本文關(guān)鍵詞： 焊縫裂紋 電磁激勵 紅外熱像法 裂紋識別 有限元　出處：《武漢理工大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：金屬焊縫裂紋一直是大型機械設(shè)備最危險的缺陷之一,運用無損檢測方法檢測缺陷是保障設(shè)備安全運行的關(guān)鍵,電磁激勵紅外熱像技術(shù)是一種新型無損檢測技術(shù),具有非接觸、便攜、效率高等優(yōu)點。本文針對焊縫表面裂紋缺陷,運用電磁激勵紅外熱像法進行檢測,通過理論分析、仿真模擬、試驗驗證以及裂紋識別算法研究,對紅外熱像圖上的異常溫度分布情況進行分析,判斷裂紋的存在,對焊縫裂紋的檢測具有重要價值。本文的主要研究內(nèi)容如下:1)首先介紹了電磁激勵紅外熱像法檢測焊縫裂紋的基本理論,在電磁感應(yīng)理論與渦流效應(yīng)下,建立了焊縫裂紋的渦流場、溫度場數(shù)學(xué)模型,以及裂紋區(qū)域的渦流場、溫度場分布情況,并對影響感應(yīng)加熱效率的激勵參數(shù)做出了理論分析與指導(dǎo)。2)其次運用有限元仿真方法模擬了電磁激勵感應(yīng)加熱及對焊縫裂紋的檢測過程,在COMSOL有限元分析軟件上建立了電磁激勵檢測焊縫裂紋的模型,模擬了鋼板焊縫表面裂紋、近表面裂紋及無裂紋三種情況的熱傳導(dǎo)過程;通過改變表面裂紋的長、寬、高及方向,分析電磁激勵法在裂紋尺寸與形狀檢測方面的規(guī)律;通過改變激勵線圈的激勵頻率與提離高度,說明激勵參數(shù)對裂紋表面溫度分布的影響;通過模擬不同的焊接結(jié)構(gòu),說明電磁激勵熱像法的應(yīng)用范圍。3)最后設(shè)計了電磁激勵熱像法檢測焊縫裂紋的試驗系統(tǒng),并搭建了試驗平臺,包括激勵電源的控制,不同激勵線圈形狀與匝數(shù)的設(shè)計,不同焊接結(jié)構(gòu)和不同裂紋尺寸、方向的加工制作等。通過紅外熱像儀拍攝試驗過程中試件表面的溫度變化,得到在不同變量下的檢測結(jié)果。4)根據(jù)所拍攝的紅外熱像圖的表面溫度分布特性,提出了一種基于形態(tài)學(xué)的裂紋幾何特征識別算法,通過計算熱像圖中連通區(qū)域的長寬比,保留長寬比最大的裂紋區(qū)域,從而提取出裂紋的存在。并在MATLAB平臺上設(shè)計裂紋提取軟件界面,實現(xiàn)了裂紋形狀位置的自動提取,使裂紋識別更加簡捷,降低了操作人員的勞動強度,提高了檢測效率。通過上述研究,驗證了電磁激勵紅外熱像法在金屬結(jié)構(gòu)焊縫裂紋識別中的良好效果,該研究對電磁激勵法在焊縫裂紋檢測應(yīng)用領(lǐng)域奠定了基礎(chǔ)。
[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.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG441.7;TN219

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