【作者】 李喆；

【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， 2015， 硕士

【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。更多还原

【Abstract】 Micro and macro stress concentration area is the main site of metal components andmachine parts where is occur damage.Conventional NDT methods has important significancein defecting of detection pipeline and ferromagnetic material specimen, etc., but can not beeffective in preventing of sudden accident which is caused by a variety of micro stressconcentration region. MMM detection method which is developed in recent years is throughthe early diagnosis to ferromagnetic material in order to prevent.However, due to the technicaltheory is not perfect, and many other factors,the outside influence of magnetic field on toexternal the metal magnetic memory testing in engineering applications can not yet bequantitative assessed, so the studying of the method of the influence of the external magneticfield on the magnetic memory testing is necessary.This paper is study the energy balance theory, electromagnetic theory and J-Amagneto-mechanical effect theory, using different theories to analyze the influence of theexternal magnetic field on the test results during the magnetic memory testing process,thusproving the external magnetic field may mask Magnetic Memory Signal.By steel bars, colddrawn rods and other representative ferromagnetic material as a test specimen, using anexternal magnetic field to simulate the permanent magnet field, make the metal magneticmemory testing of the existence of stress steel and cold drawn rods in the external magneticfield.Test results show that the stress concentration area of magnetic memory signal disappearsunder the influence of an external magnetic field in a ferromagnetic material elasticstage,under the magnetic field after repeated force magnetic memory signal can bere-identification.Plastic stage stress concentration area of magnetic memory signal does notoccur significant changes in the external magnetic field. According to the theoretical analysisand experimental test results, combined MMM magnetic domain wall aggregation model,ferromagnetic material under the action of external magnetic field in the magnetization, whichinternal magnetic domain will occur deflection or displacement to form residual stress. In theelastic stage due to the applied stress relatively residual stresses is small, stress concentrationarea of magnetic memory signal is easily overshadowed by the external magnetic field signal,resulting in magnetic memory signal disappears. Under the magnetic field environment therepeated force will increase applied stress to offset the residual stress., the magnetic Memory Signal resurfaced. Due to the applied stress is much greater than the residual stress which iscaused by the external magnetic field in plastic stage, it will not have a significant impact.According to the theoretical analysis and experimental test results show, during metalmagnetic memory testing method when applied stress is small in the external magnetic field,elastic stage stress concentration area magnetic memory signal is canceled. When the appliedstress increases, the effect of the influence of the external magnetic field reduce. Externalmagnetic field does not have a significant effect on the plastic stage MMM signals. Therefore,MMM is an effective and reliable method for early diagnosis which has general applicability.更多还原