Key Engineering Materials Vol. 518

Abstract: The modal filter has various applications, among the others for damage detection. It was shown, that a structural modification (e.g. drop of stiffness due to a crack) causes an appearance of peaks on the output of the modal filter. This peaks result from not perfect modal filtration due to system local structural changes. That makes it a great indicator for damage detection, which has fallowing advantages: low computational afford due to the data reduction, the structural health monitoring system based on it, is easy to automate. Furthermore the system is theoretically insensitive to environmental changes as temperature or humidity variation (global structural changes do not cause a drop of modal filtration accuracy). In the paper the practical implementation of the presented technique is shown. The developed structural health monitoring (SHM) system is described as well as results of its extensive simulation and laboratory testing. Finally the application of the system for the structural changes detection on the airplane parts is presented..

Abstract: This paper is concerned with reporting some recent developments in Structural Health Monitoring (SHM) research conducted within the Dynamics Research Group at the University of Sheffield. The particular developments discussed are concerned with arguably the two main problems facing data-based approaches to SHM, namely: how to obtain data from damage states of a structure for supervised learning and how to remove environmental and operational effects from data when unsupervised learning (novelty detection) is indicated.

Abstract: New generations of offshore wind turbines are playing a leading role in the energy arena. One of the target challenges is to achieve reliable Structural Health Monitoring (SHM) of the blades. Fault detection at the early stage is a vital issue for the structural and economical success of the large wind turbines. In this study, experimental measurements of Frequency Response Functions (FRFs) are used and identification of mode shapes and natural frequencies is accomplished via an LMS system. Novelty detection is introduced as a robust statistical method for low-level damage detection which has not yet been widely used in SHM of composite blades. Fault diagnosis of wind turbine blades is a challenge due to their composite material, dimensions, aerodynamic nature and environmental conditions. The novelty approach combined with vibration measurements introduces an online condition monitoring method. This paper presents the outcomes of a scheme for damage detection of carbon fibre material in which novelty detection approaches are applied to FRF measurements. The approach is demonstrated for a stiffened composite plate subject to incremental levels of impact damage.

Abstract: The interest in composite repair technologies has been recently increased following the wide applications of composite materials in aerospace industry. Bonded patch repair technologies provide an alternative to mechanically fastened repairs with significantly higher performance. Scarf repairs offer great advantages compared to external patch repairs since they provide higher stiffness by matching ply to ply the original structure and by reducing stress discontinuities in the repaired region. Ultrasonic guided waves have been extensively used for the health monitoring of complex structures due to their remarkable ability of defect recognition. The authors have previously investigated the extraction of the instantaneous characteristics of Lamb waves for the monitoring of an aluminium repaired structure, highlighting the potential use of such waves in the inspection of repaired structures [1]. In the current study, the behaviour of a scarf repair was monitored with guided ultrasonic waves excited by low profile, surface bonded piezoceramic transducers under longitudinal tensile loading. Appropriate damage indices were extracted and the results were correlated with images taken through a 3-Dimensional Digital Image Correlation (3-D DIC) technique. The correlation of the extracted features with the early stage damage is performed and conclusions about the recovered strength through the scarf repair are deduced. Finally the study compares results obtained from the on-line analysis and from off-line techniques such as ultrasonic C-scanning and X-ray radiography.

Abstract: In the paper the vision-based method of civil engineering constructions in-plane deflection measurement and state monitoring is presented. The displacement field of the analyzed structure resulting from a load was computed by means of the digital image correlation coefficient. The application of homography mapping enabled the deflection curve to be computed from two images of the construction acquired from two distinct points in a space. There developed methodology, created software tool as well as experimental results obtained from tests made on lab set-ups and a civil engineering construction are investigated. The experiments are carried out on the lab setup consisting of SRL high resolution digital cameras and the steel frame loaded by a point force. The vision based method results are compared with other contact and non-contact measurement techniques. The deflection of the tram viaduct is investigated and results are compared with the data obtained by the interferometric radar.

Abstract: The active support of a large-scale structure, made up of two elements was designed and manufactured. The first of them - piezoelectric actuator, enables the simulations of vibrations transferred from the ground to the structure. In order to minimize vibrations transmitted through the ground to the construction, the second element of the active support - a system based on magnetorheological dampers was used. The active support enables the simulations of vibrations from the ground using a piezoelectric stack controlled in a reverse feedback loop. Control signals of the feedback loop are: the volume of deformation and vibrations in the selected structures node.

Abstract: This paper presents approach for the damage growth monitoring and early damage detection in the PZL-130 ORLIK TC II turbo propeller military trainer based on the array of the PZT sensors which will be deployed in the structure of the aircraft. Special attention will be paid to the preliminary results of the statistical models which provide an automated tool to infer about the damage presence and its size. In particular the effectiveness of the selected signal characteristics will be assessed using dimensional reduction methods (PCA) and the so called averaged damage indices will be described. Verification of the several classification models based on the emerged damage indices will be presented using cross validation techniques. The preliminary results of the data collected from the subcomponents tests with the model description, as well as approach for the SHM system design will be delivered. The verification of the models results will be presented on the example of the aerospace structures.

Abstract: The effect of mode conversion of Lamb waves is a well known phenomenon. Lamb waves occur in multiple modes, which can transform into each other under special conditions. Typically mode conversion takes place at discrete positions inside a structure, e.g. damages and edges. However, we observed a continuous mode conversion in a multi-layer composite plate. The symmetric S0-mode converts continuously into the A0-mode without passing a macroscopic discontinuity. In the paper this phenomenon of continuous mode conversion is investigated experimentally as well as numerically.

Abstract: The paper presents the project of tank inspection robot. In order to discuss the designing process, algorithm of design has been provided. There are four design stages: the analysis of the construction problem, the synthesis, testing/improving robots construction and finally testing it. First stage of project process is divided into constructive and imitative analysis. Constructive analysis means searching for still not existing solutions of robots and detection methods. In this paper we concentrate only on constructive analysis.

Abstract: The first step of a methodological approach to the validation of the metal magnetic memory (MMM) method in non-destructive testing (NDT) applications and in systems used for the diagnosis of early stages of material fatigue in mechanical constructions (structural health monitoring, SHM, and prognosis health management, PHM) has been presented in the paper. The study is focused on the properties of the external natural source of magnetisation of the object under MMM examination and the impact of its components. The precise data of the Earth's geomagnetism measurements (from ground stations and satellites) and the revised model of the Earth's magnetism can be applied in order to calibrate high sensitive magnetic field sensors, validate measurement results and extend the functional capacity of the MMM method.