According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfe...According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfect inspections, thresholds and repeated intervals are concerned in delay-time models. Since the suggestion by the existing delay-time models that the inspections are implemented in an infinite time span lacks practical value, a de- lay-time model with imperfect inspection within a finite time span is proposed. In the model, the nonhomogenous Poisson process is adopted to obtain the renewal probabilities between two different successive inspections on de- fects or failures. An algorithm is applied based on the Nelder-Mead downhill simplex method to solve the model. Finally, a numerical example proves the validity and effectiveness of the model.展开更多
As one kind of key anti-fatigue manufacture approaches with simplicity and effectiveness, the hole cold expansion technology satisfies the increasing needs for light weight and durability of aircraft structures.It can...As one kind of key anti-fatigue manufacture approaches with simplicity and effectiveness, the hole cold expansion technology satisfies the increasing needs for light weight and durability of aircraft structures.It can improve the fatigue life by several times at no additional weight conditions.The hole cold expansion technology has been widely used in manufacturing and repairing of both fighters and commercial aircraft, and has become a research hotspot in the strengthening technology.In recent years, hole cold expansion process methods, residual stress around expanded holes, the behavior of fatigue crack initiation and propagation, and fatigue lives after cold expansion are researched extensively through lots of experiments and finite element simulations.A review on the hole cold expansion technology research status in the last twenty years is presented in this paper.Via the analysis of the current characteristics and defects of the hole cold expansion technology, combined with the actual needs in design and manufacture of new-generation aircraft, development trends and novel research directions are presented for realizing precise and high-efficiency anti-fatigue manufacture.展开更多
In this paper, a method to design bird-strike-resistant aircraft structures is presented and illustrated through examples. The focus is on bird strike experiments and simulations. The explicit finite element software ...In this paper, a method to design bird-strike-resistant aircraft structures is presented and illustrated through examples. The focus is on bird strike experiments and simulations. The explicit finite element software PAM-CRASH is employed to conduct bird strike simulations, and a coupled Smooth Particles Hydrodynamic（SPH） and Finite Element（FE） method is used to simulate the interaction between a bird and a target structure. The SPH method is explained, and an SPH bird model is established. Constitutive models for various structural materials, such as aluminum alloys, composite materials, honeycomb, and foam materials that are used in aircraft structures,are presented, and model parameters are identified by conducting various material tests. Good agreements between simulation results and experimental data suggest that the numerical model is capable of predicting the dynamic responses of various aircraft structures under a bird strike,and numerical simulation can be used as a tool to design bird-strike-resistant aircraft structures.展开更多
Material performance of LY12CZ aluminum is greatly degraded because of corrosion and corrosion fatigue, which severely affect the integrity and safety of aircraft structure, especially those of lbe navy aircraft struc...Material performance of LY12CZ aluminum is greatly degraded because of corrosion and corrosion fatigue, which severely affect the integrity and safety of aircraft structure, especially those of lbe navy aircraft structure. The corrosion and corrosion fatigue failure process of aircraft structure are directly concerned with many factors, such as load, material characteristics, corrosive environment and so on. The damage mechanism is very complicated, and there are both randomness and fuzziness in the failure process. With consideration of the limitation of those conventional probabilistic approaches for prediction of corrosion fatigue life of aircraft structure at present, and based on the operational load spectrum obtained through investigating service status of the aircraft in naval aviation force, a fuzzy reliability approach is proposed, which is more reasonable and closer to the fact. The effects of the pit aspect ratio, the crack aspect ratio and all fuzzy factors on corrosion fatigue life of aircraft structure are discussed. The results demonstrate that the approach can be applied to predict the corrosion fatigue life of aircraft structure.展开更多
Composite materials are increasingly used in the aerospace industry.To fully realise the weight saving potential along with superior mechanical properties that composites offer in safety critical applications,reliable...Composite materials are increasingly used in the aerospace industry.To fully realise the weight saving potential along with superior mechanical properties that composites offer in safety critical applications,reliable Non-Destructive Testing(NDT)methods are required to prevent catastrophic failures.This paper will review the state of the art in the field and point to highlight the success and challenges that different NDT methods are faced to evaluate the integrity of critical aerospace composites.The focus will be on advanced certificated NDT methods for damage detection and characterization in composite laminates for use in the aircraft primary and secondary structures.展开更多
