bluuebunny/crossref_metadata_2025 huggingface dataset:
Fractal Theory Based Damage Assessing Method of Acoustic Emission Test
Authors: Huang Yong , Li Hui , Yan Xin , Ou Jin Ping
Published: September 2009

Acoustic emission (AE) test monitoring is an effective non-destructive technique. In the paper, a new damage assessing method which is damage acuteness index for AE signal of PZT patches based on fractal theory was proposed. The damage index was deduced by the character of signal analysed by fractal theory. It is deduced that both the curve length and the fractal dimension (FD) of signal are related with damage development. The AE test of Pseudo-static experiment of a concrete-filled GFRP tubes (CFFT) was performed for validation. The results show that the damage acuteness index can assess damage development process effectively. So the damage acuteness index is a promising method to apply in AE test monitoring.
Detection of Various Damages Based on Piezoceramic Optical Fiber Sensor
Authors: Hong Yong , Wang Gao Ping , Hwang Seung Ho , Kim Hyun Sik , Hong Dong Pyo
Published: September 2009

A piezoelectric ultrasonic sensing system based on an optical fiber has been developed for detection of various damages. The ultrasonic wave generated from a piezoelectric actuator is guided and propagated in the optical fiber and then sensed by a piezoelectric sensor located at the other end of the fiber. The sensed signal can be influenced by environmental and physical changes around the optical fiber. In this study, the sensitivity of the optical fiber sensor is experimentally studied. Various patterns of damage, such as cracks, loosen bolts, holes, are more common forms in real structures. In particular, detection method of the damage with respect to various depths of the crack is presented in this paper.
Applicaton of Modal Filtration for Damage Detection of Rotating Shaft
Authors: Mendrok Krzysztof , Bednarz Jarosław , Uhl Tadeusz
Published: September 2009

The paper describes a modification of the method which uses the modal filtration for damage detection [11] to make it suitable for rotating machinery. Authors have formulated a diagnostic procedure which is based on the output only data measured during object operation. The measurement can be performed both by accelerometers placed on the shaft bearing cages and directly on the shaft with use of the laser vibrometer. The procedure was verified on the experimental data. For the experimental verification authors have used the laboratory stand which allows simulation of different faults.
On Optimal Sensor Placement Criterion for Structural Health Monitoring with Representative Least Squares Method
Authors: Li Dong Sheng , Li Hong Nan , Fritzen Claus Peter
Published: September 2009

A novel sensor placement criterion is proposed for structural health monitoring after five influencing criteria are critically reviewed. The objective of the proposed criterion is to achieve best identification of modal frequencies and mode shapes through almost unbiased estimation of modal coordinates. The proposed criterion derived by the Representative Least Squares method depends on both the characteristics and the actual loading situations of a structure. It selects sensor positions with the best subspace approximation of the vibration responses from the linear space spanned by the mode shapes. Furthermore, the connection between the Effective Independence and the approximate Representative Least Squares estimator is obtained through matrix perturbation analysis. It is found that the Effective Independence is a step-by-step approximation to that of the Representative Least Squares criterion.
Monitoring Vertical Loads on the Bearings of the High Coast Suspension Bridge
Authors: Karoumi Raid , Svedjetun Knut , Gilliusson Staffan
Published: September 2009

Inspections of Sweden’s longest suspension bridge, the approximately ten years old High Coast Suspension Bridge, have shown that the main bridge bearings have been seriously affected by wear. A monitoring program was therefore initiated in 2005 to measure actual vertical loads acting on the bearings as well as the tension in the first hangers of the bridge. This article describes the instrumentation and the calibration process. Interesting results from several months of monitoring are presented. Results show that the measured loads on the bearings due to permanent loads are in very good agreement with what was predicted during design. However, very large loads and large dynamic effects were registered from passing lorries.
The Design of Piezoelectric Transducer for Structural Health Monitoring Using Longitudinal Vibration Modes
Authors: Liu Xing Long , Jiang Zhong Wei
Published: September 2009

Longitudinal vibration mode is conveniently used for damage localization and detection in truss structure. However, a satisfactory piezoelectric impedance response due to longitudinal modes is not so easy to obtain in practical applications. The objective of this paper is to investigate how to obtain the impedance response of longitudinal modes with a piece of PZT transducer. In this case various vibration modes will be excited by unilaterally bonded PZT transducer, so the observation of longitudinal modes becomes complicated. In this paper, the effect of parameters of PZT transducer such as the length and attachment position is discussed in detail. Through selecting a suitable size and attachment position, the impedance response of expected longitudinal modes can be generated. An example for generating impedance peaks of specified longitudinal mode in fixed-fixed beam is given to demonstrate its validity.
Smart Rotating Machines for Condition Monitoring
Authors: Friswell Michael I. , He Yong Yong
Published: September 2009

