Abstract: Blade vibrations in aircraft engines are a significant challenge that must be overcome during the design and development of modern turbine engines. Vibrations lead to cyclic displacements and result in alternating stress and strain in undesired environments (high temperatures, erosion, corrosion of the surface, etc.). Under resonance conditions, stress amplitudes can increase and exceed their safety limits, and in extreme cases, can lead to engine failure. One method to reduce resonance vibrations is to increase damping in the turbine assembly. This paper presents and describes vibration damping sources in the turbine, including aerodynamic, material, and friction damping. Additionally, typical damping values for each damping component are presented and compared. PubDate: Mon, 05 Jun 2023 00:00:00 GMT
Abstract: This work is focused on the checking of the correctness of the brazing process of honeycomb seals to stationary elements of aircraft turbine engines. It describes this process, paying attention to the aspects that have a fundamental impact on whether the seal will be brazed to the base as required, or whether unacceptable areas of non-brazing will appear. The aim of the study was to check the possibility of using the ultrasonic method to check the correctness of the brazing process of honeycomb seals and to compare the tests carried out using this method with the mostly used visual tests. The research carried out as part of the work showed very well that there are reasons to use the ultrasonic defectoscopy method to test the correctness of the brazing process of honeycomb seals in the elements of aircraft engines. This method also makes it possible to automate the checking process, fully document it and objectively assess the correctness of the connection. The results obtained in the study provide a very good starting point for further research, the aim of which will be to implement the ultrasonic defectoscopy method for testing the correctness of brazing honeycomb seals into practice in industrial conditions. PubDate: Thu, 20 Apr 2023 00:00:00 GMT
Abstract: In the present study it has been endeavored to estimate the fatigue crack propagation in V-notch Charpy specimens of 2024 T351 Al-alloy. For this purpose, a new application of fatigue crack growth (FCG) is developed based on the “Gamma function.” Experimental fatigue tests are conducted for stress ratios from 0.1 to 0.5 under constant amplitude loading. The empiric model depends principally on physical parameters and materials’ properties in non-dimensional form. Deviation percentage, prediction ratio, and band error are used for validation of the performance of the fatigue life. The results determined from Gamma application are in good agreement with experimental FCG rates and those obtained from using Paris law. PubDate: Thu, 20 Apr 2023 00:00:00 GMT
Abstract: In this work, cast steel G17CrMoV5-10 was investigated. The material subject to investigation as part of this study is commonly used to manufacture steam turbine casings. Modern steam turbines operate under elevated temperature and complex oscillated loads. Thus, the focus of this study was to investigate material under behavior during low cycle fatigue (LCF) test performance at 500°C with and without hold time in tension. During all types of test, cyclic softening of cast steel was noticed. Increasing of total strain rate and applying hold time significantly reduce fatigue life. During hold time, due to temperature and tension the material creep what is confirmed by increasing inelastic stain accommodation. PubDate: Mon, 13 Feb 2023 00:00:00 GMT
Abstract: The study investigates the sensitivity of numerical crack propagation estimations based on the Nasgro equation. The equation is widely used for crack propagation calculations since it considers the whole range of crack propagation speed from threshold to critical values of stress intensity factor range (∆K). The presented investigation is based on the actual results of the full scale fatigue test (FSFT) of the PZL-130 ‘Orlik’ TC-II aircraft. We provide a brief description of the test and the general approach followed in crack propagation estimations originally carried out after the test. The obtained results are verified in terms of variation of the input data. Overall results are compared and discussed. PubDate: Mon, 13 Feb 2023 00:00:00 GMT
Abstract: Fibre metal laminates (FMLs) consisting of layers made of PA6 polyamide prepregs reinforced with glass and carbon fibres and an aluminium alloy core are the new variant of the other types used by aerospace FML materials such as GLARE or CARALL. By using a thermoplastic matrix, they can be shaped by stamping processes, which allows for a more efficient production process than classical laminating methods such as vacuum bagging. In addition to the improved impact energy absorption efficiency, the metallic core can be utilised to effectively bond the composite part to adjacent metallic structures. This article presents the influence of the material configuration of fibre-metal laminates consisting of continuous fibre-reinforced thermoplastic outer layers integrated with a layer of metallic aluminium alloy inserts—a number of layers, type and direction of reinforcing fibres—on the static and fatigue flexural properties. In this study, eight laminate configurations were prepared using a one-step variothermal consolidation process. The results showed that in the three-point flexural fatigue test, the samples exceeded 106 cycles at stresses <30% of the static bending strength. Laminates with predominantly longitudinally reinforced layers showed the highest fatigue strength among the FML samples analysed. The type of reinforcing fibres and the number of layers were less affected on the analysed mechanical properties. PubDate: Mon, 13 Feb 2023 00:00:00 GMT
