结构健康监测中的损伤检测技术研究进展

对结构健康监测研究中的结构损伤检测方法及其特点进行了介绍.从基于结构模态分析的方法和基于结构动态试验信号处理的方法两方面,阐述了结构健康监测中的损伤检测方法及其最新研究进展.基于结构模态分析的结构损伤检测方法是针对整个结构的检测,使用的模态都限于低阶模态范围内,所检测的结构应容易建立有限元模型,便于进行响应预测.基于结构动态试验信号处理的损伤检测方法通常是针对结构局部构件的损伤检测,不需要对结构进行有限元建模,而直接从测试的动态响应信号中提取表征结构损伤的特征参数.文中提出了对比性损伤检测方法和非对比性损伤检测方法的概念,并对结构损伤检测中常用的信息传感与处理技术进行了论述,指出了结构损伤检测研究中应该考虑的传感器布置问题.提出了将损伤信息的主动检测与被动检测相结合进行损伤程度判断和剩余寿命估计等问题是有待进一步深入研究的课题.      

Structural health monitoring and damage detection using an intelligent parameter varying (IPV) technique

Most structural health monitoring and damage detection strategies utilize dynamic response information to identify the existence, location, and magnitude of damage. Traditional model-based techniques seek to identify parametric changes in a linear dynamic model, while non-model-based techniques focus on changes in the temporal and frequency characteristics of the system response. Because restoring forces in base-excited structures can exhibit highly non-linear characteristics, non-linear model-based approaches may be better suited for reliable health monitoring and damage detection. This paper presents the application of a novel intelligent parameter varying (IPV) modeling and system identification technique, developed by the authors, to detect damage in base-excited structures. This IPV technique overcomes specific limitations of traditional model-based and non-model-based approaches, as demonstrated through comparative simulations with wavelet analysis methods. These simulations confirm the effectiveness of the IPV technique, and show that performance is not compromised by the introduction of realistic structural non-linearities and ground excitation characteristics.     

Application of particle swarm optimization and genetic algorithms to multiobjective damage identification inverse problems with modelling errors

Structural health monitoring has become an important research topic in conjunction with the damage assessment of structures. The use of system identification approaches for damage detection using inverse methods has become more widespread in recent years and their formulation in a multiobjective framework has become more usual. Inverse problems require the use of an initial baseline model of the undamaged structure. Modelling errors in the baseline model whose effects exceed the modal sensitivity to damage are critical and make an accurate estimation of damage impossible. Artificial intelligence techniques based on genetic algorithms are used increasingly as an alternative to more classical techniques to solve this kind of problem especially due to their feasibility for managing multiobjective problems. This paper outlines an understanding of how particle swarm optimization methods operate in damage identification problems based on multiobjective FE updating procedures and takes modelling errors into account. One experimental example is used to show their performance in comparison with genetic algorithms.     

Wavelet packet based damage identification of beam structures

Most of vibration-based damage detection methods require the modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such a good sensitive indication of structural damage. The wavelet packet transform (WPT) is a mathematical tool that has a special advantage over the traditional Fourier transform in analyzing non-stationary signals. It adopts redundant basis functions and hence can provide an arbitrary time-frequency resolution. In this study, a damage detection index called wavelet packet energy rate index (WPERI), is proposed for the damage detection of beam structures. The measured dynamic signals are decomposed into the wavelet packet components and the wavelet energy rate index is computed to indicate the structural damage. The proposed damage identification method is firstly illustrated with a simulated simply supported beam and the identified damage is satisfactory with assumed damage. Afterward, the method is applied to the tested steel beams with three damage scenarios in the laboratory. Despite the noise is present for real measurement data, the identified damage pattern is comparable with the tests. Both simulated and experimental studies demonstrated that the WPT-based energy rate index is a good candidate index that is sensitive to structural local damage.     

Bifurcation boundary analysis as a nonlinear damage detection feature: does it work?

Many systems in engineering and science are inherently nonlinear and require damage detection. For such systems, nonlinear damage detection methods may be useful. A bifurcation boundary analysis method as a new nonlinear damage detection tool was previously introduced in the literature to track bifurcation boundary changes due to damages over a small region of an aeroelastic panel model. Results of this method based upon a finite difference solution showed higher sensitivities to the small amount of damage than methods based upon linear models. In this paper, four methods including Finite Difference, Finite Element (FEM), Rayleigh-Ritz and Galerkin Approach are used to further investigate the sensitivity of the bifurcation boundary for damage detection. Results of the FEM and Rayleigh-Ritz method agree with each other and also show that the sensitivity of the bifurcation boundary to damage is much less than what previously reported when using a finite difference solution method.     

