Sławomir Klimaszewski

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.

MODIFIED HAGG & SANKEY METHOD TO ESTIMATE THE BALLISTIC BEHAVIOUR OF LIGHTWEIGHT METAL/COMPOSITE/CERAMIC ARMOUR AND A FUSELAGE SKIN OF AN AIRCRAFT

Hagg & Sankey method assesses the functionality of containment rings, which prevent perforation of an aircrafts elements from turbine engine disc fragments after disc burst. However, the method assumption was based on studies of mechanism of destruction of ballistic shields made of among others ceramics, by small arms bullets. The hard ceramic facing of the ballistic shield blunts the projectile and breaks up the projectiles hard core used for armour piercing. As an impact result, a conoid of finely pulverized ceramic dust is formed, absorbing energy in the formation process. The dust, containing the remnants of the projectiles energy hits the backing, but is now spread over a larger area. With backings made of fibre, energy is absorbed in stretching, breaking and delamination. With backings made of ductile metal, energy is absorbed in elastic deformation. Modification of the method consisted of taking into account the stratification of the ceramic-metal composite and the occurrence of an aircraft stiffened skin, in order to better assess the effectiveness of ballistic shields. The concept of estimating the resistance was based on the described destruction mechanism, where the object of analysis is a metal containment ring with an additional ceramic protective ballistic shield. A comparison of two scenarios- with and without an additional 2 mm aluminum alloy skin was taken into account. For this particular scenario, results were sufficient for both of the two analyzed endurance criteria.

The Fatigue Life Assessment of PZL-130 Orlik Structures Based on Historical Usage Data

The Fatigue Life Assessment of PZL-130 Orlik Structures Based on Historical Usage Data Material fatigue is the basic factor limiting aircrafts durability. It comes from the fact that changing loads affect aircraft structure as well as from the fact that aircrafts mass restrictions do not allow for diminishing stress to the level when material fatigue does not occur. Estimating fatigue durability of a particular structure as well as its actual fatigue damage degree is possible when the history of loads affecting the structure is known. Accuracy of loads monitoring influences the accuracy of indicated fatigue wear. In case of older structures, which have been maintained according to safe life principle, the number of hours have been commonly used as a fatigue wear indicator. After aircraft structure reaches flying time estimated by the produces, it is considered as fatigue wear and it is no longer in service. In case of a lack of results of loads spectrum measurements, results of tests conducted for other aircraft (of similar structure and assignment) can be used. For this purpose, average loads spectrum has been elaborated for particular aircraft groups, for example, HELIX, FELIX, FALSTAFF, ENSTAFF, TWIST(10). In the case of small aircraft, the data from FAA (2) report have been often used. This article describes the way of fatigue wear estimation for PZL-130 Orlik aircraft on the basis of historical data from flight recorders.

Structural Load Monitoring Systems for Military Aircraft in the Polish Armed Forces with Examples of Selected Activities

Airplanes and helicopters currently operated by the Polish Armed Forces have been introduced into service without any load monitoring systems. The only exception is the F-16 and its Aircraft Structural Integrity Program.

Model Podejmowania Decyzji w Oparciu o Wartości Służący Ocenie Wariantów Systemu Monitorowania Stanu Technicznego Struktury Statków Powietrznych z Punktu Widzenia Wymagań Użytkownika Wojskowego

Streszczenie Niniejszy artykuł opisuje model podejmowania decyzji w oparciu o wartości (ang. Value-Focused Thinking - VFT) opracowany w celu oceny różnych wariantów wdrożenia systemu monitorowania stanu technicznego struktury (ang. Structural Health Monitoring - SHM) wojskowego statku powietrznego. Rozpatruje się cztery warianty wspomnianego systemu (SHM) oparte na: kontroli wzrokowej (aktualne podejście), czujnikach piezoelektrycznych (PZT), czujnikach światłowodowych z siatką Bragga (FBG) i czujnikach próżniowych (Comparative Vacuum Monitoring - CVM). Przedstawiono przykład numeryczny w celu zilustrowania możliwości modelu. Analizy wrażliwości są wykonane dla takich wartości jak koszt, wydajność, dostępność statku powietrznego oraz poziom gotowości technologicznej (Technology Readiness Level - TRL), aby zbadać wpływ tych parametrów na całkowitą wartość informacji z zakresu stanu technicznego struktury dostarczanych przez określony wariant systemu SHM.

Value-Focused Thinking Model to Evaluate SHM System Alternatives From Military end User Requirements Point of View

Abstract The article describes Value-Focused Thinking (VFT) model developed in order to evaluate various alternatives for implementation of Structural Health Monitoring (SHM) system on a military aircraft. Four SHM system alternatives are considered based on: visual inspection (current approach), piezoelectric (PZT) sensors, Fiber Bragg Grating (FBG) sensors and Comparative Vacuum Monitoring (CVM) sensors. A numerical example is shown to illustrate the model capability. Sensitivity analyses are performed on values such as Cost, Performance, Aircraft Availability and Technology Readiness Level in order to examine influence of these values on overall value of structural state of awareness provided by particular SHM system alternative.

