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Major airframe fatigue test (MAFT) setup of a fighter airplane. 

Major airframe fatigue test (MAFT) setup of a fighter airplane. 

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An overview of the aircraft design and maintenance process is given with specific emphasis on the fatigue design as well as the phenomenon of the ageing aircraft observed over the life cycle. The different measures taken to guarantee structural integrity along the maintenance process are addressed. The impact of structural health monitoring as a me...

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... a major airframe (full scale) fatigue test (MAFT; figure 4). The airframe structure is mounted on a test rig and is loaded repeatedly by different loading cylinders according to the loading combinations and sequences for the duration of the aircraft’s qualified life times the security factor, which in the case of the example shown in figure 3 would be 6000 flight hours ! 3 Z 18 000 flight hours . The aircraft structure is inspected regularly and any cracks or damage monitored is fed back for redesign of the aircraft structure or amendments to the maintenance procedures. A chronology of the aircraft structure fatigue verification process is given in figure 5. It shows that loads and fatigue assessment are the result of an iterative process and thus appear several times. It further shows that MAFT is not even finished when the first flight is done and may even not be finished when the first aircraft enters into service with the customer. Since the operational life of military aircraft has increased significantly over the past years with 50 years due to become standard and up to 100 years to be discussed for specific cases (e.g. the B-52 bombers) a fatigue assessment becomes appropriate once the aircraft type is close to reaching its mid-operational life. This is mainly required because operational loads resulting from aircraft modifications, change in payloads, flight envelops or flight environment may have significantly changed over that first period of the operational life and may have implications on the aircraft’s remaining operational life. In some of the cases, an aircraft structure taken out of service is therefore reassessed in a so-called mid-life update MAFT. ( a ) Inspection sequences Aircraft, civil as well as military, are inspected according to well-prescribed procedures. It starts with a pre- and post-flight visual inspection of the aircraft and ends up in a full dismantling or at least disassembly of major components such that fatigue, corrosion or wear can be determined at any of the ...

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... For the elements designed with DT philosophies, the structures need to be designed with the configurations of slow crack growth, or fail-safe supported by crack arrests or multiple load paths. Fig. 2 is such kind of design flowchart illustrated by C. Boller in Ref. [12]. It has also been discussed by S.M.O. ...
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This article started with a review on the evolutionary history of airworthiness regulations. Requirements for Durability and Damage Tolerance designs in current airworthiness regulations are an accumulation result of lessons learnt from various aircraft accidents. “Analysis, supported by tests” can be concluded as the baseline of the airworthiness regulations. Although the research works for the fatigue failures in metallic structures have been continued for more than 170 years, unforeseen fatigue failures are still occurring in the full-scale fatigue validation tests and aircraft operations. Various influence factors to the uncertainties of fatigue failures have been discussed from the aspects of metallic materials, structure features, machining processes and assembly processes. It can be concluded that considering the effects of manufacturing processes on the fatigue failure, generating the design values and validating related design methods/tools with test pyramids are the best way to design, produce, operate and maintain aircraft with lightweight structures.
... Sensor integrity module. methods such as the Palmgren-Miner damage law [186]. This method quantifies the cumulative fatigue damage through a damage index (DI) calculated by: ...
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Integrated System Health Management (ISHM) is a promising technology that fuses sensor data and historical state-of-health information of components and subsystems to provide actionable information and enable intelligent decision-making regarding the operation and maintenance of aerospace systems. ISHM fundamentally relies on assessments and predictions of system health, including the early detection of failures and estimation of Remaining Useful Life (RUL). Model-based, data-driven or hybrid reasoning techniques can be utilized to maximise the timeliness and reliability of diagnosis and prognosis information. The benefits of ISHM include enhancing the maintainability, reliability, safety and performance of systems. The next evolution of the ISHM concept, Intelligent Health and Mission Management (IHMM), delves deeper into the utilization of on-line system health predictions to modify mission profiles to ensure safety and reliability, as well as efficiency through predictive integrity. This concept is particularly important for Trusted Autonomous System (TAS) applications, where an accurate assessment of the current and future system state-of-health to make operational decisions (with or without human intervention) is integral to both flight safety and mission success. IHMM systems introduce the capability of predicting degradation in the functional performance of subsystems, with sufficient time to dynamically identify which appropriate restorative or reconfiguration actions to take in order to ensure that the system can perform at an acceptable level of operational capability before the onset of a failure event. This paper reviews some of the key advancements and contributions to knowledge in the field of ISHM for the aerospace industry, with a particular focus on various architectures and reasoning strategies involving the use of artificial intelligence. The paper also discusses the key challenges faced in the development and deployment of ISHM systems in the aerospace industry and highlights the safety-critical role that IHMM will play in future cyber-physical and autonomous system applications (both vehicle and ground support systems), such as Unmanned Aircraft Systems (UAS) Traffic Management (UTM), Urban Air Mobility (UAM) and Distributed Satellite Systems (DSS).
