混凝土桥梁裂缝的无损检测技术及修补

本文介绍了混凝土裂缝检测与监测的方法,针对混凝土桥梁常见裂缝裂缝的修补进行了探讨。     

基于图像分析的路面裂缝检测和分类

将二维路面图像映射到三维曲面,裂缝经映射后对应于三维曲面中的"山谷",采用基于微分几何的空间检测算子提取三维曲面中的"山谷",反映射到二维图像平面作为裂缝目标.对裂缝目标进行路径增长以获取裂缝长度信息,并以此作为判断真伪裂缝的依据,由此可消除绝大部分伪裂缝.根据不同类型裂缝的几何形态,抽取裂缝模式特征,设计基于BP神经网络的模式分类器实现对裂缝的精确分类.     

钢筋混凝土框架梁裂缝原因和处理措施

本文结合具体工程对钢筋混凝土框架梁裂缝的原因进行了分析，提出了具体的处理措施，供大家参考。     

浅谈混凝土结构裂缝的检测

本文阐述了混凝土结构裂缝的分类与检测技术,对类似工程有一定的参考价值。     

住宅施工中常见质量问题监控探讨

本文对住宅建筑工程施工中常见的问题和检测方法进行了分析，并提出相应的控制对策，供大家参考。     

钢筋混凝土框架梁裂缝原因和处理措施

本文结合具体工程对钢筋混凝土框架梁裂缝的原因进行了分析，提出了具体的处理措施，供大家参考。     

地下室剪力墙裂缝的检测及处理实例研究

本文以某地下室剪力墙裂缝为例,结合《房屋裂缝检测与处理技术规程》(CECS293:2011),介绍了地下室剪力墙裂缝的检测及处理。     

碾压混凝土坝裂缝处理效果的检测与分析

论述了碾压混凝土坝裂缝检测方法，以及裂缝处理后的检测处理效果，裂缝前期检测采用超声波仪进行检测，效果检测采用超声波仪和钻孔对测比较法进行检测对比，分析了裂缝处理前后的状态，给工程验收及相类似工程有一个很好借鉴作用。     

混凝土表面开口裂缝对近表面声波影响

基于混凝土近表面不同波型的声速,分析开口裂缝对声波的影响。有限元仿真结果表明,激励源辐射的初始纵波P经裂缝端点衍射产生纵波P-P与横波P-T,P-T以一定的角度射向混凝土表面经模式转换产生纵波P-T-P;初始横波T在裂缝端点衍射产生纵波T-P与横波T-P;初始瑞利波R在裂缝端点衍射后除了产生纵波R-P与横波R-S外继续沿着固体表面传播(R-R)。在此基础上,基于变型波到达接收阵元的时刻定量检测裂缝的深度,检测结果较单面平测法具有更高的信噪比与检测精度,可辅助单面平测法更精确地定量检测混凝土开口裂缝的深度。     

混凝土桥梁裂缝无损检测技术和修补探讨

本文分析了无损检测技术的意义和桥粱常见裂缝的危害,并总结混凝土裂缝检测与监测的方法,最后介绍裂缝的修补及加强技术,供大家参考。     

Acoustoelastic Effects in Elastic Media with Nonuniform Initial Stress

Abstract

A perturbative formalism for the treatment of the acoustoelastic effect in material plates with a stress profile in the thickness direction is proposed and compared with a numerical method. The latter consists of an application of the local interaction simulation approach (LISA). The reliability of both the analytical treatment and the numerical approach is tested by comparing the respective results for several cases of propagation of Rayleigh waves in specimens with various kinds of stress fields, including welded steel plates. Finally, the linearization obtained from the perturbation treatment is exploited for the solution of the “inverse problem,” i.e., the determination of the stress field from a set of RW times of flight with different wavelengths. A numerical example is provided to illustrate the applicability of the method, starting from a set of synthetic data obtained with LISA.     

Validity of bolt-removal and gap-insertion techniques to experimentally simulate the vibration of a cracked rotor

Experimental studies of the vibration of a cracked rotor are essential in the development of vibration monitoring techniques. The greatest difficulty in conducting experimental parameter studies is the extensive amount of work required when placing a fatigue crack (FC) of known size and location in the structure. Two alternative techniques, the bolt‐removal method (BRM) and the gap‐insertion method (GIM), have been suggested to provide an easy mechanism to experimentally simulate the behaviour of a breathing crack. This study aims to qualitatively and quantitatively evaluate these methods and compare them with the results from a grown FC in a slow rotating drum specimen. Deflection results show good agreement, particularly in the vertical direction. For the horizontal direction the two simulation techniques overestimate the deflection from the FC for large crack sizes. However, overall GIM and BRM provide close enough results to support the usage in experimental parameter studies at significantly lower cost.     

基于弱磁技术的火车轮踏面裂纹检测

针对火车轮踏面易萌生细小裂纹的问题,提出一种无需励磁,利用地磁场磁化的无损检测方法.根据火车轮踏面结构设计探头工装,利用弱磁检测仪器采集车轮踏面磁感应强度信号,分析预制裂纹缺陷的磁异常信号特征,对比不同深度裂纹的磁异常信号幅值,通过傅里叶最小二乘拟合得到缺陷深度的定量算法,根据极值差法与拉依达准则对火车轮踏面进行智能识...     