Abstract: The focus of this research work was predicting the fatigue life of mechanical components used for industrial and transport systems. To understand how the phenomenon of fatigue occurs in a material, the fatigue crack growth is studied. The purpose of this work was to create a graphical user interface (GUI) under Matlab to allow researchers to conduct the parametric studies of fatigue crack propagation to predict fatigue life. In this work, three models for fatigue crack propagation were used: those of Paris, Walker and Forman in order to study the three parameters: the Paris exponent m, load ratio R and hardness KIC, respectively. In addition, a novel model FCG was developed to study the influence of the hardening parameters (K′, n′) on fatigue crack propagation. The comparison of the simulation results with those in the literature shows good agreement. PubDate: Thu, 28 Jul 2022 00:00:00 GMT
Abstract: Rescue patrol hovercrafts must meet the basic condition – high reliability of use in extreme conditions. The introduction to the work shows damage to the propulsion system and the fan tunnel structure resulting from a fatigue fracture of the attachment wound to the propulsion unit hull. In this paper, the author describes some ways of improving the engine frame structure. In the first phase of the exploitation crack testing of the hovercraft frame, the probable causes of damage were determined. The necessary output data for analysis of the load course were obtained from the operating documentation. The approximate number of variable load cycles acting on the frame truss rod was determined. Using the comparative testing methods, the service life of the frame was estimated. Probable resonance frequencies of the vibrating bars in the truss were determined. Vibration tests of the power transmission assemblies were carried out, which allowed to determine the amplitudes and frequencies of free vibrations. Finally, a modification of the frame shifting the resonant frequency range was proposed. In conclusions, changes to the design and a schedule of inspections were proposed. The newly designed engine frame should have an extended service life. PubDate: Thu, 28 Jul 2022 00:00:00 GMT
Abstract: Methods of incremental manufacturing, i.e. 3D printing, have been experiencing significant growth in recent years, both in terms of the development of modern technologies dedicated to various applications, and in terms of optimizing the parameters of the process itself so as to ensure the desired mechanical and strength properties of the parts produced in this way. High hopes are currently being pinned on the use of highly penetrating types of radiation, i.e. synchrotron and/or neutron radiation, for quantitative identification of parameters characterizing objects produced by means of 3D printing. Thanks to diffraction methodologies, it is feasible to obtain input information to optimize 3D printing procedures not only for finished prints but also to monitor in situ printing processes. Thanks to these methodologies, it is possible to obtain information on parameters that are critical from the perspective of application of such obtained elements as stresses generated during the printing procedure itself as well as residual stresses after printing. This parameter, from the point of view of tensile strength, compression strength as well as fatigue strength, is crucial and determines the possibility of introducing elements produced by incremental methods into widespread industrial use. PubDate: Thu, 28 Jul 2022 00:00:00 GMT
Abstract: Refill Friction Stir Spot Welding (RFSSW) is a technology used for joining solid materials that was developed in Germany in 2002 by GKSS-GmbH as a variant of the conventional friction stir spot welding (FSSW) [1]. In the RFSSW technology, the welding tool consists of a fixed outer part and rotating inner parts, which are called a pin and a sleeve. The tool for RFSSW is designed to plasticize the material of the parts to be joined by means of a rotary movement. The design of the tool allows independent vertical movement of both elements of the welding tool. This allows obtaining spot welds without creating holes that could weaken the structure. The main advantage of RFSSW is the potential for replacing the technologies that add weight to the structure or create discontinuities, such as joining with screws or rivets. Thus, RFSSW has great potential in the automotive, shipbuilding and aviation industries. Furthermore, the technology can be used to join different materials that could not be connected using other joining methods. The main objective of this work is to understand the physical and mechanical aspects of the RFSSW method – including the residual stress state inside the weld and around the joint. The results of the investigations can help to determine optimal parameters that could increase the strength and fatigue performance of the joint and to prove the significant advantage of RFSSW connections over other types of joints. The work assumes the correlation of two mutually complementary investigation methods: numerical analyses and experimental studies carried out with diffraction methods. The comparison between numerical and experimental results makes potentially possible the determination of degree of fatigue degradation of the material by observing the macroscopic stress state and the broadening of the diffraction peak width (FWHM), which is an indicator of the existence of micro-stress related to the dislocation density and grain size. PubDate: Thu, 28 Jul 2022 00:00:00 GMT
Abstract: The greatest challenge of widely developed incremental manufacturing methods today is to obtain, as a result of the manufacturing process, such components that will have acceptable strength properties from the point of view of a given application. These properties are indirectly determined by three key characteristics: the level of surface residual stress, the roughness of the component and its porosity. Currently, the efforts of many research groups are focused on the problem of optimizing the parameters of incremental manufacturing so as to achieve the appropriate level of compressive residual stress, the lowest possible porosity and the lowest possible roughness of parts obtained by 3D methods. It is now recognized that determining the level of these three parameters is potentially possible using experimental X-ray diffraction methods. The use of this type of radiation, admittedly, is only used to characterize the surface layer of elements, but its undoubted advantage is its easy availability and relatively low cost compared to experiments carried out using synchrotron or neutron radiation. PubDate: Thu, 28 Jul 2022 00:00:00 GMT