Damage localization using transient non-linear elastic wave spectroscopy on composite structures

To reduce the costs related to maintenance of aircraft structures, there is the need to develop new robust, accurate and reliable damage detection methods. A possible answer to this problem is offered by newly developed non-linear acoustic/ultrasonic techniques, which monitor the non-linear elastic wave propagation behaviour introduced by damage, to detect its presence and location.In this paper, a new transient non-linear elastic wave spectroscopy (TNEWS) is presented for the detection and localization of a scattered zone (damage) in a composite plate. The TNEWS analyses the uncorrelations between two structural dynamic responses generated by two different pulse excitation amplitudes by using a time-frequency coherence function. A numerical validation of the proposed method is presented. Damage was introduced and modelled using a multi-scale material constitutive model (Preisach-Mayergoyz space).The developed technique identified in a clear manner the faulted zone, showing its robustness to locate and characterize non-linear sources in composite materials     

A new nonlinear elastic time reversal acoustic method for the identification and localisation of stress corrosion cracking in welded plate-like structures – A simulation study

In order to reduce the costs related to corrosion damage in aircraft structures, it is vital to develop new robust, accurate and reliable damage detection methods. A possible answer to this problem is offered by newly developed nonlinear ultrasonic techniques, which monitors the nonlinear elastic wave propagation behaviour introduced by damage, to detect its presence and location.In this paper, a new nonlinear time reversal technique is presented for the detection and localization of a scattered zone (damage) in a multi-material medium. In particular, numerical findings on a friction stir-welded aluminium plate-like structure are reported. Damage was introduced in the heat affected zone and modelled using a multi-scale material constitutive model (Preisach–Mayergoyz space).Studies were conducted for two different transducer configurations. Particular attention was devoted to find the optimum time-reversed window to be re-emitted in the structures. The methodology was compared with traditional time-reversal acoustics (TRA), showing significant improvements. While the traditional TRA was not able to clearly localise the damage, the developed technique identified in a clear manner the faulted zone, showing its robustness to locate and characterize nonlinear sources, in presence of a multi-material medium.     

Nondestructive testing method based on lamb waves for localization and extent of damage

Based on Lamb wave analysis of propagation in plate-like structures, a damage detection method is proposed that not only locates the position of the damage accurately but also estimates its size. Similar damage detection methods focus only on localization giving no quantitative estimation of extent. To improve detection, we propose two predictive circle methods for size estimation. Numerical simulations and experiments were performed for an aluminum plate with a hole. Two PZT configurations of different sizes were designed to excite and detect Lamb waves. From cross-correlation analysis, the damage location and extent can be determined. Results show that the proposed method enables a better quantitative resolution in detection, the size of the inspection area influences the accuracy of damage identification, and the closer is the inspected area to the damage, the more accurate are the results. The method proposed can be developed into a multiple-step detection method for multi-scale analysis with prospective accuracy.     

Noise analysis for sensitivity-based structural damage detection

As vibration-based structural damage detection methods are easily affected by environmental noise, a new statistic-based noise analysis method is proposed together with the Monte Carlo technique to investigate the influence of experimental noise of modal data on sensitivity-based damage detection methods. Different from the commonly used random perturbation technique, the proposed technique is deduced directly by Moore-Penrose generalized inverse of the sensitivity matrix, which does not only make the analysis process more efficient but also can analyze the influence of noise on both frequencies and mode shapes for three commonly used sensitivity-based damage detection methods in a similar way. A one-story portal frame is adopted to evaluate the efficiency of the proposed noise analysis technique.     

基于时间反转法的Lamb波检测技术的研究进展

Lamb波具有传播距离远、衰减小等特点,已被广泛应用于大型板类结构的损伤检测。时间反转是实现超声波聚焦的有效方法之一。本文回顾并总结了近20年来时间反转方法在Lamb波检测领域中的研究进展。针对Lamb波固有的频散和多模态等传播特性,详细论述了时间反转法在板结构Lamb波检测中的应用。最后对基于时间反转法的免基准信号Lamb波损伤检测方法进行了总结,分析其存在的问题并对其应用前景进行了展望。     

A Fully Non-Contact Ultrasonic Propagation Imaging System for Closed Surface Crack Evaluation

