共查询到20条相似文献,搜索用时 15 毫秒
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This paper describes a calibration method for acoustic emission and ultrasonic sensors that is effective from 1 kHz to 1 MHz. The method combines generalized ray theory and finite element analysis to model wave propagation at higher and lower frequencies, respectively. A ball impact is used as a calibration source, a thick aluminum plate is used as the test block, and hot glue is used as the couplant. We demonstrate this method on five commercial piezoelectric sensors: Physical Acoustics (PAC) R15a, PAC WSa, Panametrics V101, Panametrics V103, and Valpey-Fisher Pinducer. Our calibration results show that reflections and other wave phases can be more clearly identified with the less-resonant Panametrics sensors. The PAC sensors have the greatest sensitivity and are able to detect surface normal displacements at least down to 1 pm amplitude in the 100s of kHz frequency band. Aperture effect is minimized by the small size of the Pinducer. Our method focuses on the amplitude response of the sensors (phase is ignored) and extends the calibration to a frequency band that is lower than typical analyses. Low frequency information is useful for determining the seismic moment of a seismic source (analogous to the magnitude of an earthquake) and can increase the amount of information acquired in a single recording. 相似文献
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S. O. Gade U. Weiss M. A. Peter M. G. R. Sause 《Journal of Nondestructive Evaluation》2014,33(4):711-723
Electromagnetic emission (EME) testing and acoustic emission (AE) testing are applied to investigate the failure of a brittle, dielectric material under mechanical load. A setup for three point flexure tests comprising simultaneous monitoring of EME and AE was used to induce fracture of epoxy resin specimens. The influences of the orientation and the distance of the crack surface on the detectable EME signals are the subjects of investigation. As EME sensor a capacitive sensor was used. Tests with an artificial test source are carried out to characterize the system response of the sensor, the attached amplifier and acquisition cards as well as the included bandpass filters. We propose an EME source based on the surface charge density modelled at the position of the fracture plane. Results of finite element method modelling of the EME source are compared to experimental results and show very good agreement. The experimental results show a clear directional character of the emitted electromagnetic field and a strong dependence of the detected signals amplitude on source-sensor distance. A significant influence of the measurement chain on the detected electromagnetic signals bandwidth was found. Furthermore it is shown that the electromagnetic signals consist of three contributions originating from different source mechanisms. These are attributed to the separation and relaxation of charges during crack growth and to the vibration of the charged crack surfaces. 相似文献
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声发射检测过程中,对缺陷的定位是重要的一个步骤,传统的声发射检测利用时差定位方法,而时差定位里重要的参数是声速。通过推导,得到一种利用声衰减特性和能量参数对声发射源进行定位的新方法,并用声发射仪对普通钢件以铅笔芯折断作为模拟源进行测试,证明这种无需声速测量的新方法可行,且准确性可以得到保证。该方法的提出为声发射定位技术拓展了新方向,对提高声发射检测质量有一定的帮助。 相似文献
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Changjiang Zhou 《Research in Nondestructive Evaluation》2014,25(1):1-19
This article deals with near-field acoustic emission (AE) signal sensing with a low-profile piezoelectric film strain sensor. In general, AE signals can be represented as a summation of moment tensor (dipoles or double couples) weighted Greens’ functions. Basic theories of the Green's function and moment tensor are introduced first. The formulation presented here extends the AE elastodynamic solution to stress-wave induced surface strain response in half space. As a special case with potential use for sensor calibration, stress wave-induced surface strain response to a surface pulse load is presented. To verify the derivation, experiments were carried out with glass capillary breakage on a large steel block. The experimental result matches the theoretical prediction fairly well. Based on the surface pulse case study, the characteristics of strain and displacement signals are illustrated for both P and Rayleigh wave arrivals, which could provide insights for such strain sensor design and implementation. Due to the finite sensing area of piezoelectric film strain sensor, its aperture effect cannot be neglected in practical use, especially in higher frequency AE signal sensing, which is also investigated in this article. 相似文献
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The paper is concerned with damage accumulation monitored by acoustic emission (AE) techniques during monotonic four-point bending tests on Douglas fir, oak and beech beams. The purpose of the study was to discriminate between the AE responses of the different materials by elementary analysis of ring-down cumulative counting. It appears that this simple method gives results that are species-dependent; in particular, high emission rates were found, to be typical of oak samples. The acoustic emission results are related to the observed structural mechanisms of failure of Douglas fir specimens tested in the radial or tangential directions. 相似文献
