外界磁场对铁磁性材料金属磁记忆检测影响的研究

发布时间：2019-04-20 13:10

【摘要】：微观和宏观应力集中区域是金属构件和机器部件发生损伤的主要部位。常规的无损检测方法在管道及铁磁性材料试件的缺陷检测等方面具有重要意义，但无法切实有效的预防由于各种微观应力集中区域引起的突发性事故。近年来发展起来的金属磁记忆检测方法是通过对铁磁性材料进行早期诊断以达到预防的目的。但由于该技术理论尚不完善，影响因素众多，在工程应用中外界磁场对金属磁记忆检测的影响尚不能定量评估，故研究外界磁场对磁记忆检测方法的影响十分必要。本文研究能量平衡理论、电磁场理论及J-A磁机械效应理论等，利用不同理论分析在磁记忆检测过程中外界磁场对检测结果的影响，从而证明外界磁场可能掩盖磁记忆信号。通过以钢筋及冷拔棒等具有代表性的铁磁性材料做为实验试件，利用永磁铁磁场模拟外界磁场，对存在应力的钢筋及冷拔棒在外界磁场环境下进行金属磁记忆检测。检测结果显示在外界磁场影响下铁磁性材料的弹性阶段应力集中区域磁记忆信号消失，，磁场环境下重复受力后磁记忆信号即可被重新识别；塑性阶段应力集中区域磁记忆信号不会因外界磁场出现明显的变化。根据理论分析与实验检测结果，结合金属磁记忆磁畴壁聚合模型，铁磁性材料在外界磁场的磁化作用下，内部磁畴会发生偏转或者位移形成残余应力，在弹性阶段由于外加应力相对残余应力较小，应力集中区域磁记忆信号容易被外界磁场信号所掩盖，导致磁记忆信号消失。磁场环境下重复受力会增加外加应力抵消残余应力作用，磁记忆信号重新显现。对于塑性阶段由于外加应力远大于外界磁场所致的残余应力，故会不产生明显影响。根据理论分析与实验检测结果表明，在外界磁场环境下金属磁记忆检测方法在施加应力较小时，弹性阶段应力集中区域磁记忆信号被抵消；当外加应力增加后，外界磁场影响效果减小。外界磁场不会对塑性阶段金属磁记忆信号产生明显影响。因此，金属磁记忆是一种有效可靠的早期诊断方法，具有普遍的适用性。
[Abstract]:Micro-and macro-stress concentration areas are the main damage areas of metal components and machine components. The conventional non-destructive testing (NDT) method is of great significance in the defect detection of pipes and ferromagnetic materials, but it can not effectively prevent the sudden accidents caused by various micro-stress concentration areas. The metal magnetic memory detection method developed in recent years is to achieve the purpose of prevention by early diagnosis of ferromagnetic materials. However, because the theory of this technique is not perfect and there are many influencing factors, the influence of external magnetic field on metal magnetic memory detection can not be quantitatively evaluated in engineering application, so it is necessary to study the influence of external magnetic field on magnetic memory testing method. In this paper, the theory of energy balance, the theory of electromagnetic field and the theory of JA magneto-mechanical effect are studied, and the influence of external magnetic field on the results of magnetic memory testing is analyzed by using different theories, so as to prove that the external magnetic field may cover up the magnetic memory signal. By using typical ferromagnetic materials such as steel bar and cold-drawn bar as experimental specimens and using permanent magnet magnetic field to simulate the external magnetic field, the metal magnetic memory of steel bars and cold-drawn bars with stress in the external magnetic field environment was tested. The results show that the magnetic memory signal in the elastic phase of ferromagnetic material disappears under the influence of external magnetic field, and the magnetic memory signal can be re-recognized after repeated stress in the magnetic field environment. In the plastic stage, the magnetic memory signal in the stress concentration region does not change obviously due to the external magnetic field. According to the theoretical analysis and experimental results, combined with the metal magnetic memory domain wall polymerization model, the internal magnetic domain deflection or displacement will occur in ferromagnetic materials under the magnetization of the external magnetic field to form residual stress. In the elastic stage, the magnetic memory signal in the stress concentration region is easily masked by the external magnetic field signal because the applied stress is relatively small relative to the residual stress, which leads to the disappearance of the magnetic memory signal. The repeated stress in the magnetic field will increase the applied stress to counteract the residual stress, and the magnetic memory signal will appear again. In plastic stage, the residual stress caused by external magnetic field is much larger than that caused by applied stress, so there is no obvious influence on the residual stress caused by external magnetic field. According to the theoretical analysis and experimental results, it is shown that the magnetic memory signal in the stress concentration region of the elastic phase is counteracted by the metal magnetic memory detection method in the environment of external magnetic field when the applied stress is small. When the applied stress increases, the effect of external magnetic field decreases. The external magnetic field has no obvious effect on the metal magnetic memory signal in plastic stage. Therefore, metal magnetic memory is an effective and reliable early diagnosis method, which has universal applicability.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG115.28

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