In order to enhance the NC programming efficiency and quality of aircraft structural parts （ASPs）, an intelligent NC programming pattern driven by process schemes is presented. In this pattern, the NC machining cell...In order to enhance the NC programming efficiency and quality of aircraft structural parts （ASPs）, an intelligent NC programming pattern driven by process schemes is presented. In this pattern, the NC machining cell is the minimal organizational structure in the technological process, consisting of an operation machining volume cell, and the type and parameters of the machining operation. After the machining cell construction, the final NC program can be easily obtained in a CAD/CAM system by instantiating the machining operation for each machining cell. Accordingly, how to automatically establish the machining cells is a key issue in intelligent NC program- ming. On the basis of the NC machining craft of ASP, the paper aims to make an in-depth research on this issue. Firstly, some new terms about the residual volume and the machinable volume are defined, and then, the technological process is modeled with a process scheme. Secondly, the approach to building the machining cells is introduced, in which real-time complement machining is mainly considered to avoid interference and overcutting. Thirdly, the implementing algorithm is designed and applied to the Intelligent NC Programming System of ASP. Finally, the developed algorithm is validated through two case studies.展开更多
Corrosion is one of the important structural integrity concerns of aging aircraft,and it is estimated that a significant portion of airframe maintenance budgets is directed towards corrosion-related problems for both ...Corrosion is one of the important structural integrity concerns of aging aircraft,and it is estimated that a significant portion of airframe maintenance budgets is directed towards corrosion-related problems for both military and commercial aircraft.In order to better understand how environmental factors influence the corrosion damage initiation and propagation on aircraft structure and to predict pre-corrosion test pieces of fatigue life and structural integrity of an effective approach,this paper uses the cellular automaton(CA)method to character the effect of electrolyte concentrations,dissolution probabilities,and temperature on the corrosion damage of a metal structure exposed to an aggressive environment,and the procedure for applying the local rules between the cells of the CA to simulate the corrosion damage evolution is formulated.The simulation results show that the different electrolyte concentrations,dissolution probabilities and temperature,the laws of the dissolution current with time are investigated and they obey the time power function.展开更多
Laser shock-processing (LSP) is of particular advantage for improving fa-tigue behavior of small holes and blind holes. Because there are not good accessibility andpassage, these holes cannot be treated by shot peenin...Laser shock-processing (LSP) is of particular advantage for improving fa-tigue behavior of small holes and blind holes. Because there are not good accessibility andpassage, these holes cannot be treated by shot peening or cold extrusion. The fatigue livesof aircraft aluminum alloy 2024-T62 are increased greatly by means of optimization oflaser shocking parameters. With 95 % confidence, the mean fatigue life of LSP specimensis 4. 35~7, 75 times larger than that of the un-shocked ones.展开更多
This paper presents a set of fundamental equations for reliability analysis of single-critical-point aircraft structures.The mathematical model is formulated by considering the following factors:the static strength of...This paper presents a set of fundamental equations for reliability analysis of single-critical-point aircraft structures.The mathematical model is formulated by considering the following factors:the static strength of structure,initial crack,the initiation and propagation and unstability of fatigue crack,the residual strength of structure,the statistical distribution of load,the periods of overhaul,accident damage,the communication of damage among fleets etc.Based on this mathematical model,the influence of these factors on the reliability can be quantitatively analyzed,and various criteria for fatigue design of aircraft structures can be evaluated from the aspect of reliability.展开更多
In aircraft structural dynamic design the matching of guns with their supporting structure is one of the most important tasks on which hinges the success or failure of the structural design. The design curves for matc...In aircraft structural dynamic design the matching of guns with their supporting structure is one of the most important tasks on which hinges the success or failure of the structural design. The design curves for matching guns with their supporting structure can be obtained from response calculations of the plate-spring system supporting the gun on the ground,the model structure tested on the ground and the actual structure.A set of matching curves is given for engineering application.Then,the matching design can be accomplished by means of impact load spectrograms so as to perform an optimal structural design and to make further improvements on dynamic design program.展开更多