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Sridhar Canumalla R. N. Pangborn B. R. Tittmann J. C. Conway Jr. 《Composites Science and Technology》1994,52(4):607-614
The attractive elevated-temperature properties of metal-matrix composities (MMCs) have not been exploited in commercial applications partly because of the high processing cost and lack of reliability in fabrication. In this exploratory study, the feasibility of using acoustic emission (AE) as an in-process, non-destructive quality control technique is examined. A variation of the squeeze casting technique is selected for investigation. Acoustic emission is employed with the intent of non-intrusively establishing whether complete infiltration has occurred during composite fabrication. The problems due to the background noise during AE monitoring are overcome by using transducers with different frequency responses. The acoustic signatures of machine noise, preform crushing and metal solidification are obtained by employing suitable transducers in a series of tests that systematically evaluate the individual processes that comprise infiltration casting. The results form a strong basis for the development of an in situ AE sensor for the infiltration process. 相似文献
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One of the current challenges in health monitoring of composite materials is the use of acoustic emission to identify damage modes. Many classification procedures have been reported in the literature but none of them clearly state limitations to their applicability, making it difficult to quantify them in different testing conditions. In the present paper, a method is described to characterize energy attenuation and how it affects AE signals features based solely on AE signals recorded during mechanical tests. Limitations to damage identification based on AE signals features can therefore be defined. The method is demonstrated on AE signals recorded during tensile tests on four different layups of carbon fiber reinforced polymer composites using signals frequency centroids to describe AE sources. 相似文献
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Four point bend tests were conducted on two previously characterized particulate filled thermoplastic and thermoset polymeric coatings, the acoustic emission (AE) method being utilized to monitor the damage progress during the tests. Different damage mechanisms operating in the polymeric coatings can be recognized by the different amplitude range of the AE signals emitted. AE can be used to assess the relative strength of particle/matrix bonds in particulate filled polymeric coatings. 相似文献
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With the increased utilization of advanced composites in strategic industries, the concept of Structural Health Monitoring
(SHM) with its inherent advantages is gaining ground over the conventional methods of NDE and NDI. The most attractive feature
of this concept is on-line evaluation using embedded sensors. Consequently, development of methodologies with identification
of appropriate sensors such as PVDF films becomes the key for exploiting the new concept. And, of the methods used for on-line
evaluation acoustic emission has been most effective. Thus, Acoustic Emission (AE) generated during static tensile loading
of glass fiber reinforced plastic composites was monitored using a Polyvinylidene fluoride (PVDF) film sensor. The frequency
response of the film sensor was obtained with pencil lead breakage tests to choose the appropriate band of operation. The
specimen considered for the experiments were chosen to characterize the differences in the operation of the failure mechanisms
through AE parametric analysis. The results of the investigations can be characterized using AE parameter indicating that
a PVDF film sensor was effective as an AE sensor used in structural health monitoring on-line. 相似文献
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C. K. Mukhopadhyay S. Venugopal T. Jayakumar S. L. Mannan Baldev Raj B. Chatterji R. Srinivasan V. Gopalakrishnan G. Madhusudan R. S. Tripathi 《Materials and Manufacturing Processes》2006,21(5):543-549
Optimization of a sensor location for effective characterization of a hot forging process using acoustic emission (AE) signals is discussed in this paper. Acoustic emission signals generated during forging operations on an aluminium alloy were recorded using three sensors simultaneously by mounting them on the top bolster, bottom bolster, and bottom die of the press. The AE signals with maximum sensitivity could be detected with a sensor attached to the bottom die in preference to the other positions. Using AE parameters, the forging process could be differentiated into three regions, i.e., 1) yielding of the workpiece material, 2) intermediate deformation region, and 3) filling of the die. The results show that the optimum position of the AE sensor for monitoring hot forging is found to be the bottom die of the forging press. 相似文献