... In general, any monitoring system entails the observation of a structure over time using periodical measurements, the extraction of proper features from these measurements and the analysis and interpretation of these features to determine the current state of the system, whether the focus is on its health state or its load level [6,7]. The actual state of the investigated system can often result from a statistical comparison of the current data with a database of experimental data. ...
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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.
... In aircraft SHM system appear in landing gear monitoring, engines and composite structures. While most of the aircraft structures other than composite structures are made from ductile alloys that can endure crack growth over time, brittle alloys have high strength these differences will effect the SHM [15]. The Nanotechnology plays a vital role in SHM where the material itself act as the sensor so thatit will not degrade the mechanical property of aircraft structures. ...
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Nowadays, GFRP, i.e., glass fiber reinforced polymer composites, are widely used in manufacturing process especially in aircraft industries and automobiles due to their beneficial mechanical and thermal properties such as specific strength and better resistance to corrosion. In this present research, the electrostatic-bonded PVDF-MWCNT fiber composition and GFRP had been used for structural health monitoring (SHM) of composite material. PVDF-MWCNT had been embedded to upper-most layer of the nonconductive materials which is GFRP, i.e., glass fiber reinforced polymers for the undertaking process. This research takes place mainly to improve the multifunction ability. Mainly, the manufacture specimen was characterized into two types; they are mechanical load characterization and material characterization. It is the first time this fiber composition is used in composite materials for monitoring purposes. MWCNT fiber easily penetrates and does not decrease the mechanical properties of material. In this investigation, SEM, i.e., scanning electron microscope and XRD (X-ray diffraction) were used for material characterization process to determine the dispersion of MWCNT with polymer, crystalline structure. The manufactured specimen another characterization namely mechanical load characterization it had done in two ways are incremental–decremental tensile loading and three-point loading testing in order to determine the sensitivity of the material during loading and unloading, material damage identification. The MWCNT fiber worked as a sensor in both tensile and compression loadings. So we mainly used the MWCNT for this process.
... The composite structure serving process is vulnerable to many factors that may cause internal damage, such as hail impact, birds, and lightning effects. Sometimes damage cannot be detected in the early stages of production or in a timely manner and this can cause damage accumulation, which can further result in a significant decrease in structural strength and stability, and the safety of the aircraft structure could be seriously affected and its service life also be significantly shortened [1][2][3]. Therefore, it is of great significance to monitor structural health and identify damage in an aviation composite structure in a timely manner, and this requires the application of a structural health monitoring method. ...
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As one of the active structural health monitoring methods based on the Lamb wave, the ultrasonic phased-array damage detection method can provide information such as damage location and range more intuitively, which is why this method is a research hotspot in the field of Lamb wave-based damage monitoring. However, the ultrasonic phased-array damage detection method intended for the far field is not applicable to near-field damage monitoring. In addition, the traditional one-dimensional piezoelectric phased-array damage imaging method suffers from a blind area in the near field, and the data collection time of its angle scanning is relatively long. In view of these problems, this paper proposes an omnidirectional damage imaging monitoring method, combining the near-field sampling phased-array damage monitoring algorithm and the two-dimensional phased-array. The proposed method is verified by experiments using complex composite materials, and the results obtained show that the proposed omnidirectional near-field sampling phased-array damage imaging method is suitable for real-time damage detection in complex composite materials.
... Stresses exceeding the elastic regime are not considered in our approach, as their occurrence might expose the vehicle to non-fatigue related failure modes and, based on the current standards, void the airworthiness of the aircraft altogether. Subsequently the cumulative fatigue is estimated based on the total cycle count using established methods such as the Palmgren-Miner damage law (Dowling 1988;Boller and Buderath 2007;Federal Aviation Authority 2005;Marczi 2004), crack growth (Molent et al. 2008;Zhuang et al. 2007) or probabilistic methods (Molent and Aktepe 2000;Ocampo et al. 2010;Xiang and Liu 2011). Th e Palmgren-Miner damage law is a linear fatigue damage theory that estimates cumulative fatigue damage at critical locations. ...
