航空涡轮盘件的相控阵超声检测技术研究

发布时间：2018-11-07 13:00

【摘要】：航空涡轮盘是航空发动机的核心部件,制造中由于工艺参数波动可能导致偏析、夹杂物、孔洞、裂纹等各类缺陷;服役过程受力复杂、条件严苛,往往产生疲劳裂纹缺陷,而航空涡轮盘即使存在微小缺陷也可能造成严重后果,因此对其进行出厂和在役的无损检测显得十分必要。相控阵超声检测技术是一种可通过电子方法实现声束变角、深度变焦的无损检测技术,避免了常规单晶探头因移动范围、声束角度有限而引起缺陷漏检。此外,相控阵超声检测技术的声场能控制能力强、检测能量高,可有效提高检测精度和检测效率。根据相控阵超声检测技术的特点,相控阵超声检测技术有望对复杂结构的高温合金航空涡轮盘中的各类缺陷进行准确、高效的无损检测。相控阵超声检测技术在对航空涡轮盘进行检测时,由于其体积大、结构复杂且组织结构粗大,当微小缺陷位于航空涡轮盘近表面、底面、复杂结构区域时,由于缺陷信号容易混淆、信噪比低,缺陷检测容易出现漏检或误检。因此,分析相控阵超声声场分布特点及其影响因素以优化检测参数、分析检测信号并提出相应的信号处理算法对检测信号及图像进行降噪处理是航空涡轮盘相控阵超声检测技术的主要研究内容。首先,理论分析阵元数、阵元间距、频率等参数对航空涡轮盘相控阵超声声场的影响,结果表明:相控阵超声聚焦声场能量随阵元数的增加、频率的提高而增强;相控阵超声栅瓣幅度随阵元间距的增大而增大。第二,试验分析盘件中超声相控阵声场特性,测量航空涡轮盘中相控阵超声焦区宽度及信号幅值随阵元数及聚焦深度的变化规律,结果表明:相控阵超声焦区宽度随阵元数的增加而减小,随聚焦深度的增加而增大;采用相控阵超声斜探头对半径为50mm圆弧上分布的间隔横孔进行检测成像试验,并分析阵元数、探头布置位置对检测分辨率的影响,结果表明:增加阵元数、适当调整探头位置使与横孔图像相交的扫查线角度间隔增大有利于提高检测分辨率。第三,采用超声相控阵斜探头对航空涡轮盘中槽型缺陷进行检测成像试验,深入分析航空涡轮盘中面型缺陷的超声相控阵成像方法及其图像特征,并根据窄槽衍射回波形成的相互分离条纹测量出窄槽缺陷的取向和尺寸,同时分析了阵元数、探头布置位置对窄槽检测精度的影响,结果表明:相控阵超声测长值总体要稍大于窄槽实际长度;检测近表面窄槽缺陷应选择少阵元数,远距离检测则应采用多阵元检测。第四,采用相控阵超声斜探头开展了关于航空涡轮盘复杂区域微小缺陷的试验研究,优化相控阵超声检测参数,深入分析航空涡轮盘相控阵超声检测特征信号,结果表明:采用5MHz频率相控阵超声斜探头、激发32阵元、激励信号脉冲宽度设置为100ns、聚焦深度为102mm(孔深)可有效检测该缺陷。最后,为提高航空涡轮盘微小缺陷相控阵超声检测信号的信噪比以及扇扫图像质量,深入分析结构检测信号特征,并采用小波包分解技术观察缺陷检测信号的时频特征,对比了小波阈值及小波基对检测信号降噪效果的影响并对小波包阈值进行优化以获得最优小波包降噪参数。为进一步提高图像质量,采用奇异值分解技术对经小波包处理后的航空涡轮盘超声相控阵检测信号做进一步处理,对比了Hankel矩阵维数如何选取以及奇异值如何处理时的降噪效果,从而得到最优奇异值降噪参数,结果表明:航空涡轮盘中微小缺陷信号紧邻航空涡轮盘结构信号;缺陷特征信号并非集中在某一频带范围内,因此,针对特定频带范围进行滤波将在滤除噪声的同时可能造成缺陷特征信号的损失;根据小波包分析结果选择部分分解信号并结合改进的去噪阈值,可有效的提取检测图像的缺陷特征图像、结构特征图像,甚至也可将材料组织结构引起的噪声条纹提取出来;采用优化参数后的奇异值分解技术对相控阵超声检测数据做进一步处理并成像,缺陷信噪比以及分辨率得到进一步提高。综上,采用相控阵超声检测技术对高温合金航空涡轮盘进行安全、有效的无损检测可保障涡轮盘质量及安全性,在节约制造成本、提高涡轮盘性能、避免安全事故等方面具有重要意义。
[Abstract]:The air turbine disc is the core part of the aero-engine, and due to the fluctuation of process parameters, various defects such as segregation, inclusions, holes, cracks and the like can be caused, the service process is complex in force, and the condition is severe, and the fatigue crack defect is often generated, It is necessary to carry out the non-destructive testing of the air turbine disk in the factory and in-service even if there is a minor defect in the air turbine disk. Phased-array ultrasonic detection technology is a kind of non-destructive testing technology that can realize the variable angle and deep zoom of the acoustic beam through the electronic method, so as to avoid the defect of the conventional single crystal probe caused by the limited moving range and the limited sound beam angle. In addition, the sound field energy control capability of the phased array ultrasonic detection technology is strong, the detection energy is high, and the detection accuracy and the detection efficiency can be effectively improved. According to the characteristics of the phased array ultrasonic detection technology, the phased array ultrasonic detection technology is expected to carry out accurate and high-efficiency nondestructive testing on various defects in the high-temperature alloy aviation turbine disc of the complex structure. The phased array ultrasonic detection technology has the advantages of large volume, complex structure and coarse structure of the tissue structure when the aviation turbine disk is detected by the phased array ultrasonic detection technology, and when the micro defects are located in the near surface, the bottom surface and the complex structure region of the aviation turbine disk, the defect signal is easy to be confused, the signal-to-noise ratio is low, The defect detection is prone to missing or false detection. Therefore, the characteristics of the sound field distribution of the phased array and its influencing factors are analyzed to optimize the detection parameters, the detection signal is analyzed and the corresponding signal processing algorithm is proposed to noise reduction of the detection signal and the image, which is the main research content of the aviation turbine disk phased array ultrasonic detection technology. First, the influence of the parameters of the array element number, the array element distance and the frequency on the ultrasonic sound field of the aviation turbine disk phased array is analyzed. The results show that the energy of the phased array ultrasonic focusing sound field is enhanced with the increase of the number of the array elements and the