Abstract: Material characterization and assessment is a crucial stage in most of aviation and aeronautical research and a basis for further design and testing of more complex aircraft elements and structures. Material test’s reliability can only be guaranteed by conducting them at independent and reliable laboratories, operating based on a management system assessed by a third-party such as the accreditation according to the ISO / IEC 17025 or NADCAP or having the qualification of the second-party based on specific customer requirements. This paper introduces basic requirements for material testing laboratories according to accreditation systems and describes its responsibilities as qualified and reliable testing suppliers. PubDate: Thu, 28 Jul 2022 00:00:00 GMT
Abstract: Despite of nearly 100 years of turbine engine development and design, blade vibrations remain a great engineering challenge. The rotating turbine blades’ vibrations lead to cyclic oscillations, which result in alternating stress and strain in harsh environments of high temperature and pressure. In modern aeroengines, high hot flow velocities might generate erosion and corrosion pitting on the metal surfaces, that leverage remarkably mean stresses. The combination of both mean and alternating stresses can lead to unexpected engine failures, especially under resonance conditions. Then, alternating stress amplitudes can exceed the safety endurance limit, what accelerates the high cyclic fatigue leading quickly to catastrophic failure of the blade. Concerning the existing state-of-the-art and new market demands, this paper revises forced vibrations with respect to excitation mechanisms related to three design levels: (i) a component like the blade design, (ii) turbine stage design consisting of vanes and blades and (iii) a system design of a combustor and turbine. This work reviews the best practices for preventing the crotating turbine and compressor blades from High Cyclic Fatigue in the design process. Finally, an engine commissioning is briefly weighed up all the pros and cons to the experimental validations and needed measuring equipment. PubDate: Mon, 06 Jun 2022 00:00:00 GMT
Abstract: The article presents the results of tests aimed at detecting discontinuities in the subsurface layer of elements intended for further processing. For the initial identification of discontinuities, the method of computed tomography was used. Based on the tomographic images of selected typical defects and measurements of the electrical conductivity of the material, the parameters for the eddy current tests were determined. A series of discontinuities in the subsurface layer to a depth of about 0.48 mm were detected. This allowed, at a given stage of machining, relevant elements to be selected for further processing. PubDate: Mon, 06 Jun 2022 00:00:00 GMT
Abstract: Processing of digital experimental data has become a key part of virtually every research project. As sensors get both more diverse and cheaper, the amount of information to be handled greatly increases as well. Especially fatigue failure modelling requires by its nature large numbers of samples to be processed, and visualised. The presented paper is based on analysis of load data gathered in flight on an unmanned aircraft. A few versions of an analysis program were developed and considered for the use case. Each implementation included ingesting the data files, creating transfer arrays and the “rain flow counting” algorithm. For the sake of the ease of use and functionality, the version based on Python programming language was selected for presentation. Short development iteration time of this approach allowed gaining new insights by tweaking parameters to better represent actual acquired data. Both the results and the software itself can be easily viewed in a web browser and run with modifications without the need to install any software locally. The developed software is meant as a demonstration of capabilities of open source computation tools dedicated to aerospace and mechanical engineering research, where they remain relatively unpopular. PubDate: Mon, 16 May 2022 00:00:00 GMT
Abstract: As one of the key components of the aircraft in terms of both operation and safety landing gears are of special interest of the aviation regulations. During the touch down landing gears need to dissipate as much of the energy as possible maintaining the lowest volume and weight as required by the aviation design restrictions. According to the aviation regulations landing gears have to be tested in order to prove the dissipation of the calculated landing energy and to evaluate actual loads acting on the fuselage via the mounting nodes of the landing gears. The tests need to replicate the real landing conditions as closely as possible – including the lift force (or lift) acting on the aircraft during landing. The lift force during landing is not sufficient to maintain the aircraft in flight but acts as the relief force to the aircraft weight resulting in lowering loads applied to the fuselage and decreasing landing energy needed to be dissipated. The lift force or lift has to be taken into account during laboratory tests of landing gears. The lift force needs to be simulated in all of the landing gears dynamic tests: performance optimization, proof of the operation for the certification, and the fatigue evaluation. There are two main methods of applying the lift during the tests: equivalent/effective mass or direct lift application. The latter is used at the Landing Gear Laboratory of the Lukasiewicz Research Network – Institute of Aviation (where author works on daily basis). The lift is applied by the pneumatic cylinders built in the test stand. Until recently the control of the lift force value was performed indirectly by the measurement of the pressure inside the pneumatic system. Recently the experimental direct measurement system using force transducers was introduced in order to directly measure the lift force during every test. In the presented paper, the author gives an overview of the lift force measurement system including its design and the results of the preliminary use evaluation. PubDate: Wed, 27 Apr 2022 00:00:00 GMT
