Universal damage indices in aircraft Structural Health Monitoring systems

Systemy monitorowania struktury (SHM) stanowią jedną z najintensywniej rozwijanych technologii, mających na celu zwiększenie bezpieczeństwa eksploatacji statków powietrznych. Wnioskowania o stanie diagnozowanej struktury dokonuje się zazwyczaj na podstawie tzw. wskaźników uszkodzeń otrzymanych z różnorodnych charakterystyk sygnału rejestrowanego przez sensory układu monitorującego. W niniejszej pracy zbadana zostanie efektywność wybranych wskaźników uszkodzeń w ocenie stanu konstrukcji używanych w lotnictwie przy pomocy systemu monitorowania wykorzystującego generację fal sprężystych. Zaproponowane zostaną również wskaźniki uszkodzeń o charakterze uniwersalnym, pozwalające wnioskować o stanie struktury w dużym stopniu niezależnie od jej typu i lokalizacji występujących uszkodzeń.Structural health monitoring (SHM) is an aircraft operation safety enhancing technology which nowadays undergoes rapid development. Structural health of a test structure is inferred from damage indices - various characteristics of the signal registered by transducers of the monitoring system. In this paper, we investigate the efficiency of selected damage indices in the evaluation of the health of structures used in aviation. We propose also damage indices having universal properties, useful in structural health assessment irrespectively of its type and the damage localization

Assessment of Sensor Technologies for Aircraft SHM Systems

SHM is a monitoring system which uses sensors, actuators and data transmission, acquisition and analysis, permanently integrated with the inspected object. The objective of SHM is to detect, localize, identify and predict development of fatigue fractures, increasing safety and reliability. This paper presents an assessment of sensor technologies used in aircraft SHM system. Due to the fact that most of these measurement methods are relatively new and still under development the present appraisal focuses on a number of parameters with reference to each method, including a sensor’s installation issues, reliability, power consumption, sensor infrastructure, sensitivity and cost and availability. The work is predominantly focused on the assessment of permanently bonded sensors, such as foil strain gages, Comparative Vacuum Monitoring (CVM), Piezo sensors (PZT), Eddy-Current Transducers (ECT). Finally, all these methods are briefly discussed

On the evaluation of a coupled sequential approach for rotorcraft landing simulation

Maximum loads acting on aircraft structures generally arise when the aircraft is undergoing some form of acceleration, such as during landing. Landing, especially when considering rotorcrafts, is thus crucial in determining the operational load spectrum, and accurate predictions on the actual health/load level of the rotorcraft structure cannot be achieved unless a database comprising the structural response in various landing conditions is available. An effective means to create a structural response database relies on the modeling and simulation of the items and phenomena of concern. The structural response to rotorcraft landing is an underrated topic in the open scientific literature, and tools for the landing event simulation are lacking. In the present work, a coupled sequential simulation strategy is proposed and experimentally verified. This approach divides the complex landing problem into two separate domains, namely a dynamic domain, which is ruled by a multibody model, and a structural domain, which relies on a finite element model (FEM). The dynamic analysis is performed first, calculating a set of intermediate parameters that are provided as input to the subsequent structural analysis. Two approaches are compared, using displacements and forces at specific airframe locations, respectively, as the link between the dynamic and structural domains

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

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

Assessment of Sensor Technologies for Aircraft SHM Systems

SHM is a monitoring system which uses sensors, actuators and data transmission, acquisition and analysis, permanently integrated with the inspected object. The objective of SHM is to detect, localize, identify and predict development of fatigue fractures, increasing safety and reliability. This paper presents an assessment of sensor technologies used in aircraft SHM system. Due to the fact that most of these measurement methods are relatively new and still under development the present appraisal focuses on a number of parameters with reference to each method, including a sensor’s installation issues, reliability, power consumption, sensor infrastructure, sensitivity and cost and availability. The work is predominantly focused on the assessment of permanently bonded sensors, such as foil strain gages, Comparative Vacuum Monitoring (CVM), Piezo sensors (PZT), Eddy-Current Transducers (ECT). Finally, all these methods are briefly discussed

