and magnetism are difficult toestablish a magnetic relationship to illustrate the mechanism of magnetic memory effect.The microcosmic mechanism of magnetic memory effect is studied based on firstprinciples calculation, and then the magnetic-force effect of ferromagnetic materials, themechanism of spontaneous magnetic flux leakage signals of magnetic memory andrelationship between stress concentration and magnetic memory signal are analysed.The magnetic source of ferromagnetic materials is studied. The lattice constants,electronic structure, electron spin state density, partial wave state density and thequantitative relationship between atomic magnetic moment and the magnetic properties ofmaterials are calculated by using the basic theory of quantum mechanics, Which providetheoretical basis for the power-magnetic coupling of metal magnetic memory effect. Inspin system, the brillouin zone division, exchange connection, plane wave energy andapproximation algorithm are studied. The ground state of magnetic memory effectproperties are researched under the different crystal structures.The influence of the external forces and external magnetic field on magneticproperties of materials, the test model of magnetic memory effect is established. With thechange of the stress concentration state, magnetic moment is closely related to the microstructure change, and magnetic moment of system will change as the most close tothe atomic spacing approximation into linear change, the characteristics of magnetismunder the action of tensile stress and compressive stress is studied.The influence of the lattice distortion and the doping elements on the materialmagnetism is studied. C, Si, Mn and other elements generally are doped in theferromagnetic component in bit or clearance. The magnetic properties of the doping systemare studied. At the same time, the magnetic memory effect is closely related to the changeof lattice structure, the stress concentration may result in isotropy and anisotropy latticestructure distortion distortion, so the flunence of the lattice distortion on the materialsmagnetism is studied.Thesis theoretical research results show that the lattice distortion which is caused bystress concentration is the primary cause of magnetic memory signal, i.e., under tensileeffect, atomic magnetic moment increases, material’s magnetic largens; under compressioneffect, atomic magnetic moment decreases, material’s magnetic abates. And theoreticalcalculation shows that the trace elements which are doped in the steel component will nothave major influence on the material magnetic. A new method is put forward to study thethe physical mechanism of the magnetic memory effect.The X70steel pipe is used for water pressure blasting experiments, and then therelationship between magnetic memory signal and stress is analysed. The main ingredientof X70steel is Fe, and the trace elements such as C, Si, Mn are doped. The trend is thatmagnetic memory signals change with the increase of water pressure, and the experimentphenomenon shows that the application of metal magnetic memory testing technology inon-line detection of pipe stress is feasible.更多还原