Papers by Author: Tadeusz Uhl

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Authors: Wieslaw Jerzy Staszewski, Ruztamreen bin Jenal, Andrzej Klepka, Mariusz Szwedo, Tadeusz Uhl
Abstract: Non-contact optical/laser measuring techniques are very attractive in many engineering applications. The paper demonstrates examples related to structural health monitoring. Various methods based on strain, vibration and ultrasound measurements are presented together with relevant references. Applications examples utilise in-plane and out-of-plane measurements taken by 1-D and 3-D laser Doppler vibrometers.
Authors: Łukasz Pieczonka, Andrzej Klepka, Wieslaw Jerzy Staszewski, Tadeusz Uhl, Francesco Aymerich
Abstract: The paper investigates experimentally the effect of low-frequency vibration on nonlinear vibro-acoustic wave modulations applied to the detection of Barely Visible Impact Damage (BVID) in a composite plate. Finite Element (FE) modeling was used in a pretest stage to identify different motion scenarios of delaminated surfaces and relate them to natural frequencies of the damaged plate. In particular the opening-closing and frictional sliding actions of the defected interfaces have been considered. Subsequently, the identified frequencies have been used for low frequency excitation in nonlinear acoustic experiments on a composite plate with impact damage.
Authors: Ziemowit Dworakowski, Łukasz Ambroziński, Pawel Packo, Krzysztof Dragan, Tadeusz Stepinski, Tadeusz Uhl
Abstract: Lamb waves (LW) are used for damage detection and health monitoring due to the long range propagation ability and sensitivity to structural integrity changes as well as their robustness in different applications. However, due to the dispersive character and multimode nature of LWs, analysis of the acquired ultrasonic signals is very complex. It becomes even more difficult when applied to a complex structure, for instance, an aircraft component with riveted joints and stringers characterized by difficult geometries. Therefore, numerous approaches to the evaluation of damage indices have been proposed in the literature. In this paper, comparison a number of damage indices applied to LWs testing in aircraft aluminum panels. The damage indices, known from the literature have been selected from the application point of view. Artificial neural network has been used for the classification of fatigue cracks and artificial damages induced in the specimens taken from a real aircraft structure. Article presents results of simulation, data analysis and data classification obtained using selected and dedicated neural network. The main aim of the presented research was to develop signal processing and signal classification methods for an aircraft health monitoring system. The article presents a part of the research carried out in the project named SYMOST.
Authors: Piotr Kohut, Krzysztof Holak, Tadeusz Uhl, Jędrzej Mączak, Przemysław Szulim
Abstract: Structural Health Monitoring (SHM) is an emerging field of technology that involves the integration of sensors, data transmission, processing and analysis for detection, as well as localization and assessment of damage which can lead to its failure in the future [1,. In general, SHM methods can be divided into two groups: local and global ones. The second group can be applied if a global change in the geometry of a structure can be observed. In practice, the most commonly used methods of damage detection are based on the analysis of variations in various dynamic properties caused by damage [3,. However, the excitation of large structures can be costly and difficult. The acquisition of static deflection requires much less effort, which makes the damage detection methods based on changes in deflection curves more attractive for practical use [5-1. Damage detection and localization methods require a densely sampled deflection curve.
Authors: Krzysztof Mendrok, Jarosław Bednarz, Tadeusz Uhl
Abstract: 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.
Authors: Krzysztof Mendrok, Tadeusz Uhl
Abstract: Ritz vectors are parameters, which describe object dynamics in similar way as modal vectors. Their advantage with respect to modal vectors is a fact, that less number of them is required to estimate object response. It is also proofed, that Ritz vectors are more sensitive for damage detection then modal vectors. The problem which arises, when one wants to use Ritz vectors for damage assessment is that there are no many methods to extract Ritz vectors from operational data. In addition, the methods require knowledge of analytical mass matrix or state a space model matrix, which makes them rather complicated. In the paper two Ritz vectors extraction methods are taken into account. First bases on flexibility matrix and second is related with state space model. Both of them are evaluated with respect to analytical procedure of Ritz vectors calculation. For the vectors evaluation, a simulation data from theoretical model were used. In next step Ritz vectors were extracted from data measured on a real structure. On the structure damage was simulated. The Ritz vectors extracted with use of both tested methods were used to detect damage.
