磁化状态及环境磁场对磁记忆信号的影响

发布时间：2018-05-26 08:41

本文选题：金属磁记忆检测 + 力磁耦合　；参考：《南昌航空大学》2017年硕士论文

【摘要】：金属磁记忆信号是弱磁信号,容易受很多因素的影响,以至于金属磁记忆方法不能为工程实践提供可靠的、准确的检测。本论文主要从试验研究和理论研究分析磁化状态、环境磁场和热处理工艺对金属磁记忆信号变化规律的影响。对三种不同磁化状态的Q235钢平板工件进行静载拉伸试验,探讨了磁化状态对磁记忆信号和力磁耦合关系的影响。试验结果表明:在弹性阶段和塑性变形的初始阶段,对于磁化的试件,应力是使初始磁化状态不断向无磁滞磁化状态靠近的过程,而磁化状态的改变量由初始磁化状态与无磁滞磁化状态之间的距离决定。磁化试件的表面所有采样点的力磁变化趋势整体呈“聚拢"的趋势;而对于未磁化的工件,应力使试件磁化,所有点的力磁变化趋势整体却呈“张开"的趋势;在塑性变形的稳定阶段,对于磁化和未磁化的工件,磁化强度变化量都较小,基本保持稳定。对六种不同环境磁场作用下的45#钢圆棒试件进行静载拉伸试验,探讨环境磁场对磁记忆信号和力磁耦合关系的影响。试验结果表明:外加磁场不能改变磁记忆信号曲线和力磁关系曲线的形状,但可以改变它们值的大小;在一定的磁场范围内,应力引起的磁记忆信号值随环境磁场的增加而增加,但当环境磁场超过某一临界值时,磁记忆信号值反而随环境磁场的增加而减少;当环境磁场为零或完全被抵消时,应力却不能产生磁化效应,力磁关系曲线为一条水平的直线。观察五种不同热处理工艺金相试样40Cr钢圆棒的显微组织,并测量试样表面点的磁记忆信号值。结果表明:试件经标准淬火之后,随回火温度的升高,磁记忆信号值不断增大,抗拉强度不断减小,但塑性却不断增强。对五种不同热处理工艺的拉伸试样40Cr钢圆棒进行静载拉伸试验,探讨热处理工艺对磁记忆信号的影响。试验结果表明:对于原始退火、中温回火和高温回火的拉伸试样,它们的磁记忆信号曲线和梯度曲线的变化规律近似相同;对于标准淬火和低温回火的拉伸试样,它们的磁记忆信号曲线和梯度曲线的变化规律近似相同。因此在金属磁记忆检测的实践中,特别是在定量检测的应用中必须考虑环境磁场的影响,且被检测构件的初始磁化状态和热处理工艺不可忽略。
[Abstract]:Metal magnetic memory signal is a weak magnetic signal, which is easily affected by many factors, so that metal magnetic memory method can not provide reliable and accurate detection for engineering practice. In this paper, the effects of magnetization state, environmental magnetic field and heat treatment process on the variation of metal magnetic memory signal are analyzed in terms of experimental and theoretical studies. Static tensile tests were carried out on three Q235 steel plate workpieces in different magnetization states, and the effect of magnetization state on magnetic memory signal and magneto-magnetic coupling was discussed. The experimental results show that in the elastic stage and the initial stage of plastic deformation, the stress of the magnetized specimen is the process of making the initial magnetization state approach to the unhysteresis magnetization state continuously. The change of the magnetization state is determined by the distance between the initial magnetization state and the unhysteresis magnetization state. For the unmagnetized workpiece, the stress causes the magnetization of the specimen, but the trend of the change of the force and magnetism of all the points is "open" as a whole, and the trend of the change of the force and magnetism of all the sampling points on the surface of the magnetized specimen is "converging" as a whole, while for the unmagnetized workpiece, the stress makes the sample magnetized. For both magnetized and unmagnetized workpieces, the change of magnetization intensity is small and stable in the stable stage of plastic deformation. The static load tensile test of four steel round bar specimens under six different environmental magnetic fields was carried out to investigate the effect of environmental magnetic field on the coupling relationship between magnetic memory signal and force magnetic field. The experimental results show that the applied magnetic field can not change the shape of the magnetic memory signal curve and the magneto-magnetic relation curve, but can change the magnitude of their values, and in a certain magnetic field range, The magnetic memory signal caused by stress increases with the increase of the ambient magnetic field, but when the ambient magnetic field exceeds a certain critical value, the magnetic memory signal value decreases with the increase of the ambient magnetic field, and when the ambient magnetic field is zero or completely offset, However, the stress does not produce magnetization effect, and the magneto-force relation curve is a horizontal straight line. The microstructure of the 40Cr steel rod of five different heat treatment processes was observed, and the magnetic memory signal of the surface of the sample was measured. The results show that the magnetic memory signal value increases and the tensile strength decreases, but the plasticity increases with the tempering temperature rising after standard quenching. The static tensile test of 40Cr steel round bar with five different heat treatment processes was carried out, and the effect of heat treatment process on magnetic memory signal was discussed. The experimental results show that the variation of magnetic memory signal curve and gradient curve are approximately the same for the tensile specimens with original annealing, moderate tempering and high temperature tempering, and the tensile specimens with standard quenching and low temperature tempering, Their magnetic memory signal curves and gradient curves are approximately the same. Therefore, in the practice of metal magnetic memory testing, especially in the application of quantitative testing, the influence of environmental magnetic field must be considered, and the initial magnetization state and heat treatment process of the tested components should not be ignored.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG115.284

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