碳纤维复合材料表面雷达吸波涂层超声测厚方法研究

针对碳纤维复合材料基底表面涂覆的雷达吸波涂层在超声测厚过程中由于涂层与基底间声阻抗接近导致界面回波信号弱,手动读取脉冲回波声程差时主观性强、效率低的问题,提出一种基于理论分析结合Matlab批量信号处理技术的涂层厚度测量方法.理论分析确定涂层上下表面回波信号的相位变化关系;采用Matlab脚本批量读取超声脉冲回波信号,...     

基于频率—相位编码信号激励的焊缝超声检测分析

焊接结构在工业领域的应用十分广泛,常应用于复杂结构中,对焊接质量要求较高,需要高时间分辨率的超声检测方法检测焊缝内部缺陷.为了提高检测结果的时间分辨率,将雷达领域的编码激励与脉冲压缩技术引入焊缝检测中,提出一种基于幅度加权频率调制的相位编码激励检测方法,该方法的激励信号为幅度加权的线性调频信号与巴克码信号的复合.结果表明,相同带宽下,与线性调频信号和巴克码激励的检测结果相比,所提出的激励方法检测结果的时间分辨率较高,同时,有效降低了调频带宽对检测结果的影响.     

钢板缺陷的脉冲漏磁检测系统设计及试验

基于脉冲漏磁检测技术检测钢板缺陷,实现钢板表面和背面缺陷的区分。利用设计的钢板脉冲漏磁检测系统,提取了钢板表面和背面缺陷的信号,分析在脉冲信号激励下的缺陷漏磁信号特征。根据信号电压峰值和电压谷值同步曲线区分缺陷,编写了基于Labview的检测程序,实现了钢板表面和背面缺陷检测和区分。在实验室条件下,通过设计的脉冲漏磁检测系统,对刻有矩形槽的钢板进行了检测。试验结果表明,基于脉冲漏磁检测技术,利用电压信号峰值和谷值同步采样曲线,可对钢板表面和背面缺陷进行检测和区分。     

敫励参数和试件电磁参数对脉冲涡流检测影响的仿真分析

脉冲涡流检测技术已成功应用于带包覆层容器和管道壁厚检测。然而,由于铁磁性材料脉冲涡流检测机理的复杂性,目前缺乏对检测信号影响因素的有效分析方法。首先利用有限元仿真方法建立了脉冲涡流检测模型,并用试验验证了模型的正确性;然后研究了重复频率、占空比及边沿斜率等激励参数对检测信号的影响,为脉冲涡流检测激励模式的选择提供参考;最后分析了试件电磁参数对检测信号的影响,为脉冲涡流检测结果的解释提供依据。     

在役奥氏体不锈钢螺栓的超声相控阵检测

针对在役奥氏体不锈钢螺栓可靠性检测的需要,仿真分析了超声相控阵在奥氏体不锈钢螺栓中的声场分布情况,观察超声相控阵声场在奥氏体不锈钢螺栓中的覆盖范围,并通过设定检测工艺参数,仿真分析比较在役奥氏体不锈钢螺栓在完好状态和有缺陷时的声场回波情况。在奥氏体不锈钢螺栓相控阵声场仿真计算的基础上,讨论分析不同脉冲重复频率对检测结果准确性的影响,并给出如何消除脉冲重复频率产生的幻影回波伪缺陷信号的方法;最后结合仿真计算和脉冲重复频率工艺优化方法,应用超声相控阵方法成功检测出含裂纹缺陷的在役奥氏体不锈钢螺栓,验证了在役奥氏体不锈钢螺栓超声相控阵检测工艺的准确性。     

脉冲反射法检测粘接缺陷的有限元模拟

为深入理解工件内脱粘状态与检测回波信号间的关联,使用有限元模拟技术对超声脉冲反射法检测粘接缺陷的工艺参数进行了计算分析。对超声检测时的激励信号进行了定量描述,经采样后将其作为位移载荷加载于探头区域内。首先对良好粘接工件,计算了探头接收到的检测回波信号;然后使用窄脉宽信号进行再次分析;最后,对工件中存在不同尺寸的脱粘情况进行了计算,将检测回波信号进行了对照分析。有限元模拟结果表明:使用脉冲反射法对钢铅两层金属间较薄的粘接层进行检测时,需要有效提高探头的分辨力,以识别出钢层一次与二次回波间的粘接层回波信号,使用此信号幅值可定量反映脱粘大小。     

