【作者】 焦标强；

【导师】 史耀武；

【作者基本信息】 北京工业大学 ， 材料加工工程， 2005， 硕士

【摘要】 本研究采用先进的数字信号处理技术,对超声检测原始信号进行变换和处理,试图从超声检测信号中挖掘出可用于表征材料特性的有用信息,达到提高超声检测可靠性的目的。本课题的研究对象是铜-钢异种材料摩擦焊接头和汽车用镀锌钢板点焊接头。在对铜-钢异种材料摩擦焊接头的超声无损检测中,采用聚焦探头水浸法,利用小波分析技术对接头采样点超声A 信号进行消噪及小波包分解,并利用“能量-缺陷”分析方法,对接头质量与接头界面超声反射信号能量分布关系进行研究。调查发现,超声A 信号经小波包变换后,根据各个频带上的能量分布规律可以直接反映出接头局部区域的剪切强度,进一步判断接头的结合质量。在对汽车用镀锌钢板点焊接头的超声无损检测中,采用超声直接接触法提取接头超声A 信号,采用快速傅立叶变换对检测到的超声波A 信号进行变换,分析信号的频域特性。研究表明,高频信号幅度值随焊核直径和接头强度的增加而下降。根据傅立叶变换后高频部分的幅值,不但可以判断镀锌板点焊试样焊核的大小以及试样拉伸强度的高低,而且可以区分虚焊试样和有焊核试样。对铜-钢异种材料摩擦焊接头和汽车用镀锌钢板点焊接头超声检测信号的研究表明,对超声检测过程采用适当的数字信号处理技术可以有效的提高超声检测的可靠性。更多还原

【Abstract】 In the present work the advanced DSP technology has been applied to the transform and processing of signals acquired from ultrasonic non-destructive testing. The purpose is to find useful information from the ultrasonic signal, which can show characteristics of materials. Thus, the reliability of the ultrasonic non-destructive testing may be improved. In this project copper-steel friction-welds and car body’s coated steel spot welds have been studied. In the study of ultrasonic non-destructive test signals for the copper-steel friction-welded joint, immersion method and focusing sensor were used. Wavelet analysis method was used to decrease the noise, and wavelet package analysis method was used to decompose the ultrasonic A-signal. In addition an “energy-defect”analysis method was used to study the relation between the bonding quality and the energy of ultrasonic reflective signal at the joints interface. The results show that the bonding quality and shear strength may be evaluated through energy spectrum distribution from the wavelet package transform of the ultrasonic A signals. In the study of ultrasonic non-destructive test signals for car body coated steel spot -welded joint, direct contacting method was used to pick-up the A-signal. FFT was used to study the characteristics at frequency domain of the ultrasonic signals. It is indicated that the high frequency amplitude of the signals is decreased with the increase of spot size and strength of joints. Through the FFT, the high frequency amplitude of ultrasonic testing signal not only are used to evaluate the spot size and tension strength, but also the specimens with perfect nut can be distinguished from that with poor nut. The study for the ultrasonic testing signal of the two kinds of welded joints shows that proper DSP technology can improve the reliability of ultrasonic testing.更多还原