Fatigue Cracks Detection using PZT Transducers under the Influence of Uncertain Environmental Factors

Abstract This paper presents technique for qualitative assessment of fatigue crack growth monitoring, utilizing guided elastic waves generated by the sparse PZT piezoelectric transducers network in the pitch – catch configuration. Two Damage Indices (DIs) correlated with the total energy received by a given sensor are used to detect fatigue cracks and monitor their growth. The indices proposed carry 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 alter over a long term, leading to the misclassification problem. Considering a single sensing path, it is very difficult to distinguish whether the resultant change of DIs is caused by a damage or due to decoherence of these DIs. Therefore, assessment approaches based on threshold levels fixed separately for DIs obtained on each of the sensing paths, would eventually lead to a false call. An alternative approach is to compare changes of DIs for all sensing paths. Developing damage distorts the signal only for the sensing paths in its proximity. In order to decrease the misclassification risk, a method of compensating such DIs drift is proposed. The main features and damage detection capabilities of this method will be demonstrated by conducting 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.

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

Combat survivability of helicopter/Analiza żywotności bojowej śmigłowca

Abstract The work provides a preliminary breakdown susceptibility analysis for a Mi-17 helicopter in combat conditions. An analysis of breakdown forms and consequences for helicopter sections and installations in battle conditions including probability of being shot down when hit was made. The article presents a theoretical outline for calculation methods on helicopter kill probability in case of being shot, depending on critical element configuration and number of hits. The probability figures have been calculated for a specific model describing a Mi-17 helicopter. As a result of the conducted analysis it was possible to determine, for a specified weapon caliber, probabilities and effects of receiving combat damage. These results can be used as a starting point for developing a new armed version of the helicopter. Streszczenie Celem pracy jest wstępna analiza podatności na uszkodzenia w warunkach bojowych śmigłowca Mi-17 dla wybranych scenariuszy oddziaływań bojowych. Została przedstawiona analiza postaci i skutków uszkodzeń zespołów i instalacji w warunkach bojowych z określeniem prawdopodobieństwa zestrzelenie śmigłowca pod warunkiem trafienia w niego. W niniejszej pracy przedstawiono zarys teoretyczny metod obliczania prawdopodobieństwa zestrzelenia statku powietrznego w zależności od konfiguracji elementów krytycznych oraz liczby postrzałów. Prawdopodobieństwa te zostały obliczone dla konkretnego modelu obrazującego śmigłowiec Mi-17. W wyniku przeprowadzonej analizy możliwe było, dla przyjętych środków rażenia, określenie ww. prawdopodobieństw i skutków uszkodzeń bojowych. Wyniki te mogą stanowić wyjściową bazę przy opracowywaniu nowej uzbrojonej wersji śmigłowca.

Zarys Probabilistycznej Metody Określenia Trwałości Zmęczeniowej Wybranych Elementów Konstrukcji Statku Powietrznego DLA Zachowania Wymaganego Poziomu Bezpieczeństwa Lotów

Zarys Probabilistycznej Metody Określenia Trwałości Zmęczeniowej Wybranych Elementów Konstrukcji Statku Powietrznego DLA Zachowania Wymaganego Poziomu Bezpieczeństwa Lotów W artykule przedstawiono zarys probabilistycznej metody wyznaczania trwałości zmęczeniowej elementu konstrukcji statku powietrznego dla przyjętego poziomu bezpieczeństwa lotów. W prezentowanej metodzie wykorzystane są: • eksploatacyjne widmo obciążenia elementu konstrukcyjnego statku powietrznego, • zależność Parisa określająca prędkość propagacji pęknięcia zmęczeniowego w ujęciu deterministycznym, • równanie różnicowe do charakterystyki narastania pęknięcia w ujęciu probabilistycznym, • funkcja gęstości narastania długości pęknięcia elementu w postaci rozwiązania równania Fokkera-Plancka. Otrzymane wyniki pozwoliły na wyznaczenie postaci funkcji gęstości czasu (nalotu) niezbędnego do przekroczenia dopuszczalnej długości pęknięcia. Mając wyznaczoną tę funkcję, określono niezawodność elementu, którą następnie wykorzystano do wyznaczenia trwałości zmęczeniowej elementu konstrukcji. Rozpatrzono dwa przypadki rozwiązania, zależne od współczynnika m występującego we wzorze Parisa, tzn. dla m = 2 i m ≠ 2.