The concept that changes in the dynamic behaviour of a rotor could be used for general fault detection and monitoring is well established. Current methods rely on the response of the machine to unbalance excitation during run-up, run-down or normal operation, and are mainly based on pattern recognition approaches. Of all machine faults, probably cracks in the rotor pose the greatest danger and research in crack detection has been ongoing for the past 30 years. For large unbalance forces the crack will remain permanently open and the rotor is then asymmetric, which can lead to stability problems. If the static deflection of the rotor due to gravity is large then the crack opens and closes due to the rotation of the shaft (a breathing crack), producing a parametrically excited dynamical system. Although monitoring the unbalance response of rotors is able to detect the presence of a crack, often the method is relatively insensitive, and the crack must be large before it can be robustly detected. Recently methods to enhance the quality of the information obtained from a machine have been attempted, by using additional excitation, for example from active magnetic bearings. This research is directed towards the concept of a smart rotating machine, where the machine is able to detect and diagnose faults and take action automatically, without any human intervention. This paper will consider progress to date in this area, with examples, and consider the prospects for future development.
Condition Monitoring of Textiles Using Optical Techniques
Authors: Ye C.C. , Dulieu-Barton Janice M. , Chambers A.R. , Lennard F.J. , Eastop D.D.
Published: September 2009

In the paper it is proposed to use fibre Bragg grating (FBG) sensors to monitor the deformation and strain in a woven textile. Non-contact digital image correlation (DIC) is used to validate the results. The principal objective of the work in this paper is to identify a suitable adhesive for attaching the FBG sensors to tapestries and textiles. To do this, the interfacial interactions of the optical fibre, the textile material and the necessary adhesive must be considered. The performance of two types of adhesive are studied: a PVA conservation adhesive and a two-part epoxy adhesive Araldite 2015. The effect of the application of the adhesives on the mechanical response of the textile is investigated. Full-field stain maps are obtained from the DIC and are used as the basis to characterise the behaviour of the FBG sensors/adhesive system. The strain transfer coefficients and a reinforcement factor are determined under quasi-static conditions. It is shown that the local reinforcement introduced is more significant in the specimen with the FBG bonded using the Araldite adhesive than those with conservation adhesives. Nevertheless, the Araldite adhesive has a better strain transfer coefficient than the conservation adhesive, although not as high as that expect with conventional engineering materials.
Research on Real-Time Process Monitoring Technology and System for High-Speed Turbopump
Authors: Xia L.R. , Hu Niao Qing , Qin G.J.
Published: September 2009

Turbopump is a high-fault-rate component in Liquid Rocket Engine (LRE). The research on real-time process monitoring technology and system for turbopump is vital to increase the reliability and safety of LRE. In this paper, three real-time process monitoring algorithms for turbopump were studied firstly, on the basis of monitoring parameters selection and multiple domain feature extraction. Then, the real-time monitoring system realized by means of PXI (PCI eXtensions for Instrumentation) controller was introduced. And, aiming at the shortage of the previous system, the real-time process monitoring system based on DSP (Digital Signal Processor) for turbopump was studied to realize higher computing speed, which could conduce to extract multiple domain features and run manifold real-time monitoring algorithms. The new system could also satisfy the small-sized requirement in engine flying state.
The Experimental Research of Delamination Damage Location Based on FBG Sensors Network in Solid Rocket Motor Shell
Authors: Chang Xin Long , He Xiang Yong , Jian Bin , Li Zheng Liang
Published: September 2009

The fiber reinforced composite materials were widely used for aerospace aircrafts and missile weapons, and the delamination was a major problem which reduced the structural integrity and reliability of the solid rocket motor (SRM) composite shell seriously. In order to locate the delamination damage, the fiber Bragg grating (FBG) strain sensors network was embedded in SRM shell, and a multi-step approach of delamination damage location based on strain energy was performed: the strain field was measured in a scatter grid by the FBG strain sensors network in hydraulic testing; then the continuous displacement and strain field was reconstructed with relative sensors data using a moving least square (MLS) mesh-free fitting method; the strain energy of each subregions was calculated from the reconstructed data; finally the damaged subregions was identified successfully by singularity value of strain energy. The results of simulation and experiment indicated that the damage identification and location only required the measure of strain field of the SRM shell, and the presented approach achieved higher accuracy.
Analysis of the Response of a Rotor System Containing a Breathing Crack
Authors: Sinou Jean Jacques
Published: September 2009

The purpose of this paper is to investigate the influence of the presence of transverse cracks in rotors. The dynamic response of the cracked rotor is evaluated by expanding the changing stiffness of the crack (i.e. the breathing mechanism) as a truncated Fourier series and then using the Harmonic Balance Method. The crack detection is based on the use of the 2X and 3X super-harmonic frequency components of the non-linear dynamical behaviour at the associated sub-critical resonant peaks. Various parametric studies including the effects of the crack depth and location, and the crack–unbalance interaction on the dynamic of a crack rotor are undertaken. It will be illustrated that the emerging of super-harmonic frequency components and/or antiresonances can provide useful information on the presence of cracks and may be used on an on-line crack monitoring rotor system for small levels of damage.
Investigation of Condition Monitoring of a Flap System
Authors: Lu F. , Chen Qian
Published: September 2009

