共查询到19条相似文献,搜索用时 859 毫秒
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为解决应用超声导波检出油气对焊弯管缺陷的难题,分析了弯头及环焊缝对L(0,2)模态、T(0,1)模态导波的传播影响,发现环焊缝会使导波产生反射,弯头及环焊缝会使导波产生衰减和模态转换,而导致油气对焊弯管缺陷难以检出;提出了基于B扫描成像的超声导波检测方法,通过B扫描图像辅助识别弯管缺陷信号;最后加工了2根带缺陷的油气对焊弯管,采用上述方法进行检测试验。试验结果表明,基于B扫描成像的超声导波检测方法能够有效检测并定位出弯头及过弯头后直管上的缺陷。 相似文献
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《无损检测》2019,(12)
超声导波在弯管中的传播较在直管中人传播更为复杂,而在实际工程现场,弯管弯头部位的检测尤为重要。利用磁致伸缩超声导波激励出扭转模态T(0,1),研究了超声导波在弯管中典型部位的缺陷检测问题及不同检测频率对弯管缺陷识别的影响。试验结果表明:检测频率低会导致超声导波反射信号在拱背外侧缺陷和弯头焊缝处发生频散而难以分离;检测频率高,得到的弯头拱背内侧缺陷与拱背外侧缺陷的信号幅值都很小。因此选择合适的检测频率,才能更好地对弯头缺陷进行有效识别。T(0,1)模态导波经过弯头时,能量会在拱背外侧产生聚焦,在拱背内侧出现发散,拱背外侧缺陷比拱背内侧缺陷更容易检出;信号经过弯头后,能量衰减严重,衰减后的能量约为原来的一半。 相似文献
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首先进行了超声导波的理论分析,并且应用有限元分析软件建立了钢筋超声导波传播模型,进行了钢筋不同缺陷长度和深度超声导波传播数值模拟。其次,基于钢筋缺陷损伤回波信号,研究了其反射系数与回波时间,得到了钢筋在不同损伤程度下的超声导波传播规律,并给出了缺陷的位置及影响因素。最后,对模拟信号进行时频分析,验证了超声导波检测的准确性。 相似文献
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基于ANSYS二次开发的三维金属成形数值模拟研究 总被引:3,自引:0,他引:3
本文在ANSYS平台上,利用其固有的参数化设计语言APDL和用户编程特性UPFs进行二次开发,实现了金属成形三维数值模拟分析的网格重划功能,并通过实验证明了二次开发的正确性。 相似文献
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Local wall thinning of pipes, resulting from corrosion, is the major cause of accidents in nuclear power plants. In order to assure the integrity of pipes, a variety of NDE techniques have been proposed. It is well recognized that the utilization of guided waves to detect flaws in pipes has been a very effective tool for long-range inspection in NDE. Since most conventional research on guided waves has focused on long-range inspection, it is difficult to evaluate a defect in a local area. An objective of this study is to develop a non-contact inspection technique for the quantitative evaluation of defects on a local area in a cylindrical tube. Therefore, the purpose of this study is to introduce an advanced inspection system and a new signal processing method for the evaluation of defects such as corrosion in a pipe. In this study, an advanced non-contact method for pipe inspection is proposed, which generates the ultrasonic guided wave by laser and receives it by a dual air-coupled transducer. Information on each directional defect location and length is obtained by using a line scan along a circumferential and longitudinal direction. Received signals are analyzed by using the peak-to-peak amplitude of waveform and the maximum center frequency magnitude of the frequency spectrum. The optimal mode selection of guided waves based on a dispersion curve is also discussed. The experimental results using the proposed method show that the location and the size of the defect could be evaluated successfully in the 2-dimensional scanning images. 相似文献
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There is an increasing interest in high frequency short range guided waves to screen or monitor for corrosion. This contrasts with long range guided waves (LRGWs) which screen pipes for large patches of corrosion and have been successfully used in corrosion management for the past twenty years. The fundamental setup described in this paper uses circumferential guided waves, which are excited at a single location on a pipe and travel around the pipe wall and are detected at the same location. The study uses a finite element model assisted method to evaluate the detection capability of two short range circumferential guided wave setups which use both the reflected and transmitted signals. The setups themselves consist of either an axial array of transducers, for monitoring, or a single transducer which axially scans a pipe. Both setups have an array or scan pitch between either adjacent transducers or measurements. The detection capability of the fundamental Lamb wave modes (A0 and S0) in both reflection and transmission have been compared, as well as a hybrid shear horizontal wave setup, which uses the SH0 mode in reflection and the SH1 mode in transmission. A sensitivity analysis was conducted using two separate methods to determine the probability of detection (POD) for either the reflection or transmission signals. Both methods determine a POD for a specific defect, noise level, and array or scan pitch. Probability images are produced which map the POD for a range of defect sizes. For the parameters investigated in this study, it was found that in transmission large diameter defects have a higher detectability, whereas deep, narrow diameter defects are more detectable in reflection. A generalised overview of the sensitivity of short range guided waves is presented by combining both the reflection and transmission PODs. The data fused sensitivity of the S0 and SH hybrid modes are given as 0.6% and 0.75% cross sectional area (CSA) respectively, allowing for the comparison with LRGWs. The A0 mode was excluded from the POD analysis because it was much less sensitive than the other two modes. 相似文献
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A time–frequency signal processing procedure aimed at extending pulse-echo defect detection methods based on guided waves to irregular waveguides is proposed. In particular, the procedure returns the distance traveled by a guided wave that has propagated along a waveguide composed by segments with different dispersive properties by processing the detected echo signal. To such aim, the acquired signal is processed by means of a two-step procedure. First, a warped frequency transform (WFT) is used to compensate the dispersion of the guided wave due to the traveled distance in a portion of the waveguide that is assumed as reference. Next, a further compensation is applied to remove from the warped signal the group delay introduced by the remaining irregular portion of the waveguide. Thanks to this processing strategy, the actual distance traveled by the wave in the regular portion of the irregular waveguide is revealed. Thus, the proposed procedure is suitable for automatically locate defect-induced reflections in irregular waveguides and can be easily implemented in real applications for structural health monitoring purposes. The potential of the procedure is demonstrated and validated numerically by simulating and processing Lamb waves propagating in waveguides made up of different uniform, tapered and curved segments. 相似文献