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.
{"title":"Laser Powder Bed Fusion and Selective Laser Melted Components Investigated with Highly Penetrating Radiation","authors":"Elżbieta Gadalińska, Łukasz Pawliszak, G. Moneta","doi":"10.2478/fas-2021-0008","DOIUrl":"https://doi.org/10.2478/fas-2021-0008","url":null,"abstract":"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.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2021 1","pages":"81 - 98"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44387410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Certification of Testing Laboratories – The Basis of Reliability Among Research Vendors in Aviation","authors":"Marzena Wichniarz","doi":"10.2478/fas-2021-0009","DOIUrl":"https://doi.org/10.2478/fas-2021-0009","url":null,"abstract":"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.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2021 1","pages":"99 - 105"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49466429","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Moneta, J. Jachimowicz, M. Pietrzakowski, Adam Doligalski, J. Szwedowicz
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.
{"title":"Insight Into Vibration Sources in Turbines","authors":"G. Moneta, J. Jachimowicz, M. Pietrzakowski, Adam Doligalski, J. Szwedowicz","doi":"10.2478/fas-2021-0005","DOIUrl":"https://doi.org/10.2478/fas-2021-0005","url":null,"abstract":"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.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2021 1","pages":"40 - 53"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69203714","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Lift Force Measurement in Landing Gears Dynamic Tests","authors":"Z. Skorupka","doi":"10.2478/fas-2021-0002","DOIUrl":"https://doi.org/10.2478/fas-2021-0002","url":null,"abstract":"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.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2021 1","pages":"8 - 16"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49356495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Application of Digital Radiography (Dr) in an Approach to Evaluate the Technical Condition of MiG-29’s Vertical Stabilizers","authors":"Rafał Luziński, P. Synaszko, K. Dragan","doi":"10.2478/fas-2021-0001","DOIUrl":"https://doi.org/10.2478/fas-2021-0001","url":null,"abstract":"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.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2021 1","pages":"1 - 7"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42378838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Research on Hovercraft – Fatigue Cracks in the Engine Frame","authors":"K. Szafran, M. Michalczyk","doi":"10.2478/fas-2021-0010","DOIUrl":"https://doi.org/10.2478/fas-2021-0010","url":null,"abstract":"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.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2021 1","pages":"106 - 115"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42147674","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Load Spectrum Analysis with Open Source Software – An Application Example","authors":"Marek S. Łukasiewicz","doi":"10.2478/fas-2021-0003","DOIUrl":"https://doi.org/10.2478/fas-2021-0003","url":null,"abstract":"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.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2021 1","pages":"17 - 30"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48285307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Elżbieta Gadalińska, A. Kubit, T. Trzepieciński, G. Moneta
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.
{"title":"Experimental and Numerical Stress State Assesment in Refill Friction Stir Spot Welding Joints","authors":"Elżbieta Gadalińska, A. Kubit, T. Trzepieciński, G. Moneta","doi":"10.2478/fas-2021-0006","DOIUrl":"https://doi.org/10.2478/fas-2021-0006","url":null,"abstract":"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.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2021 1","pages":"54 - 71"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45103972","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Low Cycle Fatigue (LCF) is one of most common mechanisms behind turbine blade failures. The reason is high stress concentration in notch areas, like fir-tree root groves, which can cause cyclic stress beyond the safe threshold. The stress levels strictly depend on the manufacturing accuracy of the fir-tree lock (for both fitted together: blade root and disk groove). The probabilistic study aimed at determination of stress was performed using Finite Element Method (FEM) simulation on a population of 1000 turbine models (disk + blades +friction dampers), where fir-tree lock dimensions were sampled according to the normal distribution, within limits specified in the documentation. The studies were performed for different manufacturing quality levels: 3-Sigma, 6-Sigma and 3-Sigma with tolerance ranges reduced twice. Based on the results, the probabilistic distributions, probabilities and expected ranges of values could be determined for: material plastification, stress, strain, LCF lifetime, etc. The study has shown how each tooth of the root is loaded and how wide a stress range should be expected in each groove. That gives information on how the definition of tolerances should be modified to make the construction more optimal, more robust, with lower likelihood of damage, taking into account the cost-quality balance. It also shows how the Six Sigma philosophy can improve the safety of the construction, its repeatability and predictability. Additionally, the presented numerical study is a few orders of magnitude more cost- and time-effective than experiment.