This paper presents an initiative research work that applies cointegration testing method to the condition monitoring and fault diagnosis of nonstationary dynamic engineering systems. The cointegration testing method seeks a linear combination of a set of nonstationary system variables which describes the dynamic equilibrium relations among them. The fact that the cointegrational model could be violated on the occurrence of a fault is utilised to detect abnormal conditions. The model residuals are processed and analyzed to extract the fault features. In this paper it is demonstrated that the cointegration testing method is a power full means for condition monitoring for nonstationary engineering systems.
Non-Linear Identification of a RC Element Using Time-Frequency Instantaneous Estimators
Authors: Demarie Giacomo V. , Sabia Donato , Ceravolo Rosario
Published: September 2009

The identification of non-linear systems is an important topic in structural health monitoring of structures undergoing non-stationary behavior. In general, a non-linear or hysteretic response is typical for buildings, bridges, dampers and structural elements not only as a consequence of strong excitations (i. e. earthquake), but also for low to medium loading levels, due to the constitutive behavior of structural elements or joints. This paper focuses on the non-linear identification of a RC beam-column joint, modeled as a SDoF system, subjected to non-stationary loading: the technique used entails the definition of proper instantaneous estimators of the system dynamic properties by using a linear time-varying approximation of the actual system dynamics and representing the structural response in the joint time-frequency domain.
A Steam Turbine Fault Diagnostic System Based on the Web and Database Technologies
Authors: Song Guang Xiong , Gu Yu Jiong , He Yong Yong , Chu Fu Lei
Published: September 2009

The steam turbine is the principal mover in the field of electric power generation. It is very important and necessary to monitor and evaluate the running conditions and diagnose the faults of the steam turbine for the safe and normal running of the electric power plant. Fault diagnosis of the steam turbine is a complicated process and requires high level of the expertise. In order to significantly reduce the cost consumed in the fault diagnosis, increase the consistency of diagnosing decision-making, and better utilize the turbine’s management information resource, in this paper, an integrated Web-based expert system of the fault diagnosis for general purpose has been developed for the steam turbine of a power station. Moreover, it can be regarded as an advisory tool to those field engineers having much technical experience and as a training tool to less-experienced personnel who need guidance and advice.
This paper describes a research project aiming to develop a web-based intelligent diagnostic system for the steam turbine, and discusses the process of the fault diagnosis and the issues involved in developing the system. The paper also includes several practical issues related to the architectures of the intelligent web-based applications. The system is built on a three-tier architecture, including the following components: knowledge base, inference engine, knowledge administration interface, user interface, knowledge administration, and integrated database. The diagnostic system employs heuristic rules to diagnose the steam turbine faults.
Sensor Triangulation for Damage Localisation in Composite Plates
Authors: Kudela Pawel , Ostachowicz Wiesław M. , Zak Arkadiusz
Published: September 2009

The aim of this paper is development of an algorithm for damage localisation in composite plates based on wave propagation signals registered by sensors. It is proposed to distribute the sensors uniformly over the area of a plate-like structure performing triangulation. Next the registered signals are processed and a damage influence map is created in each triangle separately in order to avoid problems connected with reflections from boundaries of the structure. The proposed procedure has been verified on numerical signals as well as experimental signals.
Diagnose and Analysis of Coupling Faults on Nonlinear Rotor-Bearing-Seal System Prediction
Authors: Liu Shu Lian , Li An , Zheng Shui Ying
Published: September 2009

The fluid-solid coupling analysis of the nonlinear rotor-bearing system with labyrinth seal was presented. The dynamic equations of rotor-bearing system were built up by combining d’Alemdert principle with Rize way, then the nonlinear oil film forces based on steady short bearing model, unbalanced excitation forces and gas excitation forces calculated by FLUENT could be coupled to system. Such nonlinear equations were numerically solved by Newmark integration method. The dynamics and the representation characteristics were investigated through a lot of numerical calculations, then the occurrence and development mechanism of the different coupling faults revealed based on the results of numerical calculation. The severity and mutation of some faults were also studied.
Fault Recognition Method of Rolling Bearings Based on Volterra Series and HMM
Authors: Jiang Jing , Li Zhi Nong
Published: September 2009

A new bearing fault recognition method based on volterra series and HMM is proposed. In the proposed method, first the feature vectors are extracted from amplitude demodulated signals obtained from normal, ball, inner and outer faulty bearings. The feature vectors are based on the volterra series of the vibration signals, which is obtained by the subspace method. Then these feature vectors are input to each fault’s HMM to be recognized. The result of experiment shows that the proposed method is very effective. The proposed method is tested with the experiment data sampled from drive end ball bearing of an induction motor driven mechanical system.
A Novel Fault Diagnosis Method Using PCA and ART-Similarity Classifier Based on Yu’s Norm
Authors: Xu Zeng Bing , Xuan Jian Ping , Shi Tie Lin , Wu Bo , Hu You Min
Published: September 2009

