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详细阐述了冲击回波检测方法的原理及其在土木工程中的应用,结合厦门市某大桥,采用冲击回波法对箱梁预应力束孔管道的压浆质量进行无损检测.首先在完全灌浆的预应力钢束管道位置和正常混凝土位置(即无波纹管位置)进行测试,获得混凝土内部压浆密实和无预应力管道时的两组冲击回波频谱图,作为与测点检测结果进行对比的基础,根据时频谱图的分析结果可以预测钢束管道内的压浆质量,判断孔道中是否有空隙存在.经检测与分析表明,冲击回波法是可行的,适用于预应力束孔管道的压浆质量检测. 相似文献
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采用冲击回波法检测混凝土厚度或者缺陷时,采用传统快速傅里叶变换方法,由于傅里叶变换的时移性以及信号中包含表面波和结构模态振动使得特征频率的提取较为困难。要解决特征频率提取受到干扰的问题,该文提出一种小波变换结合傅里叶变换的信号处理方法。首先对回波信号进行小波变换,得到信号时频图和小波边际谱,其次将小波边际谱与傅里叶谱相乘,得到增强傅里叶谱。结果表明:信号时频图可以确定表面波和模态振动的频率范围和时间跨度,增强傅里叶谱不仅可保证频率分辨率,而且抑制由于傅里叶变换的时移性产生的多个波峰,使得特征频率在频谱中更为清晰和准确,是一种适用于冲击回波检测的信号处理方法。 相似文献
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超声反射法测量混凝土厚度 总被引:1,自引:0,他引:1
一 、前言 在超声检测领域中,反射法占有重要地位,而准确地提取材料中各界面的反射回波声时(或谐频),则是反射法超声检测的一个基本课题。 对于低衰减、非频散的均匀介质材料,反射法超声检测已很成熟,而对于高衰减、频散严重的多相材料体系,如混凝土等,由于有用回波信号衰减过快:频散及模式转换,使得有用信号微弱且伴有畸变,很难予以分辨。 本文试图采用几种超声反射方法来测量混凝土试样的厚度,比较了几种超声探头、冲击回波等接收信号的直读和波形信号处理方法。实验表明:1.普通窄带超声探头的直达与反射信号余振均很长,不能直接读出其厚… 相似文献
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电解槽的寿命及修复关系着整个电解铝行业的经济效益,是不容忽视的技术问题。为能对破损电解槽进行及时修复从而延长电解槽寿命,提出应用冲击回波法对电解槽破损状况进行评估。首先利用数值模拟方法探讨了冲击回波激振源特性对应力波脉冲宽度及应力峰值的影响,得出激振源直径D与脉冲宽度tc呈线性相关:tc=0.004D,且与应力峰值(P)呈指数相关P=2e~8D1.928 8,而冲击速度v不改变脉冲宽度tc,但与应力峰值P呈线性相关:P=0.0751v-0.068 6。进而基于数值分析结果,运用冲击回波法检测破损电解槽中的阴极钢棒,通过对检测结果的时频域分析,得出了阴极钢棒的破损状况及位置,并与刨槽后真实的阴极钢棒对比。结果表明:冲击回波法能很好地实现电解槽破损部位的定位,可为电解槽寿命评估与修复提供参考。 相似文献
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Non-linear ultrasonic testing, based on higher order harmonic generation, is a true mean for nondestructive evaluation of concrete allowing damage detection at early stages of damage. Using conventional non-destructive testing methods like pulse echo, velocity and impact echo for evaluation of such damages is difficult because poor sensitivity of these methods to early damage occurrence. In this paper an experimental investigation of 18 cubic concrete specimens, caste with three different water–cement ratios, using non-linear ultrasonic technique is presented. The specimens were ultrasonically evaluated both in damaged and undamaged conditions. The specimens were damaged progressively by loading them under compression in several steps up to their ultimate load bearing capacity. At the end of each loading step ultrasonic evaluation was performed and time domain waveforms were recorded at different power levels. Frequency spectra were prepared by performing Fast Fourier Transformation of the recorded time domain waveforms. The frequency spectra were used to obtain the first three harmonic amplitudes. The captured harmonic amplitudes were used to calculate the second and third harmonic ratios. Comparison of the harmonic ratios has shown the extraordinary sensitivity of the non-linear ultrasonic method, used in this study, to early damage detection. It was also observed that this sensitivity further increases as water cement ratio increases. 相似文献
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The commercially available impact echo assessment is effective in assessing flaws in concrete but the evaluation is manual, thus, to evaluate large area by this method is neither practical nor cost effective. In order to enhance the method in application to reinforced concrete slab such as bridge decks, where duration of investigation plays substantial influence on traffic activity, data analysis and interpretation should not only be rapid and objective but also should provide automatic documentation of assessment results straight away at the end of the investigation. This research paper describes a new approach for impact echo method with automatic interpretation of signal through an algorithm. The algorithm detects the defect; calculates its depth and the assessment result is presented in 2D view instantaneously. The algorithm is verified