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An automatic calibration instrument was developed to improve the calibration accuracy of acoustic emission (AE) instrumentation. The instrument facilitates calibration by automatically displaying the maximum value of the stress used to produce AE calibration pulses and the AE pulse. A repeatable AE signal was generated by breaking a graphite rod on the test assembly. By measuring the breaking load of the rod and the maximum root-mean-square values of the resulting AE signals, a relative calibration of the AE measurement system was achieved. Low-noise amplifiers and filters were developed to improve the sensitivity of AE measurements by more than one order of magnitude over commercially available instruments; thus, the smaller signals obtained in parts testing can be detected 相似文献
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Discrimination of acoustic emission (AE) signals related to different damage modes is of great importance in carbon fiber-reinforced plastic (CFRP) composite materials. To gain a deeper understanding of the initiation, growth and evolution of the different types of damage, four types of specimens for different lay-ups and orientations and three types of specimens for interlaminar toughness tests are subjected to tensile test along with acoustic emission monitoring. AE signals have been collected and post-processed, the statistical results show that the peak frequency of AE signal can distinguish various damage modes effectively. After a AE signal were decomposed by Empirical Mode Decomposition (EMD) method, it may separate and extract all damage modes included in this AE signal apart from damage mode corresponding to the peak frequency. Hilbert-Huang Transform (HHT) of AE signals can clearly illustrate the frequency distribution of Intrinsic Mode Functions (IMF) components in time-scale in different damage stages, and can calculate accurate instantaneous frequency for damage modes recognition to help understanding the damage process. 相似文献
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The finite geometry of a laboratory specimen influences a measured acoustic emission waveform because of reflections, transmission,
and mode conversion at the interface and boundaries of the specimen, thus making it difficult to determine the location of
an acoustic emission (AE) source. The objective of this investigation is to develop a model experiment to identifiy the exact
source location on the surface using ``synthetic' AE signals. The AE event is generated by a short local thermal expansion.
This expansion is produced by the absorption of a short laser pulse which provides a noncontact and broad-band generation
of elastic waves. The signals are detected by a noncontact, broad-band, and high-fidelity sensor: a laser interferometer.
The triangulation with several detectors is replaced by a single probe laser interferometer located at different coordinates
under reproducible conditions. The recorded signals are analyzed by wavelet transform in order to determine the arrival times
of waves for several frequency levels. These arrival times are used to quantify the location of the AE source in the surface
as well as the velocity of the most dominant feature, the Rayleigh wave, and the time lag between the instant of the AE and
the recording of the signal. The accuracy of the method is demonstrated by comparing the identified source location with the
exact one. 相似文献
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H. Bi Z. Li D. Hu I. Toku‐Gyamerah Y. Cheng 《Materialwissenschaft und Werkstofftechnik》2015,46(7):736-746
The pitting corrosion characteristics of low carbon steel specimens are studied by acoustic emission (AE) and electrochemical techniques, in a 3.0 wt.% NaCl solution acidified to pH 2.0. The acoustic emission signals generated by pitting corrosion are classified based on multiple acoustic emission parameters using K‐means clustering algorithm, then each classified signals are analyzed by acoustic emission parameters correlation plot and distribution with time. Furthermore, each acoustic source characteristics is extracted using Gabor wavelet transform (WT) in the time and frequency domain. An error back propagation (BP) artificial neural network (ANN) is trained according to the classified signals, so as to successfully identify the acoustic emission signals from parallel experiments. Experimental results show that the hydrogen bubble activation, oxidized film rupture and pit growth are typical acoustic emission sources in pitting corrosion process, which can be effectively classified by cluster analysis and recognized by back propagation neural network. The data gathered from laboratory tests combined with the real data from acoustic emission on‐line storage tank floor inspection can help to evaluate the bottom corrosion severity and interpreter the corrosion source, further to make the on‐site testing more reliable and reduce the risk. 相似文献
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Smith GC 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2005,52(9):1613-1617
A noncontact method for detecting acoustic emission was developed, using a microwave Doppler radar detector and an active band-pass filter. A theoretical model was developed and a prototype sensor was built and tested. The prototype responds to acoustic emissions (AE), from pencil lead break tests, at ranges up to 1.5 feet. 相似文献