Authors: Lukasz Ambrozinski, Tadeusz Stepinski, Tadeusz Uhl, Janusz Ochonski, Andrzej Klepka
Abstract: Guided waves (GW) based methods are a promising tool for structural health monitoring (SHM) of plate-like metallic and composite structures in which high safety standards are required. In this paper we present research with the aim to design and manufacture a prototype of Lamb waves (LW) SHM system. Two approaches can be applied for SHM of plate-like structures. One of them can be based on a sparse array and damage imaging involving incoherent summation of signals envelope. The second approach involves phased arrays with transducers spaced at a distance lower than half wavelength of the excited Lamb-mode. The influence of an arrays parameters on beamforming of Lamb waves is discussed in the case of linear array. It appears that an unequivocal localization of damage on a plate requires a 2D arrays topology; therefore a star-shaped active array was designed and manufactured for the developed SHM system. Two signal processing approaches were applied for that array, the standard one, based on the delay and sum (DAS) synthetic aperture focusing scheme, and the second one, using a self-focusing technique to obtain the separate images for each scatterer existing in the plate.
Authors: Krzysztof Grabowski, Paulina Zbyrad, Tadeusz Uhl
Abstract: In this paper there wasdevelopeda CNT based sensor applied to the tested material and integrated with it. MWCNTs weremixed with polymer and then applied to the materials (fiber glass composites) with the use of screen printing. The surface and the inner part of the sensing material were investigated using SEM. The most importantand noticeable thing was dispersion of CNTs in epoxy.Moreover, the sensors were tested under the different loads. There were three runs for the same compositions of CNT/epoxy. Results from the test runs were compared to the images from SEM and discussed. Screen printing technique has shown promising results for the application and integration of the sensors on the base materials leading to the conclusion to do more research for the screen printing technique for application of CNT/epoxy sensors for large area appliaction and variant environments.
Authors: Michał Mańka, Adam Martowicz, Mateusz Rosiek, Tadeusz Uhl
Abstract: During recent years structural health monitoring (SHM) systems have gained growing attention. Widely applied methods in SHM are methods based on the ultrasonic Lamb waves (LWs) which are also known as plate waves. LWs may be generated and sensed using different types of transducers and their selection is essential for the SHM systems performance. Among transducers used for generation and sensing of such waves, Interdigital Transducers (IDTs) are ones of the most promising types. Their main advantages are: mode selectivity, high excitation strength, wave directivity, small sizes and relatively low cost. In most cases IDTs are made of piezoceramics or piezoelectric polymers what makes them stiff and fragile. Contrary to the piezoceramic transducers, the ones based on piezocomposites (i.e.: macro-fiber composite) are flexible with the comparable efficiency of piezoelectric effects. The MFC transducers are usually optimized as actuators and they are not designed to any specific frequency. It appears, however, that sparse comb-like electrodes used in interdigital transducers create very interesting properties of mode selectivity. In the paper, after the introduction and short discussion about advantages and disadvantages of the IDTs, a novel type of the interdigital transducer, based on elastic macro-fiber composite, is presented. Next, the results of the numerical and experimental tests of the MFC based IDT designed for the A0 mode excitation in a 4mm-thick aluminium plate is presented. In the final part of the paper advantages and disadvantages of the investigated transducer are discussed.
Authors: Mateusz Rosiek, Adam Martowicz, Tadeusz Uhl
Abstract: This paper concerns an approach based on the electromechanical impedance for damage detection and monitoring of aircraft components. In the introductory part of the paper the theory of proposed method and the characteristics of elaborated structural health monitoring system are briefly described. Afterwards, applications of described system applied to damage detection in different aircraft components are presented. First, the process of monitoring of bolted joints localized in the fuselage is described and effectiveness of this process is discussed. In the application four PZT patches were used to track a torque decrease in three joints. The latter application deals with monitoring of riveted engine housing made of aluminium. Introduced notch was monitored with two MFC transducers. In both mentioned cases the frequency characteristics of measured impedance were compared using different deterministic and statistical damage indexes.
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