Cracks are one of the most common types of damage occurring in engineering structures. A reliable nondestructive evaluation technique is essential to detect any possible damage at the initiation phase. Real fatigue closed-surface cracks are difficult to detect through visual inspection. Ultrasound has been widely used, but conventional contact ultrasonic inspection techniques are not suitable for couplant-sensitive structures. In addition, these techniques are generally laborious for large field structures and the inspection speed is relatively slow. We present a novel fully non-contact hybrid ultrasonic propagation imaging (UPI) system that uses laser ultrasonic scanning excitation and piezoelectric air-coupled sensing. Ultrasonic frequency tomography and wavelet-transformed ultrasonic propagation imaging algorithms are used to extract damage features. These features are used to perform a thorough diagnosis of damage. The system enables remote and fully non-contact automatic one-sided inspection for temporal reference-free damage evaluation, and is also applicable to in-field structures. Optimization provides improved performance of air-coupled transducers (ACTs) used as receivers for the hybrid UPI system, as shown by our experimental results. Surface crack evaluation results were analyzed on the basis of ease of damage visualization, accuracy of crack size estimation, and sensitivity. The proposed hybrid UPI system is sensitive enough to detect a real fatigue closed-surface micro-crack with size detection accuracy as high as 96%. We also show that the relation between the scanning interval and crack width affects damage visualization performance, and the accuracy and sensitivity of damage size estimation.     

On the use of non-linear vibrations and the anti-resonances of Higher-Order Frequency Response Functions for crack detection in pipeline beam

The identification of new scientific challenges, as well as the increasing high-performance computing support, indicates that the benefits of applying novel nonlinear techniques for crack detection will continue to grow. So, significant effort has been invested in recent years to develop effective techniques to detect crack in mechanical structures. The objective of this paper is to discuss and propose a robust diagnostic of damage based on non-linear vibrational measurements with particular regard to the Higher-Order Frequency Response Functions. An important observation is that the appearances of the non-linear harmonic components and the emerging anti-resonances in Higher-Order Frequency Response Functions can provide useful information on the presence of cracks and may be used on an on-line crack monitoring system for small levels of damage. Efficiency of the proposed methodology is illustrated through numerical examples for a pipeline beam including a breathing crack.     

复合材料板冲击损伤检测的二维间隔平滑法

本文发展了一种基于振动的复合材料板的损伤检测方法,将原有的一维间隔平滑法(1D GSM,one dimensional gapped smoothing method)发展至二维(2D GSM),并进一步提出二维间隔平滑法的标准化损伤指标.与其他多数基于振动分析的损伤检测方法不同,该方法只需分析含有损伤结构的检测数据,无需结构健康时的数据或理论、计算结果作为对比信号,即可判定缺陷的存在,并能准确定位.针对由冲击造成的准各向同性碳纤维增强复合材料板中的层裂损伤,本文采用压电片阵列组合激励的方式,得到了复合材料板多频率扭转振型的同时激励,可实现快速、高效的损伤检测.通过扫描式激光测振仪测得结构在不同固定频率下的结构响应ODS(operational deflection shapes),利用提出的二维间隔平滑法,分析得出损伤指标.实验结果表明,二维间隔平滑法可以准确地检测碳纤维增强复合材料板的冲击损伤,并具有较好的精度.     

结构损伤探测的基本方法和研究进展

对目前关于结构的损伤探测的基本方法和最新的研究进展进行了回顾主要介绍利用结构的振动响应和系统动态特性参数进行结构损伤探测的方法和研究进展,并进行了相应的评述．对利用应力波效应和神经网络技术的损伤探测方法也做了简要的介绍和评述．最后对这一研究领域未来的若干研究方向进行了展望．      

Understanding the effect of boundary conditions on damage identification process when using non-linear elastic wave spectroscopy methods

This paper presents an experimental campaign aimed at understanding the limitations and capabilities of non-linear elastic wave spectroscopy (NEWS) non-destructive technique (NDT) methods in the presence of variable boundary conditions. In particular, the objective was to understand if the contact between the structures under investigation and the clamps used to hold the structures could generate non-classical non-linear effects that could affect the damage detection process by producing false-positive indications of defects presence.Two different techniques were analysed with varying degree clamping torque. The first approach evaluates the resonance frequency shift as a function of the external load amplitude, and it is called non-linear resonant ultrasound spectroscopy (NRUS). The second method used, called non-linear wave modulation spectroscopy (NWMS), monitors the generation of sidebands and harmonics when the structure is excited by a double tone external load.The results showed that the non-classical hysteretical non-linear effects were dependent on the boundary conditions, highlighted by the presence of resonance shift and harmonics and sidebands in an undamaged sample. This research shows that more work is needed to demonstrate the effectiveness of the methods and the ease of implementation in a structural health monitoring system and further research studies and methodology development are needed to discern non-classical non-linear effects generated by contacts between mating parts (clamps and sample) from that generated due to the presence of damage.     