In this paper, a novel similarity classifier which synthesizes the adaptive resonance theory (ART) and the similarity classifier based on the Yu’s norm is proposed. The proposed ART-similarity classifier can not only carry out training without forgetting previously trained patterns but also be adaptive to changes in the environment. In order to test the proposed classifier, it is applied to the fault diagnosis of rolling element bearings. Before application to the fault diagnosis of bearings, considering computation burden principal component analysis (PCA) is proposed to reduce the number of features. The PCs are input the proposed classifier to diagnose the faulty bearings. The experiment results testify that the proposed classifier can identify the faults accurately. Furthermore, in order to validate the effectiveness of the proposed classifier further, it compares with other neural networks, such as the fuzzy ART, self-organising feature maps (SOFMs) and radial basis function (RBF) neural network through diagnosing the bearings under the same conditions. The comparison results confirm the superiority of the proposed method.
Wavelet Selection for Bearing Defect Diagnosis
Authors: Yan Ru Qiang , Gao Robert X.
Published: September 2009

This paper introduces a quantitative measure based on the energy-to-Shannon entropy ratio for base wavelet selection in vibration signal analysis. The Gaussian-modulated sinusoidal signal and a realistic vibration signal measured from a ball bearing have been used to evaluate the effectiveness of the measure. Experimental results demonstrate that the wavelet selected using the developed measure is effective in diagnosing structural defects in the bearing and the method developed provides systematic guidance in wavelet selection.
Shaft Crack Analysis and Diagnosis for the 600MW Steam Turbine Generator
Authors: Jiang Dong Xiang , Hong Liang You , Huang Qian
Published: September 2009

In order to find the cause of the shaft crack appeared in a 600MW steam turbine generator, several measurements are taken. The shaft assembly consists of three parts: shrink-fitted coupling, shaft and key which are used to transfer torque between coupling and shaft. First, the natural frequency of the shaft system is calculated. The result shows that the vibration signal contains the frequency nears the second natural frequency of the steam turbine shaft system. Second, stress field near the damaged coupling and shaft is analyzed using finite element method. The torque under different operation condition is calculated before stress analysis and applied to the shaft assembly, then. And, local stress concentrations position calculated is proved to be coincident with the place crack initiation. Finally, the cause of the fault is analyzed: at least three causes have found to be having something to do with the crack fault.
Experimental Investigation of Pedestal Looseness in a Rotor-Bearing System
Authors: Lu Wen Xiu , Chu Fu Lei
Published: September 2009

An experimental setup of rotor-bearing system is installed and vibration characteristics of the system with pedestal looseness are investigated. The pretightening bolt between the bearing house and pedestal is adjusted to simulate the pedestal looseness fault. The vibration waveforms, spectra and orbits are used to analyze the nonlinear response of the system with pedestal looseness. Different parameters, including speed, looseness gap, imbalance mass and disk position are changed to observe the nonlinear vibration characteristics. The experiments show that the system motion generally contains the 1/2X fractional harmonic component and multiple harmonic components such as 2X, 3X, etc. Under some special conditions, the pedestal looseness occurs intermittently, that is, occurs in some periods and doesn’t in other periods.
Signal Processing by Energy Normalization Method Based on Wavelet Packet
Authors: Chen Tao , Xu Xiao Li , Wang Shao Hong
Published: September 2009

Fault diagnosis is a key technology to ensure safe and reliable operation of large electromechanical equipments. Fault feature extraction is important in fault diagnosis process. For non-stationary vibration signal, energy normalization method based on wavelet packet is used to make signal processing with signals decomposed into different frequency bands to perform energy normalization process in corresponding frequency band so as to extract fault feature. Flue Gas Turbine is chosen as research object and analysis shows that energy normalization processing method based on wavelet packet can effectively extract non-stationary signal characteristic parameters and make effective nondestructive testing analysis of equipments condition.
Application of Cyclic Correlation Analysis to Gear Damage Detection
Authors: Feng Zhi Peng , Zuo Ming J. , Hao Ru Jiang , Chu Fu Lei
Published: September 2009

The cyclic autocorrelation function is used with regard to the cyclostationarity of gear vibrations in order to extract the modulation features of gearbox vibration signals, and to detect localized gear damage. The properties of the amplitude and frequency modulated signals in the cyclic frequency domain are summarized in order to investigate the differences between the modulation features of normal and faulty gearbox vibration signals. Gear tooth spalling is detected by the presence of many sidebands in a zero-lag time-slice of the cyclic autocorrelation function, thereby indicating an increase in the degree of modulation effect. The damage source is located by the spacing of the sidebands.
Identification of Small Crack in Beam Structures Using Anti-Resonant Frequency and Wavelet Analysis
Authors: Wang Dan Sheng , Shen Dan Yan , Zhu Hong Ping
Published: September 2009