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This article proposes a novel and effective solution for estimating fatigue life of General Aviation (GA) airframes using flight data produced by digital avionics systems, which are being installed or retrofitted into a growing number of GA aircraft. In the proposed implementation, a flight dynamics model is adopted to process the recorded flight data and to determine the dynamic loadings experienced by the aircraft. The equivalent loading cycles at fatigue-critical points of the primary structure are counted by means of statistical methods. For validation purposes, the developed approach is applied to flight data recorded by a fleet of Cessna 172S aircraft fitted with a Garmin G1000 integrated navigation and guidance system. Based on the initial experimental results and the developed uncertainty analysis, the proposed approach provides acceptable estimates of the residual fatigue life of the aircraft, thereby allowing a cost-effective and streamlined structural integrity monitoring solution. Future developments will address the possible adoption of the proposed method for unmanned aircraft structural health monitoring, also considering the accuracy enhancements achievable with advanced navigation and guidance architectures based on Global Navigation Satellite Systems (GNSS), Vision-Based Navigation (VBN) Sensors, Inertial Measurement Units (IMU) and Aircraft Dynamics Model (ADM) augmentation.
... 3 The existing literature on it is extensive 2,4,5 and plenty of methods have thus far been developed for operational data collection and fatigue life management. [6][7][8][9][10] Generally realistic load history can be accurately monitored using flight parameter-based method or strain gauges at critical points, complemented by fatigue test calibration and data processing. 11,12 Pertinent approaches regarding fatigue damage analysis fall into two categories: fatigue analysis-based method and crack growth analysis-based method; 13 however, there are limitations in application of both methods. ...
Article
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Individual aircraft life monitoring is required to ensure safety and economy of aircraft structure, and fatigue damage evaluation based on collected operational data of aircraft is an integral part of it. To improve the accuracy and facilitate the application, this paper proposes an engineering approach to evaluate fatigue damage and predict fatigue life for critical structures in fatigue monitoring. In this approach, traditional nominal stress method is applied to back calculate the S-N curve parameters of the realistic structure details based on full-scale fatigue test data. Then the S-N curve and Miner’s rule are adopted in damage estimation and fatigue life analysis for critical locations under individual load spectra. The relationship between relative small crack length and fatigue life can also be predicted with this approach. Specimens of 7B04-T74 aluminum alloy and TA15M titanium alloy are fatigue tested under two types of load spectra, and there is a good agreement between the experimental results and analysis results. Furthermore, the issue concerning scatter factor in individual aircraft damage estimation is also discussed.
... Operation of the structure health monitoring systems involves the installation of different types of sensors on the structures to determine the effects of physical (humidity and ambient temperature) and power (static, cyclic, impact and other types of loads) actions on their strength and durability [1, [4][5]. ...
Chapter
This chapter provides an overview of the most relevant methods for monitoring the integrity of structures made of isotropic (metals and alloys) and anisotropic (polymer composite) materials, which are widely used in the manufacture of parts and construction structures in the modern industry. Special attention is paid to ensuring the safe operation of aircraft structures, the use of onboard monitoring systems which will allow to reduce economic costs in the near future and to increase flying safety. The paper describes different variants of implementation of the onboard recording systems of data in the analysis of the actual state of the elements of the air frame. The advantages are shown, due to which the construction monitoring will be able to replace the existing system of provision and supporting of the airworthiness, implemented through periodic inspections.
... This may be either achieved such that a crack grow at any time up to a certain where it then be stopped by a crack stopper or the component will have fractured and the loads transferred by that component will be transferred by some other component. Damage tolerance can however also be based on assuming a crack to be available at a badly inspect able location and to determine how much the crack is allowed to grow until it finally reaches a critical stage [8]. ...
... Despite a number of studies on Lamb wave damage detection have been reported in existing studies, there are still some challenges for engineering applications [16,17]. First, a great number of experimental datasets of Lamb wave testing are required to establish a reliable and accurate crack size quantification model. ...
Article
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This paper presents a systematic and general method for Lamb wave-based crack size quantification using finite element simulations and Bayesian updating. The method consists of construction of a baseline quantification model using finite element simulation data and Bayesian updating with limited Lamb wave data from target structure. The baseline model correlates two proposed damage sensitive features, namely the normalized amplitude and phase change, with the crack length through a response surface model. The two damage sensitive features are extracted from the first received S0 mode wave package. The model parameters of the baseline model are estimated using finite element simulation data. To account for uncertainties from numerical modeling, geometry, material and manufacturing between the baseline model and the target model, Bayesian method is employed to update the baseline model with a few measurements acquired from the actual target structure. A rigorous validation is made using in-situ fatigue testing and Lamb wave data from coupon specimens and realistic lap-joint components. The effectiveness and accuracy of the proposed method is demonstrated under different loading and damage conditions.