Crack path tracking from full field measurements: A novel empirical methodology

The identification of crack growth models requires the knowledge of the crack path geometry and, in particular, of the crack tip position. The objective of the present paper is to provide a criterion for the detection of the crack tip position regardless of the loading conditions or the material behavior. The novelty of the proposed approach is its ability to provide a good estimation of the crack tip even when large plastic deformations occur. The proposed empirical criterion uses the evolution of the displacement gradient standard deviation along a potential crack path to locate the crack tip. It thus relies on full field measures that are relatively smooth while providing accurate displacement vectors even close to the lips. We successfully apply the proposed criterion in two cases of fatigue crack growth: A straight crack at high temperature and a curved crack at room temperature involving large plastic deformations.     

The effect of damping and force application point on the non-linear dynamic behavior of a cracked beam at sub-and superresonance vibrations

The finite element model of an elastic body with a closing crack is presented. Using this model, we show that the non-linear distortions of vibrations at superharmonic and subharmonic resonances are the high sensitive indicators of crack presence. The intensity of these indicators manifestation substantially depends on the level of damping in the system and on the load application point. __________ Translated from Problemy Prochnosti, No. 5, pp. 61–67, September–October, 2006. Report on International Conference “Dynamics, Strength, and Life of Machines and Structures” (1–4 November 2006, Kiev, Ukraine).     

基于模态参数的海洋平台损伤检测

将基于不同模态特性参錾的损伤检测方法应用于海洋平台，研究适用于海洋平台裂纹损伤的模态参数检测方法。通过对海洋平台进行结构模态分析，针对在平台不同位置有损伤和在同一位置有不同程度损伤的情况，利用有限元法计算了平台结构的前十阶固有频率与振型，研究不同的结掏模态特性参数对损伤、损伤位置和损伤程度的敏感性，并分析了利用顶部构件的局部振型对平台底部的裂纹损伤进行损伤俭测的可行性，为平台的现场检测提供有价值的参考。     

Structural damage identification using transfer matrix with lumped crack properties

A novel damage detection scheme is developed for detecting multiple cracks in beams, based on a transfer matrix (TM) approach. Lumped Crack TM of a beam element with multiple cracks is derived based on lumped crack properties. A cracked beam element is assumed as two intact beam elements connected with a hinge or torsional spring. The crack is modelled as an element of zero length and mass, but with elastic properties. Lumped crack approach is simpler for multiple cracks than the possible alternative methods. The state vector at a node includes displacements, forces and moments at that node; when it is multiplied with TM the state vector at the adjacent node can be obtained. The crack identification strategy used here, involves measuring the initial state vector at a node, in the zone of interest. The displacements at the adjacent nodes are measured and these are predicted using TM. Using an optimization algorithm the unknown crack parameters in the TM are solved by minimizing the deviation between measured and predicted displacements. The method is verified using several numerical models as well as experiments with cracked beams. The TM is shown to be suitable for local identification and also fast and accurate compare to other methods.     

含损伤梁的三维有限元压电阻抗模型及参数研究

采用有限元软件ANSYS进行数值模拟分析,构建了含损伤梁的三维有限元压电阻抗（EMI）模型。分析中考虑粘结层的影响,将压电片-粘结层-主体结构作为整体耦合系统加以考察。与实验数据以及其它研究结果进行了对比分析,验证了该有限元压电阻抗模型的有效性和精确性。考察了各物理参数对压电阻抗信号的影响,尤其是梁中裂纹的出现和发展对电阻抗谱的作用。计算结果表明该压电阻抗模型能用于结构损伤识别。最后,讨论了有限元单元尺寸的选取对高频振动分析结果的影响。     

Comparison between piezoelectric method and ultrasonic signal analysis for crack detection in type II multilayer ceramic capacitors

In this paper we present a comparison between two non-destructive techniques for crack detection in MLCCs. First, if a type II MLCC is biased with a DC field, the capacitor becomes temporarily ‘poled’ and can act as a transducer. This is induced by a residual piezoelectric effect used in the impedance spectroscopy method. Second, we used a scanning ultrasonic system working in the 10–100 MHz frequency bandwidth. To understand the ultrasonic signature, we used time-of-flight (TOF) detection with short-time Fourier transform (STFT) analysis to determine the depth and nature of defects with high accuracy. An application of digital signal processing to the characterization of defects is presented for a lot of MLCCs with cracks defects. For comparison, the same lot was tested with the piezoelectric method. The two techniques are closely correlated. © 1998 John Wiley & Sons, Ltd.     

自然环境下路面裂缝的识别

论文提出了一种基于分数阶微分和图像形态学的路面裂缝检测算法。分数阶微分能有效增强信号中、高频部分,非线性保留信号的低频部分,通过构建分数阶微分掩模算子,增强裂缝信息特别是平滑区域中弱信号信息。利用图像形态学算子提取裂缝,通过组合中值滤波去除孤立噪声点。实验结果表明,该算法比传统算法能更有效地检测出细小裂缝信息,是一种具有较强鲁棒性且高效实用算法。