脉冲涡流检测系统影响因素分析

脉冲涡流检测系统中参数的选择对于提高缺陷的检测灵敏度具有重要的意义。分析了激励线圈的尺寸、激励脉冲的频率、占空比和电压等因素对脉冲涡流检测系统的影响,给出了实际检测过程中选择参数的原则。     

超声热成像检测应用实例

简要介绍了超声热成像检测方法的基本原理和特点。该方法利用激励超声波在缺陷处产生机械振动,使缺陷处因热弹效应和滞后效应等原因释放出热量,用红外热像仪对此局部发热过程进行监测,最后对图像进行分析。由于激励信号的频率调制和特殊的图像处理方法,超声热成像检测法优势独特。对某航空碳纤维增强复合材料的检测表明,该方法能有效检测出裂纹、分层或破裂等缺陷,应用前景广阔。     

一种基于DDS技术的脉冲涡流信号源的实现

脉冲涡流检测技术是近几年新兴的无损检测方法。与传统涡流检测法不同,它以一定占空比的方波脉冲为激励,此信号经过傅里叶变换可分解为无限多个谐波分量之和,所以在采集的磁场信号中含有更多信息。根据脉冲涡流检测法自身的特点,基于DDS技术,设计了一种参数可调式脉冲波形发生器。通过试验验证,此波形发生器性能稳定、参数设置方便,能满足涡流检测系统激励信号的要求,有很好的推广应用价值。     

LFM激励信号在超声TOFD检测中的应用

对于大厚度焊接试件的超声衍射时差法检测(time of flight diffraction, TOFD),常规超声激励难以同时满足信噪比、检测距离以及检测分辨率的要求.文中将线性调频脉冲压缩技术应用在超声TOFD检测中,线性调频(linear frequency modulated, LFM)激励可综合改善检测信噪比(signal to noise ratio, SNR)与分辨率.首先对试验用10 MHz超声换能器进行了LFM信号参数测试,选择了合适的时宽和带宽.对埋藏3 mm高的横槽缺陷的钢板分别进行了超声LFM激励的TOFD检测及常规超声TOFD检测,对比发现超声LFM激励的TOFD检测精度高达0.01μs,可准确区分缺陷上下端衍射波.在较低的激励电压和系统增益下,实现了较高的检测信噪比及分辨率.     

基于电磁超声的钢板裂纹检测系统

设计了一种基于磁致伸缩原理的电磁超声裂纹检测系统。该系统由脉冲电源激励换能器线圈,进而在钢板中激发超声波,接收信号经过放大滤波后输入计算机进行处理。利用此系统进行钢板裂纹检测试验,裂纹定位误差〈1％。系统运行稳定可靠,可以用来检测钢板裂纹缺陷。     

棒材中超声散射场的模拟及信号的识别

棒材是一种应用很广泛的型材,因此棒材的无损检测十分重要。提出一种脉冲超声场模拟的方法,模拟了玻璃棒中的超声波散射声场。通过与动态光弹实验结果比较,解释了圆棒的超声检测中散射波（如瑞利波）的形成机理。在此基础上,用单换能器采集圆棒中的连续回波信号并对信号做相关处理,仅需测量一次棒材的回波信号就可以计算其力学性能结果。该方法对棒材探伤和力学性能评价等方面有很大用途。     

超声检测中的声场特性及应用分析

针对超声检测中影响缺陷定量准确性的声场问题进行了深入讨论，研究了脉冲波声场的计算方法，绘制出实用换能器声轴线上的声压分布曲线，分析了不同材料和厚度的采样回波对频谱的影响，比较了连续波声场和脉冲波声场的分布特性及异同点，为提高超声检测中缺陷定量的准确性和科学性提供了依据。     

