【作者】 王阳；

【导师】 林莉；

【作者基本信息】 大连理工大学 ， 材料无损检测与评价， 2019， 硕士

【摘要】 工程中存在大量带余高对接焊缝,采用射线检测时易造成面积型缺陷漏检、检出缺陷无法准确定位;采用传统超声检测存在耦合困难、信号识别困难和检出率低的问题。为解决上述问题,本文基于相控阵超声检测(Phased Array Ultrasonic Testing,PAUT)技术开展带余高对接焊缝检测研究,通过仿真模拟和实验结合方式给出较优检测参数。考虑带余高焊缝检测空间受限和避免检测区域漏检,基于直入射检测采集信号开展全聚焦方法(Total Focusing Method,TFM)成像检测研究。具体研究内容如下:(1)针对加工的长宽高260 mm×30 mm×40 mm、余高曲率半径6 mm、余高高度2.4 mm的30#钢试块进行声速和衰减系数测量,建立仿真模型开展PAUT研究。结果显示:采用在基体上声波斜入射检测Φ2 mm横通孔信噪比(49.1 dB)远远高于探头在焊缝上方声波直入射检测(3.1 dB)。在此基础上研究斜入射检测声场仿真规律:随着偏转角度增加,检测范围增大、检测分辨力先升高后降低、检测灵敏度降低;随着聚焦深度增加,检测范围增大、检测分辨力和检测灵敏度均降低。针对深度20 mm横通孔实验和仿真获得较优检测参数为:40°~60°偏转角度和20 mm聚焦深度。(2)考虑探头斜入射检测空间受限、直入射检测信噪比低问题,基于直入射方式采集A扫信号,对比分析B扫描(B-scan)、合成孔径聚焦技术(Synthetic Aperture Focusing Technique,SAFT)、表面契合超声(Surface Adaptive Ultrasound,SAUL)法和TFM在轮廓提取方面差异。结果显示:SAFT轮廓提取最大误差和平均误差最小,分别为0.31 mm和0.04 mm;TFM轮廓提取归一化标准差最接近1 mm,为0.98 mm。基于利用这些方法提取轮廓进行焊缝内部Φ2 mm横通孔成像结果发现:TFM效果最好、B-scan和SAFT次之、SAUL最差。利用TFM的横通孔幅值和信噪比分别达到-14.22 dB和17.56 dB。(3)为提高带余高对接焊缝TFM成像效率,以每个发射信号对应所有接收信号中最大幅度1/4作为阈值筛选形成动态有效孔径(Dynamic Effective Aperture,DEA)参与轮廓成像,结果显示该轮廓和全孔径(Full Aperture,FA)提取轮廓完全一致。基于该方法提取轮廓实验获得Φ2 mm横通孔信噪比和幅值分别为-21.39 dB和7.51 dB,低于仿真结果的-14.22 dB和17.56 dB,这是由于试块表面存在刀痕,影响声能入射和声束叠加。在此基础上深入研究带余高对接焊缝余高尺寸对检测结果影响,结果显示:当焊缝余高高度为2.4 mm时,随着余高曲率半径增加,Φ2 mm横通孔幅值和信噪比均呈现升高趋势;当焊缝余高曲率半径为18 mm时,随着余高高度度加,Φ2 mm横通孔幅值和信噪比均呈现降低趋势。分析该现象是由结构和轮廓提取误差两方面引起。更多还原

【Abstract】 There are a large number of butt welds with caps in engineering.In the process of radiography testing,it’s difficult to detect the planar defects.Otherwise,the detected defects cannot be accurately positioned.The traditional ultrasonic testing has the problems of coupling,signal identification and low detection efficiency.In order to solve these problems,phased array ultrasonic testing(PAUT)technology is used to inspect the butt welds with caps in this paper.By simulation,we analyzed the acoustic field propagation laws of the universal phased array probe with the wedge in welds and got optimized inspection parameters.Due to the limited space of inspection and for the implementation of larger area inspection,Imaging of butt weld is carried out using total focusing method(TFM).The specific research contents are as follows:30# steel butt weld testing block was machined with a dimension of 260 mm×30 mm×40mm,which had a 6 mm curvature radius and 2.4 mm cap height.Based on the sound velocity and attenuation coefficient of the block,and the simulation model was established to carry out PAUT research.The results show that the signal-to-noise ratio(49.1 dB)of the Φ2 mm SDHs detected with the obliquely incident wave on the base is much higher than that of the directly incident wave above the weld(3.1 dB).Furthermore,based on the model,we carried out a research of the obliquely incident wave and analyzed the acoustic field.The results show that with the increase of deflection angle,the detection coverage increases,the detection resolution increases first and then decreases,the detection sensitivity decreases at the same time.And as focusing depth increases,the detection coverage increases and the detection resolution decreases.The preferred detection parameters for the 20 mm SDH are: 40° to 60°deflection angle and 20 mm depth of focusing.Considering the limitation of oblique incident wave and the low signal-to-noise ratio of the direct incident wave,the A-scan signals were acquired using the universal phased array probe by water immersion.Based on the signals,differences of contour extraction were compared and analyzed among B-scan,Synthetic Aperture Focusing Technique(SAFT),Surface Adaptive Ultrasound(SAUL)and Total Focusing Method(TFM).Among these four methods,The results show that the maximum error and average error of SAFT contour extraction are 0.31 mm and 0.04 mm,respectively,which are also the smallest.The normalized standard error of TFM contour extraction is 0.98 mm,which is closest to 1 mm.Further imaging results of the SDH in the weld were compared based on extracted contour of these methods: The result of TFM is the best,That of B-scan and SAFT are the second,SAULis the worst.The amplitude and signal-to-noise ratio of the SDH are-14.22 dB and 17.56 dB by TFM,respectively.In order to improve the calculation efficiency of TFM imaging of butt welds,the signal threshold which is the maximum amplitude of 1/4 of all received signals for each transmitted signal was used to form the dynamic effective aperture(DEA)to participate in the imaging.The result shows that the extracted profile is completely consistent with that of full aperture(FA).The amplitude and signal-to-noise ratio of the Φ2 mm SDH in experiment are-21.39 dB and 7.51 dB,respectively.The amplitude and signal-to-noise ratio of the Φ2 mm SDH in simulation are-14.22 dB and 17.56 dB,respectively.Due to the presence of tool marks on the surface of the block,the experimental results are lower than that of simulation.On this basis,A research was carried out about the effect of weld size on image quality.The results show that when the height of the weld cap is 2.4 mm,with the increase of curvature radii,the amplitude and signal-to-noise ratio of the SDH increase,with the increase of cap height,the amplitude and signal-to-noise ratio of the Φ2 mm SDH decrease when the curvature radius of the weld cap is 18 mm.These phenomena are caused by structure and extracted contour errors.更多还原