【作者】 李文强；

【导师】 马福昌；

【作者基本信息】 太原理工大学 ， 电路与系统， 2011， 博士

【摘要】 本文结合超声无损检测的工程现状,分析了一种改进型超声无损检测方法—透射时差法(Time of Flight Transmission,简称TOFT)。在TOFT无损检测方法理论分析的基础上,设计实验系统对石油钻铤管材(材质为4145H钢)和尼龙进行实验,结果证明本方法基本可行性并具有一定工程价值。(1)对传统TOFD衍射时差法超声无损检测方法改进,分析了一种TOFT透射时差法超声无损检测方法。TOFT可用于多种缺陷检测,改善TOFD主要用于焊缝缺陷检测的局限,并可简化检测过程。同时从理论上对超声波在探头、界面和工件中的传播过程、特性进行了定性、定量描述。(2)提出一种改进型电容匹配探头谐振的表达式,可为超声发射电路中核心器件参数的选取提供一种科学依据,并可提高电路发射效率(3)研制出一种改进型超声发射电路。通过单稳态触发电路和微分电路,保证场效应管控制信号的幅值、驱动能力和窄脉冲化；选用导通电阻低的场效应管,缩短导通时间提高电路寿命；利用二极管单向导通性,只允许探头在负电压下工作提高探头寿命；硬件成本未明显提高。(4)研制出一种数字化超声接收调理电路。将固定增益与程控增益有机结合,既实现了增益数字化程控,又保证了电路柔性；增加了噪声抑制电路；数字化程控回波信号的门前沿和门宽。数字化程控降低了操作人员专业知识要求,便于工程应用及系统维护。通过细铜棒超声检测系统2期工程和内六方异型构件超声检测系统的工程应用,证明本超声收发电路具有较高的稳定性和可靠性(5)研制出一种四通道TOFT专用超声采集卡,可实现回波幅值和回波时间测量,可提供数字化增益程控信号、回波的门前沿、门宽程控信号,可为TOFT超声无损检测系统提供一种平台。(6)提出一种改进型中值滤波算法。本算法简单、快速、有效,去除了脉冲噪声、较完整地保留了缺陷信息。实验中,本算法阈值的最大有效范围可达数量级间的变化,表明本算法具有一定的可操作性和工程实用性。更多还原

【Abstract】 This paper analyses an improved ultrasonic testing method called TOFT, time of flight transmission, combining with the engineering situation of ultrasonic nondestructive testing. Firstly, the paper analyzes the theoretical foundation on TOFT. Then, it designs an experiment system and carries out experiments on the drill collar tubing that texture is 4145H steel and nylon respectively. And, the experimental results prove the method is applicable and has some engineering values.(1) It analyses an improved ultrasonic testing method called TOFT, time of flight transmission, based on traditional ultrasonic testing method called TOFD. On one hand, the improved method can used to more testing objects, which breaks the limitation that the traditional TOFD method mainly applies in weld defect testing. On the other hand, it can simplify the testing process. Meanwhile, the paper makes the qualitative and quantitative description on the propagation process and propagation characteristics of ultrasonic in the detector, interface and work piece on theory.(2) It proposes an improved expression that matches the resonance of detector by connecting capacitor in series. The expression provides a scientific basis for parameter selection on core device of the ultrasonic transmitting circuit and improves the transmitting efficiency.(3) It develops an improved ultrasonic transmitting circuit. The circuit ensures the amplitude, drive ability and narrow pulses properties of control signal for MOSFET through monostable trigger circuit and differential circuit. It shortens conduction time and improves the circuit life by choosing the MOSFET that is lower on resistance. It improves lifetime of the detector by utilizing sheet wizard connectivity of the diode to allow the detector works only under negative voltage. However, the hardware cost does not increase obviously.(4) It develops a digital ultrasonic receiving conditioning circuit. The circuit ensures the flexibility and realizes the gain program-controlled by means of combining fixed gain with program-controlled gain. It also adds noise suppression circuit. It can control gate front and gate width of the echo signal through digital and automatic signal. Thus, the automatic regulation can reduce the operators’professional requirement greatly, and can be easy to maintain and engineering application. In addition, the engineering applications of the second phase of ultrasonic testing system for fine copper and ultrasonic testing system for profiled component, prove that the circuit has better stability and reliability.(5) It develops a special TOFT acquisition card which has 4 channels for ultrasonic testing. The card can measure echo’s amplitude and time and provide program-controlled signals on gain, program-controlled signals on gate front and gate width. Thus we can say that it can provide a kind of platform for ultrasonic testing system based on TOFT method.(6) It proposes an improved median filtering algorithm. The algorithm is simple, fast and effective. It removes the noise and retains the defect information relatively complete. The maximal ranges about valid threshold between orders of magnitude on trial, so it improves engineering practicability and operability for the algorithm.更多还原