Artur Kurnyta

Damage Size Estimation of the Aircraft Structure with Use of Embedded Sensor Network Generating Elastic Waves

One of the approach to develop a system of continues, automated monitoring of the health of the structures is to use elastic waves excited in a given medium by piezoelectric transducers network. Elastic waves depending on their source and the geometry of the structure under consideration can propagate over significant distance. They are also sensitive to local structure discontinuities and deformations providing a tool to detect local damage of large aerospace structures. In the paper the issue of fatigue crack growth monitoring by means of elastic guided waves actuated by a sparse array of sensors will be presented. In particular we propose signal characteristics, robust enough to detect different kinds of damages: Barely Visible Impact Damages (BVIDs) in composite materials and fatigue cracks of metallic structures. The model description and the results of specimen tests verifying damage detection capabilities of the proposed signal characteristics are delivered in the paper. Some issues concerning the proposed damage indices and its application to damage detection and its monitoring are also discussed.

Energy Correlated Damage Indices in Fatigue Crack Extent Quantification

Signals received by piezoelectric transducers (PZT) network can be influenced by many factors. Apart from environmental conditions, whose variability should be compensated, significant difference in a signal can be also caused by relative geometry changes of a designed sensors node, e.g. the damage localization and its orientation with respect to sensors location in the node. In the adopted approach a set of damage indices (DIs), carrying marginal signal information content and correlated with the total energy received by a given sensor are proposed. These are sensitive to the two main modes of guided wave interaction with a fatigue crack, i.e. its transmission and reflection from a damage. Detailed description of DIs detection capabilities are delivered in the paper. Two dimensional reduction techniques: Principal Component Analysis and Fishers Linear Discriminant are compared. The results of the data collected from specimen fatigue test are used to compare several classification models based on the emerged effective damage indices.

Structural Health Monitoring of a Composite Panel Based on PZT Sensors and a Transfer Impedance Framework

One of the ideas for development of Structural Health Monitoring (SHM) systems is based on excitation of elastic waves by a network of PZT piezoelectric transducers integrated with the structure. In the paper, a variant of the so-called Transfer Impedance (TI) approach to SHM is followed. Signal characteristics, called the Damage Indices (DIs), were proposed for data presentation and analysis. The idea underlying the definition of DIs was to maintain most of the information carried by the voltage induced on PZT sensors by elastic waves. In particular, the DIs proposed in the paper should be sensitive to all types of damage which can influence the amplitude or the phase of the voltage induced on the sensor. Properties of the proposed DIs were investigated experimentally using a GFRP composite panel equipped with PZT networks attached to its surface and embedded into its internal structure. Repeatability and stability of DI indications under controlled conditions were verified in tests. Also, some performance indicators for surface-attached and structure-embedded sensors were obtained. The DIs’ behavior was dependent mostly on the presence of a simulated damage in the structure. Anisotropy of mechanical properties of the specimen, geometrical properties of PZT network as well as, to some extent, the technology of sensor integration with the structure were irrelevant for damage indication. This property enables the method to be used for damage detection and classification.

Transfer Impedance Approach to Damage Detection and Localization Based on RAPID Imaging Algorithm

One of the ideas for structural health monitoring (SHM) systems built is based on analysis of small displacements propagation excited in the element by a network of PZT piezoelectric actuators. Structural damages can result in observable changes of the signal generated by the network sensors, due to elastic wave interaction with damage. The electromechanical impedance (EMI) method approach to SHM, harmonic excitation of PZT is used, thus steady elastic waves are excited in the structure. The signal can be gather in the pulse – echo scheme, i.e. when single transducer is used both as a actuator and the receiver of waves, as well in the pitch – catch scheme, when a pair of transducers, the generator and the sensor, are used. For the latter EMI approach, the term Transfer Impedance Approach is sometimes used. In the paper, an approach for damage detection and localization with use of network of PZT sensors excited with harmonic signals in broad frequency spectrum is presented. In particular, some signal characteristics – called Damage Indices (DI’s) used for structure assessment are proposed and their properties are discussed. The DI’s have the property to assess the location a damage with respect to a single sensing path, formed by a pair of transducers, i.e. the generator and the receiver. Finally, the RAPID algorithm for damage localization with use of the information from all of the network sensing paths is applied.