Structural crack identification has been received considerable attention in recent decade. A lot of different techniques like acoustic emission, ultrasonic, or X-ray, etc have been used for structural crack detection. However, it is still difficult to identify the small crack in structures. A new method for identification of small crack in beam structures using the first anti-resonant frequency curve is proposed in this paper. The method makes use of the driving-point mechanical impedance characteristics of beam structures and a simplified rotational spring model to model the edge crack of beam. After the first anti-resonant frequency curve is obtained, signal process based on wavelet transformation will be carried out and the small crack in beam structures can be explored. The proposed method is validated by a numerical example of cracked beam with pinned-pinned or fixed-free boundary. It is concluded that not only the location of beam crack can be determined, but also the extent of crack damage can be identified qualitatively based on the first anti-resonant frequency curve and wavelet analysis.
Diagnosis of Rolling Elements Bearing Based on Inverse Autoregressive Filter
Authors: Garibaldi Luigi , Wang Guo Feng , Marchesiello Stefano , Fasana Alessandro
Published: September 2009

Diagnosis of rolling elements bearing plays an important role on the running and maintenance of mechanical equipments. To enhance the feature of fault and to further diagnose the status of bearings with a small fault size so as to realize the early recognition, the method of inverse filter based on Autoregressive model is presented in this paper, and the corresponding criterion of order selection is also discussed. Analysis of simulation signals and real data show that this method could enhance feature of impulse signal. Meanwhile, it is also found that for small size fault, the root mean square feature is more effective than kurtosis value, which is considered very useful for early diagnosis of rolling elements bearings.
Time-Varying Output-Only Identification of a Cracked Beam
Authors: Bellino A. , Garibaldi Luigi , Marchesiello Stefano
Published: September 2009

In this paper a time-varying identification method is presented, in order to detect the presence of an open crack in a beam with a moving mass travelling on it. The ratio between the considered moving mass and the total mass of the beam is high, thus the identified modal frequencies of the whole structure are time-varying. This situation often occurs when considering the dynamic interaction beetween a train and a bridge and specific identification tools must be used. It is shown that the identification method, referred to here as Short-Time Stochastic Subspace Identification, can give information about the presence of damage in case of time-varying systems.
Defects Diagnosis of Bearing by Means of Acoustic Emission and Continuous Wavelet Transform
Authors: Hao Ru Jiang , Feng Zhi Peng , Chu Fu Lei
Published: September 2009

The acoustic emission signals of rolling bearing with different type of defects are de-noised and illustrated by the continuous wavelet transform and scalogram. Morlet wavelet function is selected and the wavelet parameters are optimized based on the principle of minimal wavelet entropy. The soft-threshold de-noising is used to filter the wavelet transform coefficients. The de-noised signals obtained by reconstructing the wavelet coefficients show the obvious impulsive features. Based on the optimized waveform parameters, the wavelet scalogram is used to analyze the real AE signal from the defective rolling bearing in experimental test rig. The results indicate that the proposed method is useful and efficient for signal purification and features extraction.
Particle Swarm vs. Evolutionary Optimization Techniques in a Multiobjective Framework for Damage Identification
Authors: Perera Ricardo , Fang Sheng En , Ruiz Antonio
Published: September 2009

In the context of real-world damage detection problems, the lack of a clear objective function advises to perform simultaneous optimizations of several objectives with the purpose of improving the performance of the procedure. Evolutionary algorithms have been considered to be particularly appropriate to these kinds of problems. However, evolutionary techniques require a relatively long time to obtain a Pareto front of high quality. Particle swarm optimization (PSO) is one of the newest techniques within the family of optimization algorithms. The PSO algorithm relies only on two simple PSO self-updating equations whose purpose is to try to emulate the best global individual found, as well as the best solutions found by each individual particle. Since an individual obtains useful information only from the local and global optimal individuals, it converges to the best solution quickly. PSO has become very popular because of its simplicity and convergence speed. However, there are many associated problems that require further study for extending PSO in solving multi-objective problems. The goal of this paper is to present the first application of PSO to multiobjective damage identification problems and investigate the applicability of several variations of the basic PSO technique. The potential of combining evolutionary computation and PSO concepts for damage identification problems is explored in this work by using a multiobjective evolutionary particle swarm optimization algorithm.
Damage Identification Using Response Surface Methodology
Authors: Fang Sheng En , Perera Ricardo
Published: September 2009

