【作者】 李向东；

【导师】 王泽勇；

【作者基本信息】 西南交通大学 ， 光学工程， 2012， 硕士

【摘要】 超声TOFD(time of flight diffraction)检测系统是通过检测入射超声纵波在缺陷端部产生的衍射波信号,并根据其传播时间差进行缺陷定量与定位的方法。TOFD技术具有缺陷检测结果直观、准确的特点。超声TOFD检测技术具有原理简单、操作便利、检测速度快、对焊缝中裂纹类缺陷检出率高、特别适合于大厚件焊缝检测等优点得到了广泛的应用。本文设计了TOFD检测系统的手动扫查装置,编写了基于VC++的图像处理系统。为了准确定位缺陷深度,针对由于工件表面不平整、扫查速度突变等原因造成检测图像发生畸变弯曲现象,根据TOFD成像原理,采用了基于峰值搜索算法的直通波拉直技术,该方法能够很好地矫正图像,使直通波保持在相同的水平位置；实际焊缝检测过程中采集数据量较大,可以在直通波拉直的基础上提取有效焊缝区域,减少了后期图像处理的数据量,提高了后续处理的效率。缺陷判读作为超声TOFD检测的重要部分主要是由人工操作来完成,消耗了检测人员大量的时间和精力。另外受检测人员的知识、经验和熟练程度的影响,缺陷判读及检测结果往往存在误差,特别是在大量数据处理过程中,甚至会发生错误。因此,为了提高工作效率、降低误判率,本文提出通过频域变换处理后建立D扫图像的背景模型,利用背景减除算法提取有效的焊缝缺陷图形,实现焊缝缺陷目标的自动提取,提高了焊缝缺陷的检测效率及准确性。本文设计的超声TOFD检测系统包括十字光标、抛物线指针光标等人工检测模块,同时可分步实现图像拉直、焊缝区域提取、焊缝缺陷图形提取等功能,验证自动提取焊缝缺陷图形的正确性,具有检测图像清晰,操作过程简单,缺陷位置计算准确等特点。更多还原

【Abstract】 Time of Flight Diffraction Ultrasonic detection method is based on the measurements of the travel time of the echoes diffracted by the defect. It has three kinds of display modes called A-scan, B-scan and D-scan, the detection result is direct and precise. TOFD Ultrasonic detection method has simple principle, convenient operations, fast detection speed, high crack defects detection rate, especially suitable for the thick weld testing and with many other advantages it is widely used in many fields.This paper designed a manual scanning device for the TOFD detection system, write the image processing system based on VC++6.0. In order to locate the depth of defect accurately, due to the image distortion caused by the roughness of surface, or the scanning velocity mutation, and according to the principle of TOFD detection, straighten the lateral waves based on the peak search algorithm, corrected the image very well and make the lateral waves remain at the same level; The actual weld inspection process collects a large amount of data, so extraction the effective weld area based on the previous process, reduced the data of the image, and improve the efficiency of the processing.As an important part of TOFD detection, defect interpretation is mainly accomplished by people, waste a lot of time and energy. In addition, due to the personnel knowledge, experiences and the proficiency of the detector, especially when there is a large amount of data, it may get the wrong result. Therefore, in order to improve work efficiency, and reduce the error rate, In this paper, rebuild the image background of D-scan based on the frequency domain filtering, and using the background difference method to extract effective weld defects, extract the welding defects automatically, improves the efficiency and accuracy of the weld detection.The TOFD inspection system in this paper includes inspection modules such as cross curse and parabola pointer curse, it can straight the lateral wave and extract the effective weld region, according to the original image use the frequency filtering process rebuild the background image, and get the right defects automatically. The experiment shows that this method can extract defect targets accurately.更多还原