When the high frequency focused ultrasound technology is used to detect internal defects in metal materials, the defects near the surface can’t be accurately located due to the blind zone. Thus it is difficult to evaluate the performance of the material. Therefore, the method of the defect feature extraction in ultrasonic blind zone based on mathematical morphology is proposed. Firstly, signal of the blind zone is processed by morphological filter via the flat structure element, so the characteristic signal of the defect is extracted. After that, the accumulated energy of the characteristic signal is calculated, which can be used to locate the depth of the defect. In the experiment, the cold rolled galvanized sheet is detected using a high frequency focused ultrasonic transducer of 100 MHz. The ultrasonic signal is processed with morphological filter via the flat structuring elements with length of 30. The distance between the defect and the surface of the material is 288.5 μm, and the position of the defect is 275.6 μm determined by the proposed method, so the relative error of the defect position is 4.5%. In order to verify the effectiveness of the method, wavelet packet method is compared. The results show that the method of mathematical morphology has smaller error and improves the B-scan imaging effect. So the defect feature can be more obvious.
LI Min
,
SONG Yanan
,
ZHOU Tong
,
XU Jinwu
. Defect Feature Extraction in Ultrasonic Blind Zone Based on Mathematical Morphology[J]. Journal of Mechanical Engineering, 2016
, 52(12)
: 16
-22
.
DOI: 10.3901/JME.2016.12.016
[1] ASTM International USA. E1065. Standard practice for evaluating characteristics of ultrasonic search units[S]. West Conshohocken：ASTM International.,2014.
[2] 刘松平,刘菲菲,史俊伟,等. 复合材料冲击损伤高分辨率超声成像检测与损伤行为分析[J]. 机械工程学报,2013,49(22)：16-23.
LIU Songping,LIU Feifei,SHI Junwei,et al. High-resolution ultrasonic imaging evaluation and behavior analysis of impact damages in composites[J]. Journal of Mechanical Engineering,2013,49(22)：16-23.
[3] 齐飞,陈晶晶,王润田. 反相叠加减小超声检测盲区的方法[J]. 声学技术,2011,30(4)：325-329.
QI Fei,CHEN Jingjing,WANG Runtian. The opposite phase superposition method of decreasing blind zone in ultrasonic detection[J]. Technical Acoustics,2011,30(4)：325-329.
[4] HERNÁNDEZ Á,UREÑA J,MAZO M,et al. Reduction of blind zone in ultrasonic transmitter/receiver transducers[J]. Sensors and Actuators A：Physical,2007,133(1)：96-103.
[5] DRAI R,SELLIDJ F,KHELIL M,et al. Elaboration of some signal processing algorithms in ultrasonic techniques：Application to materials NDT[J]. Ultrasonics,2000,38(1)：503-507.
[6] 魏东,周正干. 改进的非线性调频脉冲压缩方法在空气耦合超声检测中的应用[J]. 机械工程学报,2012,48(16)：8-13.
WEI Dong,ZHOU Zhenggan. Application of non-linear frequency-modulation based pulse compression in air-coupled ultrasonic testing[J]. Journal of Mechanical Engineering,2012,48(16)：8-13.
[7] BETTAYEB F,HACIANE S,AOUDIA S. Improving the time resolution and signal noise ratio of ultrasonic testing of welds by the wavelet packet[J]. NDT & E International,2005,38(6)：478-484.
[8] FRITSCH C,VECA A. Detecting small flaws near the interface in pulse-echo[J]. Ultrasonics,2004,42(1)：797-801.
[9] SONG Shoupeng. A new signal processing technique for detecting flaw echoes close to the material surface in ultrasonic NDT[J]. Russian Journal of Nondestructive Testing,2010,46(1)：69-74.
[10] ZHANG Guangming,HARVEY D M,BRADEN D R. Effect of sparse basis selection on ultrasonic signal representation[J]. Ultrasonics,2006,45(1)：82-91.
[11] LI Xiang,LI Xunbo,LIANG Wei,et al. l0 -norm regularized minimum entropy deconvolution for ultrasonic NDT & E[J]. NDT & E International,2012,47(1)：80-87.
[12] 张树潇,谢雪,刘丽丽,等. 基于频谱分析原理减小TOFD检测近表面盲区的方法[J]. 无损探伤,2014,37(6)：20-26.
ZHANG Shuxiao,XIE Xue,LIU Lili,et al. The method on reducing the TOFD on blind field near the detected surface based on spectrum analysis[J]. NDT,2014,37(6)：20-26.
[13] 曾纪勇,丁洪发,段献忠. 基于数学形态学的谐波检测与电能质量扰动定位方法[J]. 中国电机工程学报,2005,25(21)：57-61.
ZENG Jiyong,DING Hongfa,DUAN Xianzhong. Harmonics detection and disturbance location methods based on mathematical morphology[J]. Proceedings of the CSEE,2005,25(21)：57-61.
[14] 梁仲刚,王勤,严宏. 航天飞行中心电信号去噪方法研究[J]. 航天医学与医学工程,2006,19(5)：354-357.
LIANG Zhonggang,WANG Qin,YAN Hong. Research on ECG denoising during spaceflight[J]. Space Medicine & Medical Engineering,2006,19(5)：354-357.
[15] 赵晓群,刘颖娜,伍睿. 基于形态滤波的基音检测新方法[J]. 通信学报,2004,25(5)：53-58.
ZHAO Xiaoqun,LIU Yingna,WU Rui. A new approach of pitch detection based on morphology filter[J]. Journal of China Institute of Communications,2004,25(5)：53-58.
[16] 章立军,杨德斌,徐金梧,等. 基于数学形态滤波的齿轮故障特征提取方法[J]. 机械工程学报,2007,43(2)：71-75.
ZHANG Lijun,YANG Debin,XU Jinwu,et al. Approach to extracting gear fault feature based on mathematical morphological filtering[J]. Chinese Journal of Mechanical Engineering,2007,43(2)：71-75.
[17] 杨杰,郑海起,刘晓平,等. 多尺度柔性形态滤波在轴承故障诊断中的应用[J]. 轴承,2011(3)：41-44.
YANG Jie,ZHENG Haiqi,LIU Xiaoping,et al. Application of multi-scale soft morphological filter in fault diagnosis of bearings[J]. Bearing,2011(3)：41-44.
[18] 胡爱军,向玲,唐贵基,等. 基于数学形态变换的转子故障特征提取方法[J]. 机械工程学报,2011,47(23)：92-96.
HU Aijun,XIANG Ling,TANG Guiji,et al. Fault feature extracting method of rotating machinery based on mathematical morphology[J]. Journal of Mechanical Engineering,2011,47(23)：92-96.