by means of an experimental study, which is conducted with four reinforced concrete slabs incorporating induced delamination, void and honeycombing. A software named Imco@slab is developed based on this algorithm. Finally, a field study over reinforced concrete slab using this software has been conducted and its applicability in practical sense is verified. The field study shows that the discrepancy in assessment by Imco@slab interpretation with hammer tapping method and conventional manual impact echo method is negligible. This software is applicable in assessing delamination and void defects in reinforced concrete slabs. 相似文献
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Non-destructive testing (NDT) of concrete structures plays an increasing role in civil engineering. At present there are several acoustic and electromagnetic methods, which cover a large area of application and which can be used complementarily. But in most cases, only one method is applied to solve a distinct problem. In this contribution, results will be presented based on the networked research project FOR384, funded by the Deutsche Forschungsgemeinschaft (DFG). Among others, the combiantion of NDT methods, and thus the application of data fusion techniques, has been investigated to demonstrate synergetic effects by merging complementary results and amplifying information about concrete structures. In order to be able to combine NDT-data from several methods recorded from the same volume, the different data sets must, be adapted. After the data sets are reconstructed and transferred into a common reference system, they can be processed in different ways according to the purpose of the investigation. The results, which have been achieved in concrete tets specimens and on the carriageway of a bridge with radar, ultrasonic echo and impact echo, will be presented and will show the feasibility of the data fusion method. 相似文献
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Ilker Boz Korkut Bekiroglu Mansour Solaimanian Pezhouhan Tavassoti-Kheiry Constantino Lagoa 《Journal of Nondestructive Evaluation》2017,36(3):58
The impact resonance test is a free vibration-based nondestructive test method that has been increasingly used in evaluation and characterization of asphalt concrete for the past two decades. The rheological modeling of the impact resonance test is conceptualized by a linear viscous damping mechanism having single degree of freedom whose equation of the motion is assumed to be second order. In this study, the second order equation of motion assumption in the modeling of the impact resonance test response was evaluated for asphalt concrete testing. A set of asphalt concrete specimens was tested with the impact resonance test, and the obtained signals at a range of temperatures were evaluated by means of the Hankel matrix method. The results showed that the assumption is violated for asphalt concrete testing especially at high temperatures, mainly due to the presence of noise in the obtained response. However, the Hankel method was employed to filter out the noise. It was seen that the assumption could be employed for asphalt concrete at a range of temperatures including high temperatures, provided that the filtering is performed on the obtained signal. The results also showed that the employed filtering procedure produced improvements for the impact resonance test material dependent responses, resonant frequency and especially damping ratio calculations. 相似文献
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Depending on the nature of the working environment, the abrasive wear of concrete floor slabs can range from scratching or
scuffing to impact and local crushing. To assess abrasion resistance it is, therefore, necessary to have a versatile apparatus.