Introduction of an Individual Aircraft Tracking Program for the Polish Su-22

The Su-22 fighter-bomber is a military aircraft used in the Polish Air Force (PLAF) since the mid 1980’s. By decision of the Ministry of National Defence Republic of Poland, the assumed service life for this type of aircraft was prolonged up to 3200 flight hours based on the Full Scale Fatigue Test (FSFT) results. The FSFT was conducted using the real load profile defined during the Operational Load Monitoring Program (OLM) and the 3200 hour service life was also based on this load profile. In order to assure safe operation of all the 18 Su-22 aircraft, the Individual Aircraft Tracking program was introduced. The program was based on the results of the FSFT as well as the analysis of the flight parameters recorded by the THETYS onboard flight recorder. In this paper, the authors present the methodology, assumed fatigue hypothesis and preliminary results of the IAT program for the Polish Su-22

Modelling and experimental testing of thick CFRP composites subjected to low velocity impacts

The present paper investigates a modelling approach of experimentally tested thick panels made of Carbon Fibre Reinforced Polymers (CFRP). The coupons were made of 24 unidirectional (UD) laminae with a layup [45/0/-45/90]3s. The specimens were subjected to low velocity impact using a drop tower system. Several sensors, including a load cell and strain gauge, were utilized both for analysing the behaviour of the material against the impact and for performing a validation of the numerical models. Three energy levels were adopted: 8J, 10J and 12J. Numerical models were implemented into the finite element (FE) software LS-DYNA. A linear - elastic constitutive law with an instantaneous failure material was selected for mimicking the intralaminar behaviour of the carbon fibre composite. Enhanced Chang - Chang was adopted as the onset-of-failure criterion. This criterion is able to capture damage in different directions and permits the consideration (or not) of the shear behaviour in the failure equations. The capability of the model to capture the correct interface failure process was particularly emphasized and therefore cohesive elements with a bilinear traction - separation law were chosen for the reproduction of delamination. Finally, the experimental - numerical results were compared using first and foremost the overall delamination area and the curves force - time, force - displacement and absorbed energy - time as well as the strain measures obtained by the sensors

Composite Aerospace Structure Monitoring with use of Integrated Sensors

One major challenge confronting the aerospace industry today is to develop a reliable and universal Structural Health Monitoring (SHM) system allowing for direct aircraft inspections and maintenance costs reduction. SHM based on guided Lamb waves is an approach capable of addressing this issue and satisfying all the associated requirements. This paper presents an approach to monitoring damage growth in composite aerospace structures and early damage detection. The main component of the system is a piezoelectric transducers (PZT) network integrated with composites. This work describes sensors’ integration with the structure. In particular, some issues concerning the mathematical algorithms giving information about damage from the impact damage presence and its growth are discussed

An Approach to Damage Detection in the Aircraft Structure with the Use of Integrated Sensors – The Symost Project

This paper presents an approach to damage growth monitoring and early damage detection in the structure of PZL – 130 ORLIK TC II turbo-prop military trainer aft using the statistical models elaborated by the Polish Air Force Institute of Technology (AFIT) and the network of the sensors attached to the structure. Drawing on the previous experiences of the AFIT and AGH in structural health monitoring, the present research will deploy an array of the PZT sensors in the structure of the PZL -130 Orlik TC II aircraft. The aircraft has just started Full Scale Fatigue Test (FSFT) that will continue up to 2013. The FSFT of the structure is necessary as a consequence of the structure modification and the change of the maintenance system - the transition to Condition Based Maintenance. In this paper, a novel approach to the monitoring of the aircraft hot-spots will be presented. Special attention will be paid to the preliminary results of the statistical models that provide an automated tool to infer about the presence of damage 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 delivered. Moreover, the results of the signal classification based on the neural network will be presented alongside the numerical model of the wave propagation. The work contains selected information about the project scope and the results achieved at the preliminary stage of the project