Compared to penetration and magnetic powder methods,the pulse eddy current thermography is a more environmentally friendly non-destructive testing technology for surface crack of metal,and its detection result is closely related to the surface shape of tested objects.At present,the research on such topic is only focusing on the plane and regular cylindrical parts,while lack of analysis of the parts with more complex shapes.With screw rod as the detected object,by using COMSOL,the model of screw rod excited by electromagnetic field is established;and the law of sample surface temperature rise and Joule heat distribution under axial and circumferential magnetization methods are analyzed,and compared with the experimental results for verification.The results show that,under axial magnetization,the detection sensitivity of the crack at the root of the thread is lower because of the magnetic leakage,while under circumferential magnetization,the sensitivity is higher because the circumference decreases and the cross sectional area of eddy current decreases.In addition,the thermal diffusion and aggregation can lead to a higher temperature at the edge of the thread rod and disturb the display of crack;it needs to subtract the reference thermograph of the sample without crack to identify the crack.These researches can act as a theory reference in the process of design for pulsed eddy current thermography system for detecting parts with complex shape.%脉冲涡流热成像是一种相比渗透和磁粉方法更环保的金属表面裂纹无损检测技术,其检测效果与测试对象表面形状密切相关.现有研究仅关注平面和规则圆柱,缺少对更复杂形状零部件检测规律的分析.以螺杆为对象,采用COMSOL软件建立电磁激励螺杆模型,分析轴向和周向磁化方法下试样表面温升和焦耳热分布的规律,并与螺杆试样温升分布规律进行对比验证.结果显示:在轴向磁化时,漏磁等效应导致螺纹牙底裂纹检测灵敏度低;而在周向磁化时,螺纹牙底处周长减小使该处涡流截面积减小,该处裂纹检测灵敏度反而提高.热扩散和边缘热聚集效应会导致螺纹边缘处温度显著偏高并干扰裂纹显示,需与无裂纹参考图像相减对裂纹进行识别.该研究结果可作为复杂形状零部件脉冲涡流热成像检测系统设计过程的理论参考.
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