As a combination of statistical and mathematical techniques, response surface
methodology gives explicit functions to express the relationship between the inputs and outputs of a
physical system. This methodology has been widely applied to design optimization, response
prediction and model validation but so far little literature related to its application in structural
damage identification has been found. Therefore this paper presents a systematic damage
identification procedure consisting of four steps of feature selection, parameter screening, primary
response surface modeling and updating, reference-state response surface modeling with damage
identification realization. 2k factorial design and central composite design are adopted to construct
response surface models for parameter screening and model updating purposes, respectively. The
proposed method is verified against an experimental reinforced concrete frame and it is found that the
proposed method works well in damage prediction.
Simulations of a Dual-Rotor System with Local Rub-Impacts Based on Rigid-Flexible Multi-Body Model
Authors: Han Qing Kai , Luo Hai Tao , Wen Bang Chun
Published: September 2009

The nonlinear dynamical analyses of a dual-rotor system of an aero-engine are investigated with considering local rub-impacts based on rigid-flexible multi-body simulations. The dual-rotor system is set up from a practical aero-engine prototype, which includes an inner shaft (lower-pressure shaft) and an outer shaft (higher-pressure shaft). The two shafts are in internal-external arrangement and connected by six different rolling bearings. Firstly, a rigid-flexible multi-body model of the dual-rotor system with local rub-impacts is established with MSC.Adams. Then, for the rub-impacts happening between the higher-pressure disk and the fixed elastic rod, the rub-impact forces are described as a nonlinear one with piecewise stiffness and a constant friction. At last, the transverse vibrations of the dual-rotor system are simulated. From the obtained frequency spectra and shaft center orbits of given shaft nodes, many of them are composed of multi-frequencies and demonstrate nonlinear motion patterns.
Spectral Element Modelling of Wave Propagation and Impedance Based SHM Systems
Authors: Schulte Rolf T. , Xing Ke Jia , Fritzen Claus Peter
Published: September 2009

In recent years many SHM approaches based on elastic waves that are generated and sensed by surface-bonded piezoelectric patches have been developed. Some of those utilize wave propagation phenomena; others use changes in the electromechanical impedance to detect structural damage. The capability of most approaches strongly depends on adequate choice of SHM system parameters like excitation signals and actuator/sensor types and positions. For this reason there is a growing interest in efficient and accurate simulation tools to shorten time and cost of the necessary tedious pretests.
To detect small damage generally high frequency excitation signals have to be used. Because of this a very dense finite element mesh is required for an accurate simulation. As a consequence a conventional finite element simulation becomes computationally inefficient. A new approach that seems to be more promising is the time domain spectral element method.
This contribution presents the theoretical background and some results of numerical calculations of the propagation of waves. The simulation is performed using the spectral element method (SEM), which leads to a diagonal mass matrix. Besides a significant saving of memory this leads to a crucial reduction of complexity of the time integration algorithm for the wave propagation calculation.
A new approach to simulate the E/M impedance using time domain spectral elements is shown. An example demonstrates a good correlation of simulation and measurement data, so that the proposed simulation methodology seems to be a promising tool to make impedance based SHM systems more efficient, especially regarding the necessary parameter studies.
Experimental Verification and Comparison of Mode Shape-Based Damage Detection Methods
Authors: Radzieński Maciej , Krawczuk Marek , Ostachowicz Wiesław M.
Published: September 2009

This paper presents experimental verification and comparison of damage detection methods based on changes in mode shapes such as: mode shape curvature (MSC), modal assurance criterion (MAC), strain energy (SE), modified Laplacian operator (MLO), generalized fractal dimension (GFD) and Wavelets Transform (WT). The object of the investigation is to determine benefits and drawbacks of the aforementioned methods and to develop data preprocessing algorithms for increasing damage assessment effectiveness by using signal processing techniques such as interpolation and extrapolation measured points. Noise reduction algorithms based on moving average, median filter and wavelet decomposition are also tested. The experiments were performed on a 1m long steal cantilever beam. Damage was introduced in form of 10% and 20% deep saw cut, placed in 10%, 30%, 50%, 70% and 90% beam length. Measurements were made using non-contact Scanning Laser Doppler Vibrometer at 125 points equally spaced along beam length.
Modal Identification of an Experimental Model of Masonry Arch Bridge
Authors: Ruocci Gianluca , Ceravolo Rosario , de Stefano Alessandro
Published: September 2009

The erosion of the river bed material at bridge pier foundation produced by scour events is one of the main causes of the observed masonry bridges failures and collapses. Foundation settlements and rotations derived from the reduction of the footprint under the piers threaten masonry arch bridges integrity more than any gravity load. The resulting effect on the structure is the development of cracking mechanisms on the arches which may affect the dynamic behaviour of the whole bridge. A scaled experimental model of a masonry arch bridge has been built in the laboratory of the Dep. of Structural Engineering at the Politecnico di Torino. The aim was to better understand scour damage scenario and to identify early structural symptoms of pier erosion. A preliminary dynamic identification is carried out on the intact structure and a comparison with the FEM results is performed. The set of identified modal parameters is adopted as the reference system that will be compared with those acquired after the application of damage of increasing extent.
Study and Application of Grey System Theory for Fatigue Life Prediction
Authors: Wang Xu Liang , Nie Hong , Jiang Quan
Published: September 2009