Abstract: The purpose of the work presented was to evaluate the capabilities of digital radiography to detect cracks in the internal structure of MiG-29 vertical stabilizers. The test object was a stabilizer previously subjected to fatigue testing and partially torn down for the needs of visual inspection. An inspection of three regions containing cracked parts was performed, with use of a pulsed x-ray generator and digital detector array. The results confirmed the method could be used to detect cracks in an internal structure which could not be inspected with other methods without affecting the stabilizer’s integrity. PubDate: Tue, 22 Mar 2022 00:00:00 GMT
Abstract: The Modular Test Stand was developed and manufactured to decrease the cost of fatigue testing and reduce the time of its completion as well as to enable testing specimens under more complex load conditions. The stand consists of three connected sections, similar to a wing box, all being loaded in the same way. Thanks to that, several specimens can be tested simultaneously. This configuration requires that stress and strain distribution should be reasonably uniform, as assumed in the design stage. The structure can be loaded with bending or torsion. A whole section, selected structural node or a specimen mounted in the structure as well as a repair or a sensor can be a test object.Two stands, one for bending and one for torsion were prepared. This paper presents the verification of the assumed strain and stress distributions on the skin panels. The measurements were performed with the use of Digital Image Correlation (DIC) as well as strain gauges. DIC measurements were performed on one skin panel of the central section. Five strain gauge rosettes were installed on both panels of the one section. In addition, one rosette was applied to one skin panel in each of two other sections. Measurements were performed on the stand for torsion as well as on the stand for bending. The results of DIC analysis and strain gauge measurement during torsion show uniform shearing strain distributions on the panels. During bending, on the tensioned side, the strains obtained indicate quite uniform strain distributions. On the compressed side, local buckling of the skin panels results in high strain gradients. Strain levels obtained with the use of a DIC analysis and strain gauge measurements were similar. Moreover, horizontal displacements of markers in the spar axis during bending was determined based on a series of photographic. The deflection line obtained in this way has a shape similar to arc, which is characteristic of the constant bending moment.The stand was tested with torsional and bending loads in order to verify the design assumptions. The results of strain distributions on the skin panels with the use of DIC and strain gauges as well as the deflection line of the spar axis indicate that the Modular Test Stand performs as assumed and can be used for tests. PubDate: Fri, 23 Jul 2021 00:00:00 GMT
Abstract: The main design parameters that impact the fatigue of components are geometry, material and loading. Simulation with Finite Element Analysis (FEA) and tests on a vibrating table are often used to understand the dynamic behaviour of components and thus validate those items.Accelerated tests are used for the mission profile and test definition, as described in GAM-EG-13, MIL-STD-810F and RTCA DO-160E. The shock response spectrum (SRS) and the extreme response spectrum (ERS) allow for a comparison of the power spectrum density (PSD) and the acceleration factor applied in terms of fatigue severity through the fatigue damage spectrum (FDS). In addition, the hypothesis of linear damage accumulation enables the combination of several events for specifying a mission profile. Ultimately, the mission profile, which represents a usage that might span over several years, can be reduced to a shorter duration with a damage extraction technique. This is particularly useful for the definition of vibrating table specifications.An advantage of the virtual vibrating table is the reduction of the number of prototypes and the understanding of failure modes. To achieve this objective, finite element analysis in the frequency domain (harmonic analysis) is used and the structural stress response is evaluated with a PSD loading. A statistical model of rainflow allows assessing the damage on the components. The presentation also shows the effects of the damping factor on damage results. To achieve accurate results and define a Digital Twin, the correlation between test results and the finite element analysis is fundamental. Experimental modal analysis, based on the measured acceleration responses, helps to validate calculated modal frequencies and to assess the damping for each mode. This study shows the importance and the sensitivity on damping of the structural response, and in turn on fatigue. PubDate: Fri, 23 Jul 2021 00:00:00 GMT
Abstract: Friction Stir Welding joint quality depends on input parameters such as tool rotational speed, tool traverse speed, tool tilt angle and an axial force. Surface defects formation occurs when these input parameters are not selected properly. The main objective of the recent paper is to develop Discrete Wavelet Transform algorithm by using Python programming and further subject it to the Friction Stir Welded samples for the identification of various external surface defects present. PubDate: Fri, 23 Jul 2021 00:00:00 GMT
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