increase of the frequency. The amplitude of the phased array ultrasonic grating increases with the increase of the array element pitch. Secondly, the characteristics of the ultrasonic phased array sound field in the disk device are analyzed, and the variation of the width of the phased array ultrasonic focal zone and the amplitude of the signal amplitude along with the number of the array elements and the focusing depth is measured. The results show that the width of the phased array ultrasonic focal zone decreases with the increase of the number of the array elements. The effect of the array element number and the position of the probe placement on the detection resolution is analyzed, and the results show that the number of the matrix elements is increased, the proper adjustment of the probe position increases the scan line angle spacing that intersects the cross-hole image to increase the detection resolution. thirdly, the ultrasonic phased array oblique probe is adopted to test the groove type defects in the aviation turbine disc, and the ultrasonic phased array imaging method and the image characteristic of the plane type defect in the aviation turbine disc are analyzed in detail, and the influence of array element number and probe arrangement position on the detection precision of the narrow groove is analyzed, and the result shows that the long value of the phased array ultrasonic measurement is slightly larger than the actual length of the narrow groove; In order to detect the defects of the near-surface narrow groove, the number of elements should be selected, and the multi-array element should be used for long-distance detection. In the fourth part, the experimental research on the micro-defect of the complex area of the aviation turbine disc is carried out by using the phased array ultrasonic oblique probe, and the ultrasonic detection parameters of the phased array are optimized, and the characteristic signals of the phased array ultrasonic detection of the aviation turbine disc are analyzed in detail. The results show that a 5MHz frequency phased array ultrasonic oblique probe is adopted, The excitation signal pulse width is set to 100ns, the focus depth is 102mm (hole depth), and the defect can be effectively detected. in that end, in order to improve the signal-to-noise ratio of the micro-defect phased array ultrasonic detection signal of the aviation turbine disk and the quality of the fan-scan image, the characteristic of the structure detection signal is deeply analyzed, and the time-frequency characteristic of the defect detection signal is observed by using the wavelet packet decomposition technique, The influence of the small wave threshold and the wavelet basis on the noise reduction effect of the detection signal is compared, and the wavelet packet threshold is optimized to obtain the optimal wavelet packet noise reduction parameter. In order to further improve the image quality, the ultrasonic phased array detection signal of the air turbine disk after the wavelet packet processing is further processed by using the singular value decomposition technique, and the noise reduction effect when the Hankel matrix dimension number is selected and the singular value is processed is compared, so as to obtain the optimal singular value noise reduction parameter, according to the wavelet packet analysis result, a partial decomposition signal is selected and combined with the improved de-noising threshold value, the defect characteristic image and the structural characteristic image of the detection image can be effectively extracted, and can even extract the noise fringes caused by the structure of the material, further processing and imaging the phased array ultrasonic detection data by using the singular value decomposition technology after the optimization parameters, and further improving the signal-to-noise ratio and the resolution of the defect. The high-temperature alloy aero-turbine disk is safe and effective by adopting the phased-array ultrasonic detection technology, and the quality and the safety of the turbine disk can be guaranteed, the manufacturing cost is saved, the performance of the turbine disk is improved, safety accidents are avoided, and the like.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：V263.6;TB559

【参考文献】