Key Engineering Materials Vols. 293-294

Abstract: Certain results have been presented in this work on damped non-linear vibration of a delaminated composite beam. In order to investigate this problem the finite element method has been applied while for beam modelling higher order shear deformation beam finite elements have been used. The vibration of the beam has been investigated in the time domain and next the time series obtained from solving the non-linear equation of motion have been analysed in the frequency domain by using FFT. The vibration responses of the beam due to various harmonic excitations, at different delamination locations, and for different delamination lengths, together with changes in the dissipation of damping energy due to the delamination, have all been considered in the work.

Abstract: The detection and characterisation of subsurface flaws in nonmetallic materials are very important for people’s health, lives, and environment. Possible damage must be detected early and reliably. A capacitive approach for detecting the subsurface cracks is discussed. A uniplanar capacitive sensor with multi-electrodes for obtaining the corresponding electrical capacitance information of the measured slab is presented. An experimental rig, which is composed of a uniplanar capacitive sensor of 8-electrodes and two engineering plastic samples, has been built for damage detection of nonmetallic material. Principal component analysis is used to extract relevant features from capacitance values for damage detection and identification. The simulated, as well as the preliminary experimental results show that the current approach is capable of detecting subsurface damages of nonmetallic materials and discriminating the flaws. The proposed approach is feasible and effective for damage detection and health monitoring.

Abstract: So far, the inspection of building structures and especially of bridges is mainly done visually. Therefore, the condition of the structure is examined from the surface and the interpretation and assessment is based on the experience of the expert. However, the main purpose of monitoring civil structures is not to substitute visual inspection. Continuous structural health monitoring should provide data from the inside of a structure to better understand its structural performance and to predict its durability and remaining life time. Monitoring should render objective data and observable alterations in the structure continuously, which cannot be done by visual inspection. More detailed information is needed with respect to different exposure due to dynamic and static loads and also temperature and moisture. Today mainly wired monitoring systems are used to monitor structures, which are relatively expensive and time consuming to install. In this paper the basic principle of a wireless monitoring system equipped with MEMS sensors is presented, which can be easily installed at different structures. Microelectromechanical systems (MEMS) are small integrated devices or systems that combine electrical and mechanical components. A wireless monitoring sensor network equipped with such MEMS could be produced with a very low budget and becomes very efficient. This permits a wide area of applications not only in civil engineering. With respect to different applications relevant properties of a wireless monitoring system are described. In detail network configuration, power consumption, data acquisition and data aggregation, signal analysis and data reduction as well as reliability and robustness are discussed.

Abstract: Power transformers’ failures carry great costs to electric companies. To diminish this problem in four working 40 MVA transformers, the authors have implemented the measurement system of a failure prediction tool, which is the basis of a predictive maintenance infrastructure. The prediction models obtain their inputs from sensors, whose values must be conditioned, sampled and filtered before feeding the forecasting algorithms. Applying Data Warehouse tech- niques, the models have been provided with an abstraction of sensors the authors have called Virtual Cards. By means of these virtual devices, models have access to clean data, both fresh and historic, from the set of sensors they need. Besides, several characteristics of the data flow coming from the Virtual Cards, such as the sample rate or the set of sensors itself, can be dynamically reconfigured. A replication scheme was implemented to allow the distribution of demanding processing tasks and the remote management of the prediction applications.

Abstract: A new model of impedance-based structural health monitoring (SHM) using the spectral element method (SEM) and electric circuit analysis has been developed. This model provides additional information for more accurately identifying and locating damage and in designing the SHM system. Complex functions of the SHM system such as estimation of remaining life are also made possible with the use of the model. The circuit analysis can be applied to any type of structural model. However, since impedance-based SHM relies on high frequency excitation of the structure using piezoelectric patches, finite element modeling may not be applicable and instead the spectral element method (SEM) is used. SEM more accurately models higher frequency vibrations since the mass is modeled “exactly” and incorporates higher order models more easily. Model and experimental results are presented for damaged and undamaged specimens.

Abstract: Machine field services depend on sensor-driven management systems that provide alerts, alarms and indicators. At the moment the alarm is sounded, it’s sometimes too late to prevent the failure. There is no alert provided that looks at degradation over time. If we could monitor degradation, then we would forecast upcoming situations, and perform maintenance tasks when necessary. In our research we chose to focus on intelligent maintenance system, which is defined as the prediction and forecast of equipment performance. Predictive maintenance, on the other hand, focuses on machine performance features. Data come from two sources: sensors mounted on the machine to gather the machine feature information, and information from the entire manufacturing system, including machine productivity, past history and trending. By correlating data from these sources — current and historical — predictions can be made about future performance. In this article case study of coal mining machinery health prediction is presented. Health of water pumping unit was considered. Such units placed in old mine shafts are crucial to avoid flooding working ones. As an effect of predictive maintenance it can be possible to improve safety and reduce costs incurred from accidents.

Abstract: A methodology of defect identification in linear DC circuits based on so called Virtual Distortion Method (VDM) will be presented. The proposed approach takes adventage of the analogy linking mechanical models of truss structures and electric circuits. In this paper we cover the issue of modelling defects in electric circuits by compatible state of distortions, next we introduce the concept of influence matrix Dij, which describes global sensitivity of the circuit and enables fast recalculation of system response, and we formulate a gradient method of defect identification (inverse problem) based on local current and voltage measurements. In the following analysis we focus on so-called impotent states of distortions, which are the source of ambiguity of solution. We show that these difficulties can be overcome by a proper measuring strategy.

Abstract: The paper pursues the exploration of the feasibility and reliability of current damage detection technologies, evaluating their detection capabilities, environmental factors effects, false alarms rate, adaptability to complex geometries, etc. The method to be used is based on finite element modal updating. Three aspects, as outlined below, are covered: testing samples will be aluminium sheets (0.6m x 0.4m x 1.6mm) strengthened with riveted L-shaped stiffeners. Data will be presented from the undamaged specimens. Secondly, the testing of the samples with damage simulated at different places by temporary removal of specific rivets, thus affecting the overall structural characteristics of the structure. The models used for damage identification methods will be fine tuned to properly detect the simulated damages. Finally, using this information, the paper resumes the capabilities of the method to detect and locate the simulated damage.

Abstract: According to the characteristics of anti-explosion analysis about the small cylindrical shell structure under water, in which the wave scattering is so great that it cannot be ignored, an approximate procedure is proposed to analyze the shock load of the structure suffered underwater explosion. The shock wave is decomposed as the summation of plane harmonic waves with various frequencies, then the scattered acoustic field around the cylindrical structure is studied, by which the overall pressure distribution on the surface of the structure can be obtained. The average overall pressure of the structure suffered underwater explosion can be calculated also, which can be considered as the underwater explosive load. An underwater explosion trial is done in a lake to validate the proposed procedure, and the results show that the overall pressure distribution on the surface predicated by the procedure theoretically nicely agree with the results of trial. Then, the time history of stresses from the trial is quite close to that from numeric simulation. The procedure is understood easily, and can be applied in analyzing the time history of stresses of small cylindrical structures impacted by shock wave, in which the wave scattering of structures plays a key part.