The complexity of fatigue phenomenon results in the difficulty of fatigue life prediction. The fatigue phenomenon is treated as being in a grey system. By using of grey system theory, a new method for fatigue life prediction based on grey model GM(1,1) is proposed. Results of the example show that the prediction error can be reduced from 61.55% to 24.32%, and the prediction is on the safe side. Therefore, it is proved that the method is practical and useful for fatigue life prediction in engineering.
Life Prediction of Stainless Steels under Creep-Fatigue
Authors: He Xiao Cong
Published: September 2009

The aim of this study is to investigate the creep-fatigue behavior of stainless steel materials. Based on the elevated-temperature tensile, creep and rupture test data, thermal creep-fatigue modelling was conducted to predict the failure life of stainless steels. In the low cycle thermal fatigue life model, Manson’s Universal Slopes equation was used as an empirical correlation which relates fatigue endurance to tensile properties. Fatigue test data were used in conjunction with different modes to establish the relationship between temperature and other parameters. Then creep models were created for stainless steel materials. In order to correlate the results of short-time elevated temperature tests with long-term service performance at more moderate temperatures, different creep prediction models, namely Basquin model, Sherby-Dorn model and Manson-Haferd model, were studied. Comparison between the different creep prediction models were carried out for a range of stresses and temperatures. A linear damage summation method was used to establish life prediction model of stainless steel materials under creep-fatigue.
Fatigue Damage Evaluation and Retrofit of Steel Orthotropic Bridge Decks
Authors: Wang Chung Sheng , Feng Ya Cheng , Duan Lan
Published: September 2009

Since the first application of steel orthotropic deck in bridges, engineers have shown great interest in the popularization of steel decks, based on their various advantages like light-weight, high capacity and so on. However, because of their complex configurations, repeated loading, and stress concentration, many details of steel orthotropic bridge decks are fatigue-sensitive. Recently, considerable increase in traffic volume and wheel loads has caused a number of fatigue cracks in steel orthotropic bridge decks in China. For example, bridge engineers have detected thousands of fatigue cracks in steel orthotropic deck on the main box girder of Humen Bridge only ten years after opening to traffic, which is the first modern suspension bridge with the main span of 888 meters in China. So the bridge owners pay more attention to evaluate the locations of fatigue damages. In current paper, the standard section of the real bridge deck was simulated and a kind of typical fatigue cracks was selected to analyze their fatigue life using S-N curve, the fatigue damage analysis was carried out on the longitudinal ribs to deck plate connections. The fatigue damage analysis results were consistent with the observations from real bridge decks.
Fatigue Safety Evaluation of Existing Reinforced Concrete Bridges
Authors: Wang Chung Sheng , Dong Xiao Hong , Miao Wen Hui , Li Gan
Published: September 2009

Generally, fatigue has not been considered as a key problem in the design of reinforced concrete bridges. Until the 1960s, reinforcement was mild steel and the stresses permitted in the steel bar and the concrete were such that fatigue and fracture failure was believed to be impossible. With the developments of reinforced concrete structures, higher working stresses were permitted and, in particular, high yield reinforcing bars were introduced. Design rules were issued to control cracking and to prohibit welding of reinforcement unless the risk of fatigue was negligible. In recent years, great deals of researches have been carried out, leading to a better understanding of the fatigue behaviors in concrete structures. Some studies showed that fatigue could occur in reinforced concrete structures in combination with other causes of deterioration. In the past eight years, considerable increases in traffic intensity and wheel loads have caused obviously fatigue damage in reinforced concrete structures in China. Some reinforced concrete bridges were damaged seriously, leading to the whole bridge collapse sometimes because of overloading and oversize trucks. So how to evaluate the fatigue safety of existing reinforced concrete bridges is an urgent problem in China. In the current paper, the assessment models of existing reinforced concrete bridges based on S-N curve and fracture mechanics approach were proposed considering the effect of overloading and oversize trucks. Finally the assessment method based on S-N curve and in-situ monitoring data was applied to a case study bridge.
Fatigue Properties Assessment of Corroded Cable
Authors: Lan Cheng Ming , Li Hui
Published: September 2009

Based on fatigue test results of corroded wires obtained from dissection of actual parallel wire cables which were used on a certain domestic cable-stayed bridge, the fatigue properties of corroded parallel wire cable are investigated by the method of Monte Carlo simulation in this paper. The results of fatigue life and corrosion degree of corroded wire are presented. Comparisons between the original design information and fatigue test results, it can be seen that corrosions make the fatigue lives of wires decreasing sharply. The fatigue life of individual wire is described by Weibull distribution considered some useful parameters such as, stress range, mean stress, mean static strength and length effects. The effects of percentage of broken wire, cable S-N curve parameter on cable fatigue life are discussed. It can be seen that the cable fatigue lives are controlled by a small fraction of the cable wires with the shortest fatigue lives. Finally, the S-N curves of cable are calculated by Monte Carlo simulations based on the results of individual wire fatigue test, and compared with the results of cable fatigue test.
Influence of Disbond Defects on the Dispersion Properties of Adhesive Bonding Structures
Authors: Chang Xin Long , Ni Tao , Ai Chunan
Published: September 2009