{"title":"Impact of Manufacturing Tolerances on Stress in a Turbine Blade Fir-Tree Root","authors":"G. Moneta, J. Jachimowicz","doi":"10.2478/fas-2020-0009","DOIUrl":"https://doi.org/10.2478/fas-2020-0009","url":null,"abstract":"Abstract Low Cycle Fatigue (LCF) is one of most common mechanisms behind turbine blade failures. The reason is high stress concentration in notch areas, like fir-tree root groves, which can cause cyclic stress beyond the safe threshold. The stress levels strictly depend on the manufacturing accuracy of the fir-tree lock (for both fitted together: blade root and disk groove). The probabilistic study aimed at determination of stress was performed using Finite Element Method (FEM) simulation on a population of 1000 turbine models (disk + blades +friction dampers), where fir-tree lock dimensions were sampled according to the normal distribution, within limits specified in the documentation. The studies were performed for different manufacturing quality levels: 3-Sigma, 6-Sigma and 3-Sigma with tolerance ranges reduced twice. Based on the results, the probabilistic distributions, probabilities and expected ranges of values could be determined for: material plastification, stress, strain, LCF lifetime, etc. The study has shown how each tooth of the root is loaded and how wide a stress range should be expected in each groove. That gives information on how the definition of tolerances should be modified to make the construction more optimal, more robust, with lower likelihood of damage, taking into account the cost-quality balance. It also shows how the Six Sigma philosophy can improve the safety of the construction, its repeatability and predictability. Additionally, the presented numerical study is a few orders of magnitude more cost- and time-effective than experiment.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2020 1","pages":"92 - 101"},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44603256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Kamińska, P. Synaszko, Patryk Ciężak, K. Dragan
Abstract An important factor having a negative impact on the technical condition of aircraft structure elements is the adverse effect of the atmosphere, which causes formation of corrosion in aircraft structures, especially in riveted lap joints. The electric potential difference between the sheet material and the rivet, in the presence of humid air, may cause electrochemical corrosion. The paper presents specimens that imitate the repair on the Mi-24 helicopter with the use of blind rivets in places where solid double-sided rivets could not be used. The aim of the research was to assess the corrosion resistance of lap joints with the use of single-sided and double-sided rivets. The analysis of corrosion resistance was carried out based on accelerated aging tests in a salt spray chamber. The salt chamber tests were aimed at determining the changes taking place in the specimens exposed to the marine environment. In the course of periodic observations changes in the mass of the specimens and in the form of corrosion losses were recorded. These activities were aimed at determining whether the exposure of specimens in the salt chamber causes electrochemical corrosion or pillowing. In addition, the specimens were subjected to static strength tests to assess the effect of corrosion on the strength properties of riveted joints.
{"title":"Analysis of the Corrosion Resistance of Aircraft Structure Joints with Double-Sided Rivets and Single-Sided Rivets","authors":"P. Kamińska, P. Synaszko, Patryk Ciężak, K. Dragan","doi":"10.2478/fas-2020-0006","DOIUrl":"https://doi.org/10.2478/fas-2020-0006","url":null,"abstract":"Abstract An important factor having a negative impact on the technical condition of aircraft structure elements is the adverse effect of the atmosphere, which causes formation of corrosion in aircraft structures, especially in riveted lap joints. The electric potential difference between the sheet material and the rivet, in the presence of humid air, may cause electrochemical corrosion. The paper presents specimens that imitate the repair on the Mi-24 helicopter with the use of blind rivets in places where solid double-sided rivets could not be used. The aim of the research was to assess the corrosion resistance of lap joints with the use of single-sided and double-sided rivets. The analysis of corrosion resistance was carried out based on accelerated aging tests in a salt spray chamber. The salt chamber tests were aimed at determining the changes taking place in the specimens exposed to the marine environment. In the course of periodic observations changes in the mass of the specimens and in the form of corrosion losses were recorded. These activities were aimed at determining whether the exposure of specimens in the salt chamber causes electrochemical corrosion or pillowing. In addition, the specimens were subjected to static strength tests to assess the effect of corrosion on the strength properties of riveted joints.","PeriodicalId":37629,"journal":{"name":"Fatigue of Aircraft Structures","volume":"2020 1","pages":"57 - 68"},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46135636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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