基于电磁激励的焊缝裂纹红外热像检测数值模拟与试验研究

发布时间：2018-02-28 08:12

本文关键词： 焊缝裂纹电磁激励红外热像法裂纹识别有限元　出处：《武汉理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：金属焊缝裂纹一直是大型机械设备最危险的缺陷之一,运用无损检测方法检测缺陷是保障设备安全运行的关键,电磁激励红外热像技术是一种新型无损检测技术,具有非接触、便携、效率高等优点。本文针对焊缝表面裂纹缺陷,运用电磁激励红外热像法进行检测,通过理论分析、仿真模拟、试验验证以及裂纹识别算法研究,对红外热像图上的异常温度分布情况进行分析,判断裂纹的存在,对焊缝裂纹的检测具有重要价值。本文的主要研究内容如下:1)首先介绍了电磁激励红外热像法检测焊缝裂纹的基本理论,在电磁感应理论与涡流效应下,建立了焊缝裂纹的涡流场、温度场数学模型,以及裂纹区域的涡流场、温度场分布情况,并对影响感应加热效率的激励参数做出了理论分析与指导。2)其次运用有限元仿真方法模拟了电磁激励感应加热及对焊缝裂纹的检测过程,在COMSOL有限元分析软件上建立了电磁激励检测焊缝裂纹的模型,模拟了钢板焊缝表面裂纹、近表面裂纹及无裂纹三种情况的热传导过程;通过改变表面裂纹的长、宽、高及方向,分析电磁激励法在裂纹尺寸与形状检测方面的规律;通过改变激励线圈的激励频率与提离高度,说明激励参数对裂纹表面温度分布的影响;通过模拟不同的焊接结构,说明电磁激励热像法的应用范围。3)最后设计了电磁激励热像法检测焊缝裂纹的试验系统,并搭建了试验平台,包括激励电源的控制,不同激励线圈形状与匝数的设计,不同焊接结构和不同裂纹尺寸、方向的加工制作等。通过红外热像仪拍摄试验过程中试件表面的温度变化,得到在不同变量下的检测结果。4)根据所拍摄的红外热像图的表面温度分布特性,提出了一种基于形态学的裂纹几何特征识别算法,通过计算热像图中连通区域的长宽比,保留长宽比最大的裂纹区域,从而提取出裂纹的存在。并在MATLAB平台上设计裂纹提取软件界面,实现了裂纹形状位置的自动提取,使裂纹识别更加简捷,降低了操作人员的劳动强度,提高了检测效率。通过上述研究,验证了电磁激励红外热像法在金属结构焊缝裂纹识别中的良好效果,该研究对电磁激励法在焊缝裂纹检测应用领域奠定了基础。
[Abstract]:Metal weld crack has always been one of the most dangerous defects in large mechanical equipment. Nondestructive testing is the key to ensure the safe operation of the equipment. Electromagnetic excitation infrared thermal imaging technology is a new type of nondestructive testing technology with non-contact. In this paper, the electromagnetic excitation infrared thermal image method is used to detect the weld surface crack defects, which is studied by theoretical analysis, simulation, test verification and crack identification algorithm. The abnormal temperature distribution on the infrared thermal image is analyzed, and the existence of the crack is judged. The main research contents of this paper are as follows: (1) the basic theory of electromagnetic excitation infrared thermal image method for detecting weld crack is introduced firstly. Under the electromagnetic induction theory and eddy current effect, The eddy current field, temperature field mathematical model of weld crack and the distribution of eddy current field and temperature field in crack region are established. The excitation parameters affecting the efficiency of induction heating are theoretically analyzed and guided. Secondly, the electromagnetic excitation induction heating and the detection process of weld crack are simulated by using finite element simulation method. In this paper, a model of electromagnetic excitation for weld crack detection is established on COMSOL finite element analysis software, and the heat conduction process of weld surface crack, near-surface crack and non-crack is simulated, and the length, width, height and direction of surface crack are changed. By changing the excitation frequency and lift height of the exciting coil, the influence of the excitation parameters on the temperature distribution of the crack surface is explained, and the different welding structures are simulated, by analyzing the law of the electromagnetic excitation method in the detection of the crack size and shape, and by changing the excitation frequency and the lift height of the excitation coil, Finally, the test system of electromagnetic excitation thermal image method for detecting weld crack is designed, and the test platform is built, including the control of exciting power supply, the design of different exciting coil shape and turn number. Processing and fabrication of different welding structures, different crack sizes and directions etc. The surface temperature change of the specimen was recorded by the infrared thermal imager during the test. According to the surface temperature distribution of the infrared thermal image taken, a morphology-based geometric feature recognition algorithm for crack is proposed. The aspect ratio of the connected region in the thermal image is calculated by calculating the length and width ratio of the connected region. The crack region with the largest aspect ratio is retained to extract the existence of the crack. The interface of the crack extraction software is designed on the MATLAB platform, which realizes the automatic detection of the crack shape and position, and makes the crack identification more concise. The labor intensity of the operator is reduced and the detection efficiency is improved. Through the above research, the good effect of the electromagnetic excitation infrared thermal image method in the weld seam crack identification of metal structure is verified. This study lays a foundation for the application of electromagnetic excitation method in weld crack detection.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG441.7;TN219

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