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排序方式: 共有90条查询结果,搜索用时 15 毫秒
1.
Austenitic welds are inspected using PPM EMAT generated shear horizontal (SH) waves. Results are compared to measurements taken using a 1D piezoelectric phased array using the total focusing method (TFM). For the first time there is clear experimental evidence of the SH wave method demonstrating higher sensitivity to defect detection. SH waves suffer less beam steering in a weld than either compression or SV waves, which can miss defects due to weld microstructure anisotropy and attenuation. All defects were identified from every side of the weld/plate using the SH waves, but this was not possible using the piezoelectric transducer. 相似文献
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Beam steering has been achieved using shear horizontal waves generated using a periodic permanent magnet (PPM) electromagnetic transducer (EMAT). Unlike phased arrays, where steering is achieved by carefully controlling the firing of individual elements, the spatial periodicity of the PPM EMAT is ultilised to steer the beam whilst exciting all elements simultaneously. Due to the periodic nature of the array, the interference of individual waves from each of the elements creates a highly frequency dependent angle of propagation, allowing the directivity to be changed by simply varying the frequency of the input signal. Simultaneous excitation precludes the need for complicated and expensive phased array hardware. A frequency domain model is developed so that the beam characteristics, such as steering angle and beam width, can be calculated, allowing for investigation into the beam steering qualities of the PPM transducer. Broadband pulsed generation is also demonstrated, showing how a wave is generated over a large range of angles, meaning a large area can be covered with a single pulse. Interesting properties of this wave, such as a variation of frequency as a function of angle, and how this can be useful, are also discussed. 相似文献
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We present recent work on a dual probe system containing electromagnetic acoustic transducers (EMATs) generating and detecting surface ultrasonic waves, and a pulsed eddy current (PEC) probe. This system is able to detect and size surface and near-surface defects in electrically conducting samples by looking at changes in the detected signal for each probe. By combining the information from each probe using a weighted logic function for data fusion, it is possible to both classify and size defects, with increased reliability. By combining the data in this way one obtains information about the defects which is not available when using either probe in isolation. Typical results on steel and aluminium samples are presented, along with information about the data fusion function. The dual probe and data fusion routine has been demonstrated to work at manual-scanning speeds, with higher speeds possible following some simple improvements to the system. 相似文献
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弹性层中的SH板波传播特性及电磁超声激励方法的研究 总被引:1,自引:0,他引:1
研究水平剪切波(Shear Horizontal,简称SH波)的传播特性及激励接收方法对该波在无损检测和声弹性技术范围内的工程应用有着重要的价值.首先,SH波在弹性层中传播的多模态、频散特性在文中作了详细的分析,同时重点研究了电磁超声技术在非铁磁性材料波导中产生SH波的探头结构和基础理论,并以试验的方法验证了其部分电声特性,结果表明,SH板波具有其他类型波所没有的独特特性,而电磁超声技术在SH波的激励接收方面有着很大的优势. 相似文献
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电磁声传感器能够非接触地在金属材料中产生和探测超声波,由于不需耦合剂,使得它能够用于高温、高速和粗糙表面这些常规检测方法难以胜任的场合。介绍了所研制的表面波电磁声传感器的工作原理和进行驻波试验的部分结果分析。 相似文献
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R. Bruce Thompson 《Journal of Nondestructive Evaluation》1980,1(2):79-85
An analysis of the radiation from a body force shows that it is equivalent to the radiation from a series of surface stresses defined by the moments of the body force taken with respect to the depth coordinate. As the body force becomes localized near the surface, the zeroth moment of the force dominates the radiation and is often thought of as an equivalent surface stress. However, under certain conditions, this can vanish, and the other moments must be considered. It is found that, as the order of the moment of a particular force component increases, the resulting radiation patterns alternate between those characteristic of a compressive surface stress and those characteristic of a shear surface stress, which have considerably different angular variations. Results of experiments in the development of EMAT transducers for nondestructive testing that support these results are cited, and important consequences in the design of inspection systems are indicated. 相似文献
10.
电磁超声表面波被广泛用来检测表面或近表面缺陷。双向表面波电磁超声换能器(ElectromagneticAcoustic Transducer, EMAT)会在两侧同时产生能量较低且均衡的超声波,而微小缺陷(缺陷深度远小于表面波波长)的反射信号非常微弱,易被噪声淹没,根据回波信号,难以识别和定位缺陷。为此基于惠更斯叠加原理设计了单向表面波EMAT,对其声场进行了有限元分析;研究了增强侧表面波遇到不同缺陷的响应特性,得出缺陷深度、角度与反射波幅值的关系;并对含不同微小缺陷的铝板进行了实验研究。仿真和实验结果表明,所提方法提高了表面波检测微小缺陷的灵敏度,并实现了缺陷位置及深度的量化。 相似文献