With increasing application of adhesive bonding structures, the quality assessment of adhesive bonding became critical. Ultrasonic approach was an acknowledged promising method in many Nondestructive testing (NDT) techniques. The research object was to use analytical models to develop a quantitative understanding of the affections in different situations on the dispersion properties. An improved global matrix method was introduced to compute the dispersive curves, which can effectively eliminate the instability for thicker layers and higher frequencies. In order to evaluate the disbond defect, the cohesive strength degradation mode and the spring mode were then adopted to describe the cohesive failure and the interface failure, respectively. In the paper, cohesive failure, interface failure and mixed failure were analyzed for the steel/adhesive layer/insulation layered structure. Interface failure induced the modes of multilayer structure to regress to the modes of single layers, while the cohesive failure made the dispersive curves move to the lower frequency direction, and changing the relative position of spring layer led the dispersive curves shift to the higher frequency direction. Among all the factors, the interface failure was dominant. Finally, the variety of the dispersive modes in a special frequency band (1~1.5MHz) was found that can be regarded as parameters of the adhesive bonding quality.
Integrity Strain Response Analysis of a Long Span Cable-Stayed Bridge
Authors: Li Shun Long , Li Hui , Ou Jin Ping , Li Hong Wei
Published: September 2009

This paper presents the analysis of strain time histories measured by structural health monitoring system. The main objective of this study is to prepare data for reliability estimation of main components as well as the entire structural system. The strain and corresponding temperature data is collected at the following stages: closure segment reconstruction stage and operating stage. The strain monitoring of the closure segment during the reconstruction stage provided valuable information on early-life strain development and reference characteristics for events such as post tensioning and temperature change. These lessons learnt from the reconstruction monitoring can be used for understanding subsequent bridge behavior, including damage detection and reference points of subsequent monitoring. Specially, the loading test results reveal the effectiveness and correctness of the strain acquiring system and provide evidence for reliable long-tem monitoring. Strain and temperature data have been recorded at sampling frequency of 62.5Hz since loading test, which would provide information linear stress-strain relationships. The long-term creep and shrinkage model were provided by Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridge and Culverts (JTG D62-2004). Through the statistical analysis of the online strain response, the probability model of long-term performance under environmental and random traffic loading are obtained which gives the potential of its application of reliability based assessment on cable stayed bridges where they evaluated the reliability of elements such as cables and stiffening girder.
Updating of Finite Element Model in Considering Mode Errors with Fuzzy Theory
Authors: Liu Yang , Duan Zhong Dong , Li Hui
Published: September 2009

Finite element model updating aims at reconciling the analytical model with the test one, to acquire a refined model with high-fidelity in structural dynamic properties. However, testing data are inevitable polluted by noises. In this study, the mode parameters and design variables are modeled as fuzzy variables, and a fuzzy model updating method is developed. Instead of a single optimal model, a set of satisfactory models is obtained. The most physically compatible solution is sorted by insights to the structures. The proposed method is applied to a real concrete bridge, for which a physically meaningful model is identified.
Damage Localisation in Thin Panels Using Elastic Wave Propagation Method
Authors: Wandowski Tomasz , Malinowski Pawel , Ostachowicz Wiesław M.
Published: September 2009

In this paper algorithm for damage localisation in thin panels made of aluminium alloy has been proposed. Mentioned algorithm uses Lamb wave propagation methods and geometrical approach for damage localisation. Elastic waves are generated and received using piezoelectric transducers. Excited elastic waves propagate and reflect from panel boundary and discontinuities existing in the panel. Wave reflection can be registered through the piezoelectric transducers and used in signal processing algorithm. Processing algorithm consists of two parts: signal filtering and extraction of damage location. The first part is used in order to remove noise from received signals. Second part allows to extract arrival time of waves reflected from discontinuity, very often called Time Of Flight (TOF). Localisation algorithm uses pairs of transducers from a concentrated transducers configuration. Using signals from pair of transducers two times of reflection can be extracted from received signals. Because coordinates of transducers are well known ellipse can be constructed based on extracted times of waves reflections. Damage lies one ellipse but it is not known exactly where. Therefore one ellipse is not enough to localise a discontinuity. In order of proper damage localisation more ellipses must be used. In this purpose signals received by larger number of transducers pairs are used in damage localisation algorithm. Points of ellipses intersections allow to indicate localisation of damage. Described signal processing algorithm has been coded in the MATLAB® environment. In this work experimental results has been presented.