This investigation describes the development of a basic apparatus with three modes of action and a standardized testing procedure,
for assessing the abrasion resistance of concrete slabs in the industrial environment. It consisted of a rotating plate carrying
a total load of 65 kg so that it was sufficiently portable for both laboratory and site testing. Three different types of
abrasion head—(a) revolving pads, (b) rolling wheels, (c) dressing wheels—could be fixed to the plate so that the effects
of different modes of wear could be assessed. The abrasion resistance is expressed in terms of the depth of the groove produced
by 15 min of abrasion. A laboratory programme was undertaken to assess the apparatus and test method. The factors examined
included the methods of assessing the abrasive wear, the duration of the test, the minimum number of tests to reliably assess
the abrasion resistance, the relative performance of the three types of test head and the mechanism(s) by which each head
abraded the concrete surface. Consequently a standardized procedure was developed which was found to be sensitive to variations
in surface conditions. This has the additional advantages of simulating service conditions and of being repeatable, easy to
follow and with the cost and time of testing not being excessive. 相似文献
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Field studies have suggested that wave velocities through concrete samples decrease with increasing damage. However, to date there has been no replication of this effect in a laboratory setting allowing for a controlled experiment to quantify this effect. The primary objective was to see how the exposure of concrete to sulfate solutions related to surface-wave velocity and through-wave velocity. The impact–echo method and the ultrasonic pulse velocity test were used to quantify these relationships, respectively. Laboratory research focused on correlating nondestructive test (NDT) data with destructive test results from field-sized concrete samples exposed to continuous sulfate attack over time. The intent was to evaluate the capabilities of the NDT techniques in identifying and quantifying damage due to sulfate attack. Prior research has shown that tension testing tends to be far more sensitive than compression testing to such damage. As a result, it was expected, and confirmed, that stress wave velocities from the two NDT techniques correlate better with tensile strength than with compressive strength. 相似文献
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Ernian Pan 《International Journal of Fracture》1997,88(1):41-59
This paper presents a boundary element method (BEM) analysis of linear elastic fracture mechanics in two-dimensional solids.
The most outstanding feature of this new analysis is that it is a single-domain method, and yet it is very accurate, efficient
and versatile: Material properties in the medium can be anisotropic as well as isotropic. Problem domain can be finite, infinite
or semi-infinite. Cracks can be of multiple, branched, internal or edged type with a straight or curved shape. Loading can
be of in-plane or anti-plane, and can be applied along the no-crack boundary or crack surface. Furthermore, the body-force
case can also be analyzed. The present BEM analysis is an extension of the work by Pan and Amadei (1996a) and is such that
the displacement and traction integral equations are collocated, respectively, on the no-crack boundary and on one side of
the crack surface. Since in this formulation the displacement and/or traction are used as unknowns on the no-crack boundary
and the relative crack displacement (i.e. displacement discontinuity) as unknown on the crack surface, it possesses the advantages
of both the traditional displacement BEM and the displacement discontinuity method (DDM) and yet gets rid of the disadvantages
associated with these methods when modeling fracture mechanics problems. Numerical examples of calculation of stress intensity
factors (SIFs) for various benchmark problems were conducted and excellent agreement with previously published results was
obtained.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Bai J Ding C Luo J He P 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(5):541-549
In cross-correlation based elastography, the quality of the strain image is degraded by the distortion of echo waveforms due to tissue axial and lateral displacement. To study the effects of tissue lateral displacement on echo decorrelation, a tissue axial stretching model is developed and a concept called correlation signal-to-noise ratio (CSNR) is introduced to quantify the decorrelation effect due to tissue lateral displacement. A computer simulation based on the tissue stretching model is carried out to study the influence of several important elastographic parameters on echo decorrelation due to tissue lateral displacement. Finally, guided by the CSNR concept, a 2-D spatial comprehensive cross-correlation method is proposed to reduce the decorrelation noise. Results indicate that CSNR can be used as a quality indicator of elastography and the 2-D spatial comprehensive cross-correlation method can effectively reduce the decorrelation noise while slightly decreasing the lateral resolution of the strain image 相似文献
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This paper performs drop-weight splitting tests to study the dynamic tensile properties of fibre reinforced concrete (FRC) materials with different steel fibres. A renovated splitting tensile testing method was developed to ensure a more qualified experimental process. The splitting tensile impact tests were conducted with an instrumented drop-weight impact system consisting of a hard steel drop weight, a fast-response load cell, a high-speed video camera and a high-frequency data acquisition system. The quasi-static compressive and splitting tests were also conducted to obtain the static properties of the FRC materials. The commonly used hooked-end steel fibre and a new spiral shaped steel fibre were tested in this study. The high-speed video camera was used to capture the detailed failure process, deformation and cracking process of the tested specimens. Average strain rates and the cracking extension displacement and velocity under impact loading were estimated by analysing the recorded high-speed images. The strains were also measured by the strain gages on the specimen surface. The dynamic stress–strain and stress–COD (cracking opening displacement) relations, the rate sensitivity of tensile strength and the corresponding energy absorption capacity of plain concrete and FRC with different fibres were obtained, compared and discussed. The advantage and effectiveness of the new spiral fibre in increasing the performance of FRC under dynamic tensile loading were examined. The results show that FRC with spiral fibres outperforms that with hooked-end fibres, and is a promising construction material in resisting dynamic loadings. 相似文献