Fatigue Cracks Detection and Their Growth Monitoring During Fatigue Test of a Helicopter Tail Boom

In the paper a technique for qualitative assessment of fatigue crack growth monitoring is presented, utilizing guided elastic waves generated by sparse PZT piezoelectric transducers network in the pitch – catch configuration. Two Damage Indices (DI’s) correlated with the total energy received by a given sensor are used to detect fatigue cracks and monitor their growth. The indices proposed carries marginal signal information content in order to decrease their sensitivity with respect to other undesired non-controllable factors which may distort the received signal. The reason for that is to limit the false calls ratio which besides the damage detection capability of a system, plays a crucial role in applications. However even such simplified damage indices can be altered over a long term, leading to the misclassification problem. Considering single sensing path, it is very difficult to distinguish whether the resultant change of DI’s is caused by a damage or due to such DI’s decoherence. Therefore assessment approaches based on threshold levels fixed separately for DI’s obtained on each of the sensing paths, would eventually lead to a false call. An alternative approach is to compare changes of DI’s for all of the sensing paths. A developing damage distort the signal only for sensing paths in its proximity. In order to decrease the misclassification risk a method to compensate such DI’s drift is proposed. The main features and damage detection capabilities of the method will be illustrated on a laboratory fatigue test of an aircraft panel. The proposed approach has been verified on a real structure during fatigue test of a helicopter tail boom. doi: 10.12783/SHM2015/11

Composite Diagnostics with Use of Embedded PZT Transducers—A Smart Structure Example

Application of guided waves excited by a network of PZT transducers integrated with a given structure is one of the promising approaches to Structural Health Monitoring (SHM). The performance of a SHM system based on PZT network is rooted in two distinct areas of the technology development, that is: the hardware and the signal analysis. The first includes is the type of transducers used to built a network and the way of their integration with a monitored structure. For composites, beside the possibility of the transducers attachment to a surface of an element, also immersing of PZTs into their internal structure is available. In the article Barely Visible Impact Damage (BVID) detection capabilities of the embedded and surface attached PZT transducers are compared in broad frequency range of the excitation. The damage detection capabilities are compared in the range 100 – 350 kHz. In addition to purely qualitative detection of damages a new algorithm of their localization is proposed and compared between the embedded and surface attached transducers for the frequency optimal to detect BVIDs. This algorithm is a modified version of the RAPID imaging method, but suitable to be used also in the case of non-homogeneous sensor networks. Finally the performance of a system is verified with use of a composite panel having PZT transducers embedded into its internal structure. The network geometry was tailored to fulfill specific demands regarding the structural performance. doi: 10.12783/SHM2015/72

Health Monitoring of the Aircraft Structure during a Full Scale Fatigue Test with Use of an Active Piezoelectric Sensor Network

The paper presents an approach to develop a system for fatigue crack growth monitoring and early damage detection in the PZL – 130 ORLIK TC II turbo-prop military trainer aircraft structure. The system functioning is based on elastic waves propagation excited in the structure by piezoelectric PZT transducers. In the paper, a built block approach for the system design, signal processing as well as damage detection is presented. Description of damage detection capabilities are delivered in the paper and some issues concerning the proposed signal processing methods and their application to crack growth estimation models are discussed. Selected preliminary results obtained during the Full Scale Fatigue Test thus far are also presented.

Health Monitoring of the Aircraft Structure during a Full Scale Fatigue Test with Use of Resistive Ladder Sensors

The paper presents an application of resistive ladder sensors (or resistive crack gages) for health monitoring of an aircraft structure. An experiment was conducted during a Full Scale Fatigue Test (FSFT) of PZL 130 ORLIK TC II turbo-prop military trainer. The sensor can be successively used to detect and quantify fatigue cracks. It is a parametric transducer, similar to foil strain gages. Differences in shape of the measuring grid can be noticed. Principle of operation, sensor’s characteristics as well as block diagram of measurement system is presented in the paper. Also examples, both laboratory and FSFT data are delivered to prove surface crack detection capabilities. Simultaneously with new data collection, some investigation is carried out, connected with customize hardware elaboration, signal processing and structure-sensor integration method, what is briefly described.

Analiza Metody Sterowania Predykcyjnego Dla Aktywnego Zawieszenia Magnetycznego

Abstract Syntezę regulatorów klasycznych przeprowadza się na podstawie znajomości parametrów modelu obiektu regulacji. Jednak wyznaczenie tych parametrów nie zawsze jest możliwe lub jest niezwykle trudne, zwłaszcza gdy zmieniają się one w trakcie okresu eksploatacji. W takim przypadku wykorzystuje się bardziej złożone metody sterowania, np. metodę sterowania predykcyjnego. W artykule przedstawiona została metoda sterowania predykcyjnego w układzie regulacji aktywnego zawieszenia magnetycznego, model matematyczny i symulacyjny takiego układu sterowania oraz wyniki wstępnych badań symulacyjnych analizowanego układu sterowania.

Analysis Of The Method Of Predictive Control Applicable To Active Magnetic Suspension Systems Of Aircraft Engines

Abstract Conventional controllers are usually synthesized on the basis of already known parameters associated with the model developed for the object to be controlled. However, sometimes it proves extremely difficult or even infeasible to find out these parameters, in particular when they subject to changes during the exploitation lifetime. If so, much more sophisticated control methods have to be applied, e.g. the method of predictive control. Thus, the paper deals with application of the predictive control approach to follow-up tracking of an active magnetic suspension where the mathematical and simulation models for such a control system are disclosed with preliminary results from simulation investigations of the control system in question.