PZT激励同步压缩放电通道微细电火花加工工艺参数对加工结果的影响

提出了压电陶瓷(piezoelectric ceramic transducer,PZT)激励同步压缩放电通道微细电火花加工,目的在于改善微细电火花加工的放电环境。介绍了PZT激励同步压缩放电通道微细电火花加工原理,研究了开路电压、脉冲宽度、脉冲频率和峰值电流对其电极损耗和材料去除率的影响,并与不采用压缩通道方法的微细电火花加工进行了对比。结果表明:同等条件下,采用PZT激励同步压缩放电通道技术,提高了加工过程的稳定性和材料去除率,降低了电极损耗率,有效改善了放电环境。     

Thickness measurement approach for plasma sprayed coatings using ultrasonic testing technique

The special ultrasonic testing system has been developed for thickness measurement of plasma sprayed coatings. The ultrasonic immersion method was used to obtain stable coupling condition and avoid other disadvantages of contact method. Spherical acoustic lens were designed to focus ultrasonic beam so as to improve beam directivity and concentrate ultrasonic energy. To increase testing precision and avoid mussy wave signals, moderate pulse width and frequency of the transducer has been selected. The displacement of transducer in X-Y-Z directions was precisely manipulated by step-controlled system to insure the accuracy of focus length and repetition of measurement. Optimized testing conditions (with the transducer of center frequency of 10 MHz and crystal diameter of 8 mm, focus length of 9.5 mm, diameter of focal column of 0. 1 mm and length of focal column of 0.27 mm) were selected to determine the thickness between 285 -414 μm of ZrO2 coatings plasma sprayed on the nickel based superalloy. The frequency interval of the periodic extremums in ultrasonic power spectra decreases with increasing coating thickness. The ultrasonic results accord with those of metallographical method.     

空气耦合式超声检测在航空无损检测中的应用

针对复合材料的无损检测问题,探讨了一种基于穿透式异侧检测模式的空气耦合式超声波检测技术,阐述了该技术的基本原理。参照传统的液浸式超声波检测技术,以航空工业中重要的γ-TiAl基合金为研究对象,对检测过程中信号的衰减与损耗进行了详细的理论分析与数值计算。结果表明,超声波在介质交界面处的反射损耗和在空气中的传输衰减是目前空气耦合式超声检测技术应用遇到的主要难题,而研制新型超声波换能器是解决问题的关键。     

New matching pursuit-based algorithm for SNR improvement in ultrasonic NDT

In this paper a fast and efficient matching pursuit-based algorithm is proposed for SNR improvement in ultrasonic NDT of highly scattering materials. The proposed algorithm utilizes time-shifted Morlet functions as dictionary elements because they are well matched with the ultrasonic pulse echoes obtained from the transducer used in the experiments. The proposed algorithm is fast enough to be used in the signal processing stage of real time inspection systems. Computer simulation has been performed to verify the SNR improvement for diverse ultrasonic waves embodied in high-level synthetic grain noise. This improvement is also experimentally verified using ultrasonic traces acquired from a carbon fibre reinforced plastic material. Numerical results show meaningful SNR improvements for low input SNR ratios (below 0 dB).     

Improvement of ultrasonic testing of concrete by combining signal conditioning methods, scanning laser vibrometer and space averaging techniques

This paper deals with the combination of several techniques to improve the ultrasonic pulse echo testing of concrete elements when a laser doppler interferometer is used as the ultrasonic receiver. This techniques involves specially designed ultrasonic probes, a pulse compression technique, random speckle modulation and space time signal processing methods. The pulse echo technique is carried out by sending frequency modulated chirp signals and performing a cross-correlation between the received and the transmitted signals. In combination with the application of recently available ultrasonic concrete probes as transmitter, this leads to an improvement in the signal-to-noise ratio. A laser doppler interferometer, equipped with a random speckle modulator, is used as detector of the ultrasound. Finally, the data sets are processed with various methods, involving time signals of several space points. Examples are the space averaging and the synthetic aperture focusing technique (SAFT). The advantage of the suggested technique is demonstrated by practical measurements on a test specimen. The improvement in results as compared to standard laser interferometric measurements will increase the feasibility of laser interferometric detection for non-destructive testing in civil engineering.