In fatigue damage tolerance verification tests of aircraft structures,the simulation and loading of flight-byflight spectra require considerable time and resources.To improve the efficiency of load spectrum design and...In fatigue damage tolerance verification tests of aircraft structures,the simulation and loading of flight-byflight spectra require considerable time and resources.To improve the efficiency of load spectrum design and testing,an equivalent constant-amplitude spectrum design method for flight-by-flight spectra is proposed based on the equivalence of crack growth behavior.By combining the Paris crack growth model with the Walker stress ratio correction,the equivalent stress amplitude is directly calculated using structural parameters and load spectrum characteristics,enabling a rapid transformation from variable-amplitude spectra to constant-amplitude spectra.The original spectrum is discretized based on the load-exceedance curve,and the equivalence relationship between multilevel block spectra and constant-amplitude spectra is established.Taking a typical lower wing skin structure of a transport aircraft as an example,two equivalent spectra are designed and validated through fatigue crack growth tests on 2024-T351 center-hole plate specimens.The experimental results show that the fatigue life deviation between the equivalent spectra and the original flight-by-flight spectrum is within 10%,demonstrating the effectiveness of the proposed method.Moreover,the equivalent spectrum constructed under the condition of invariant mean flight stress exhibits higher equivalence accuracy.The influence of spectral shape on the equivalent stress amplitude is further analyzed,revealing that the equivalent stress amplitude increases with the spectrum shape coefficient.The proposed method provides a useful reference for load spectrum design in aircraft structural damage tolerance verification tests.展开更多
Full scale aircraft static test is a very important process of aircraft design, it is costly and time consuming. The testing accuracy and validity mainly depend on the rationality of the test scheme design. When the a...Full scale aircraft static test is a very important process of aircraft design, it is costly and time consuming. The testing accuracy and validity mainly depend on the rationality of the test scheme design. When the aircraft is being tested, the specimen＇s safety mainly depends on monitoring and understanding the testing data by way of evaluating the coherence with the digital simulation data synchyononsly. The test digital simulation can aid realizing above requirements and improving the test efficiency significantly during test scheme design stage or testing stage respectively. The key technologies and the solving methods of test digital simulation are presented and the application example is given.展开更多
Terminal airspace(TMA)is the airspace centering several military and civil aviation airports with complex route structure,limited airspace resources,traffic flow,difficult management and considerable airspace complexi...Terminal airspace(TMA)is the airspace centering several military and civil aviation airports with complex route structure,limited airspace resources,traffic flow,difficult management and considerable airspace complexity.A scientific and rational sectorization of TMA can optimize airspace resources,and sufficiently utilize the control of human resources to ensure the safety of TMA.The functional sectorization model was established based on the route structure of arriving and departing aircraft as well as controlling requirements.Based on principles of sectorization and topological relations within a network,the arrival and departure sectorization model was established,using tree based ant colony algorithm(ACO)searching.Shanghai TMA was taken as an example to be sectorizaed,and the result showed that this model was superior to traditional ones when arrival and departure routes were separated at dense airport terminal airspace.展开更多
Lattice composite structures as applied to fuselage barrel of a civil aircraft demonstrate high weight efficiency and capability to bear all external loads,typical for such kind of structures.One of the critical probl...Lattice composite structures as applied to fuselage barrel of a civil aircraft demonstrate high weight efficiency and capability to bear all external loads,typical for such kind of structures.One of the critical problems of lattice structures is low impact resistance,as such structure consists of unidirectional ribs,which residual strength drops severely even after an impact of a quite low energy.The impacts typical for fuselage barrel are low-velocity impacts of hail,small stones from the airdrome etc.with the level of impact energy up to 30–50 J.Low impact resistance of lattice composite fuselage structures leads to the necessity of its full protection against impacts.This means implementation of additional protective structure elements and thus increase of the structure weight.The scope of this study was to make a first approximation of the weight of protective elements for lattice fuselage structures based on impact tests of composite specimens with protection.The specimens consisted of unidirectional composite ribs with rectangular cross-section,manufactured by an industrial technology based on wet winding method,plastic protective hat put on an upper fringe of the rib and an elastic tape,wrapping together the rib and the hat.Specimens were put on a substrate to take into account the compliance of lattice structure and displacements of ribs at impact due to the quasi-static force.According to the standards of impact strength tests of aircraft components,one-inch impactor simulating a small stone,acting on a fuselage structure during aircraft take-off was used.The specimens were tested on low-velocity impact with energies from 10 to 50 J.Before and after the impact an ultrasound control was performed to check if any delamination occurred.For comparison,a number of unidirectional ribs with no protection were tested.展开更多