A Combined Static/Dynamic Technique for Damage Detection of Laminated Composite Plates

There is a growing demand to develop viable techniques for effective damage detection of composite structures, and the dynamics-based approach has been broadly used in structural health monitoring. A new combined static/dynamic technique for improved damage detection of laminated composite plates is presented. The promise of the technique is that under the sustaining static load, the abnormality of dynamic response due to damage may become more pronounced and easy to be detected. The experimental program consists of testing an E-glass/epoxy composite plate with an embedded delamination under a pre-set static compressive force, and the dynamic response of laminated composite plates is measured using two different actuator–sensor systems: (1) PZT (lead–zirconate–titanate) actuators and scanning laser vibrometer (SLV) sensing system (PZT–SLV), and (2) PZT actuators and Polyvinylidenefluoride (PVDF) sensors (PZT–PVDF). The influence of sustaining static forces to dynamic response of delaminated composite plates is evaluated. The numerical finite element (FE) analysis is also conducted to verify the effectiveness of this technique. The experimental and numerical mode shapes are used to detect the presence, location, and size of the delamination and to study the effect of static load on dynamic response. Two relatively new damage detection algorithms (i.e., Simplified Gapped Smoothing Method (GSM) and Generalized Fractal Dimension (GFD)) are employed to analyze the Uniform Load Surface (ULS) calculated from the experimental and numerical data. From the dynamic response and analysis results using the damage detection algorithms, it is observed that as the sustaining static load increases, the delamination is much easier to be identified through the enlarged damage parameters. The present combined static/dynamic technique is capable of magnifying the effect of damage, thus improving the effectiveness of damage detection.     

空间网格结构损伤探测的研究进展

空间网格结构损伤探测技术是目前结构工程领域研究的热点和难点．根据国内外的最新文献信息，讨论了损伤探测技术在空间网格结构中的应用及最新的研究进展，对现有文献中的方法进行了分类和评述．重点介绍了目前比较适用的柔度法和模型修正方法，对该领域中尚存在的问题进行了讨论，对今后的发展方向及趋势进行了展望．     

Experimental dynamic analysis of cracked free-free beams

The use of modal-analysis techniques as nondestructive methods for the detection of cracks in beams is a current field of interest for various researchers. However, an extensive search of the published literature shows that there is very little information on experimental results, thus making it almost impossible for theoretical researchers to use published experimental data to validate their models.The authors, who are currently working in the field of crack detection through modal analysis, performed an extensive experimental dynamic analysis of free-free beams with the objective of validating theoretical techniques, under development, for the prediction of the location and depth of cracks in straight beams. This paper describes the first part of the authors' work. The experimental techniques used are described and results obtained for various locations and depths of cracks in a straight free-free beam are presented.     

电测深法和电磁波CT法在采空区注浆加固效果检测中的综合应用

本文分别介绍了电测深法和电磁波层析成像方法,两种方法操作简单且能够详细反映采空区注浆加固效果。综合应用两种方法对铁路地下采空区加固效果进行检测,结果均表明了在线路的K0+278～K0+450段加固效果良好,两种检测方法检测结果具有一致性。证明将两种检测方法综合应用在采空区加固效果检测是合理的、可行的,为今后其他同类的检测效果提供了可借鉴的经验。     

EXPERIMENTAL. MODAL. ANALYSIS OF REINFORCED CONCRETE STRUCTURES

Experimental modal analysis techniques have been shown to be applicable to both laboratory test specimens and in situ test structures made of reinforced concrete. These techniques, in general, apply only to linear structures; however, many concrete structures are designed to remain in the linear, uncracked response region during dynamic excitation (nuclear power plant structures, for example). Data from the experimental analyses agreed well with finite-element modal analysis results, and the numerical models were further refined based on the experimental results. Because of the relatively low excitation levels required, these methods provide engineers with techniques for assessing the as-built condition of a structure without introducing damage into the structure. If a concrete structure is damaged, the experimental modal analysis methods could possibly be used to monitor its deterioration.
Further investigations are needed to evaluate the sensitivity to damage of the experimentally determined modal properties. Also, methods must be found to determine, without prior modal data, if an in-situ structure is in a damaged state. These topics are being pursued by other researchers in the experimental modal analysis field.⁶
In its current form, experimental modal analysis methods can provide both practicing and research engineers with a valuable tool for verifying dynamic properties of reinforced concrete structures.