摘要:
由于漏磁检测(MFL)具有操作简单、成本低廉、信号稳定等特点,已被广泛应用于铁磁材料的无损检测.在MFL领域,实现缺陷评估的关键是对漏磁信号与缺陷几何特征之间的关系进行准确描述.本文建立了一个任意方向的表面缺陷漏磁场分布的三维数学模型.首先,将表面缺陷近似为一个有限长的矩形槽来进行描述;然后,从理论上分析了不同缺陷方向下槽壁磁荷密度的变化规律;最后,通过矢量合成得到了有向缺陷的漏磁场分布.开展了仿真和实验,对缺陷在不同磁化方向下的漏磁场分布进行了分析.实验结果表明,缺陷的MFL分布与方向性密切相关.随着与磁化方向夹角增大,缺陷漏磁场水平分量亦增加,单峰性也越突出;但垂直分量却随夹角的增大而呈现双峰分布.所建模型能有效地描述缺陷的方向性对漏磁场分布影响,对优化MFL检测器设计和提高缺陷评估质量有实际指导意义.
Abstract:
Magnetic flux leakage (MFL) has been widely applied to the nondestructive testing (NDT) of ferromagnetic ma-terials due to its simple operation, low cost, and steady signal. Its defects are evaluated based on the relationship between MFL signal and the geometrical characteristic of defect. In this paper, a three-dimensional (3D) mathematical model is developed for the magnetic leakage field of surface-breaking defects that are arbitrarily oriented inside ferro-magnetic material. Firstly, a finite-length rectangular slot is used as a simplified and convenient representation of a surface-breaking defect. Then, the magnetic charge densities of slot walls in different surface-breaking orientations are analyzed theoretically. The distribution of the magnetic leakage field can ultimately be derived by vector synthesis. Both simulations and experiments are conducted to analyze the magnetic leakage field distributions in different magnetization orientations. The results show that with increasing the angle between the defect orientation and the magnetic field, the horizontal component of the leakage magnetic field increases as demonstrated by increasing the prominence of its single peak. At the same time, however, the vertical component shows a bimodal distribution. The proposed model can effectively describe the influence of defect orientation on MFL signals, which can offer practical guidelines for optimizing MFL detectors and improving defect assessment.
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