The reduction of the aircraft weight is a great challenge for constructors,allowing them to cut down on fuel consumption and to increase the load carrying.This can be achieved by improving the properties of materials ...The reduction of the aircraft weight is a great challenge for constructors,allowing them to cut down on fuel consumption and to increase the load carrying.This can be achieved by improving the properties of materials of aircraft parts.One of the most massive parts is the wing itself.In fact,according to a recent review of Aircraft Wing Mass Estimation Methods made by Dababneha and Kipouros(Aerosp Sci Technol,https://doi.org/10.1016/j.ast.2017.11.006,2017)an aircraft wing could reach 8811 kg(Megson in Aircraft structure for engineering students,3rd edn.Arnold,London,(1999)for an Airbus A320-200 and even 39,914 kg(Anderson in Fundamentals of aerodynamic,3rd edn.McGraw-Hill,Boston,1999)for a Boeing 747-100 since it is a long-range aircraft.Thus,it seems very interesting to act upon the material choice of wing components but without harming structure stiffness.In fact,composite integration has a direct impact on the stress and the weight of the wing which matters a lot in the conception of an aircraft wing.Such a complex problem requires indeed a multidisciplinary approach based on aerodynamics and structural analysis of both composite material and aluminum alloy.Solving this problem could be of great interest for both industrialists and researchers since it would lighten the path towards full composite wing integration.In this work,we propose a double-approach numerical method to study the effect of different composite materials integrated into aircraft wing skin stiffeners.By this way,this investigation aims to show the improvement given by composite materials to the structure and the achieved mass reduction after cautious integration,taking into consideration the stiffness of structure after load application.It also gives a method based on the best yield on weight ratio to compare the different possibilities of integrations to choose the most relevant material,its stacking and fibers orientations.For that,we relied on both analytical calculation and finite element analysis.A Matlab code was developed to determine structure response to loading such as longitudinal and shear stress and to estimate the global structure’s weight for different materials.We started by working on a wing made from the aluminum alloy AA2024 and then we integrated various composite materials like Glass fiber,S-glass/epoxy,and hm graphite/epoxy.Also,an investigation of the variability of stacking sequences and plies orientations was undertaken.As a result,we obtained a clear assessment of the potential of each material.We finally created,inspired by the Airbus technical data,an accurate finite-element model of an aircraft’s wing that served to study the structural resistance with Abaqus.Coherent results for the selected composite material and for its ply’s stacking and orientation were found.展开更多
The tilt rotor unmanned aerial vehicle（TRUAV） exhibits special application value due to its unique rotor structure. However, varying dynamics and aerodynamic interference caused by tiltable rotors are great technica...The tilt rotor unmanned aerial vehicle（TRUAV） exhibits special application value due to its unique rotor structure. However, varying dynamics and aerodynamic interference caused by tiltable rotors are great technical challenges and key issues for TRUAV＇s high-powered flight controls, which have attracted the attention of many researchers. This paper outlines the concept of TRUAV and some typical TRUAV platforms while focusing on control techniques. TRUAV structural features, dynamics modeling, and flight control methods are discussed, and major challenges and corresponding developmental tendencies associated with TRUAV flight control are summarized.展开更多
A theory model is established to describe the voltage-current responsefunction. The peak amplitude and the zero-crossing time of the transient signal is extracted as theimaging features, array pulsed eddy current (PEC...A theory model is established to describe the voltage-current responsefunction. The peak amplitude and the zero-crossing time of the transient signal is extracted as theimaging features, array pulsed eddy current (PEC) imaging is proposed to detect corrosion. The testresults show that this system has the advantage of fast scanning speed, different imaging mode andquantitative detection, it has a broad application in the aviation nondestructive testing.展开更多
Aircrafts damages caused by lightning strikes have been known since the early days of aviation.However,the physical effects on the aircraft structure are still being investigated.This work seeks to evaluate the lightn...Aircrafts damages caused by lightning strikes have been known since the early days of aviation.However,the physical effects on the aircraft structure are still being investigated.This work seeks to evaluate the lightning strike effects in the aluminum alloy 7075-T6.Samples were submitted to lightning strike simulation in laboratory and the damages evaluated through characterization techniques.Ultrasound and profilometry tests have shown material loss to 0.272 mm depth in the damaged region.In addition,it was detected the material accumulation occurrence in the damage vicinity of the region.Below the damage,it was found a region where metallurgical changes were identified.The tensile and microhardness tests results have shown reduction in the percentage elongation and hardness increasing in the material affected by lightning.These results are corroborated by the X-Ray Diffraction(XRD)and Rietveld Method(red line)that indicated an increasing in dislocation density and micro-deformation in the material matrix.Optical microscopy results have shown the presence of microcracks on the normal and cross-section surface of the samples damaged.The Energy Dispersive X-Ray Spectroscopy(EDXS)and Electron Backscattered Diffraction Test(EBSD)found coarse intermetallic phases and precipitates compounds with dimensions greater than 1 lm in length.They were responsible for nucleation of the microcracks that propagate along the material grain boundaries.展开更多
Reasonable and effective fatigue load spectrum is key of aircraft structural fatigue test.Two kinds of load spectra simplification approaches based on statistical consistent fatigue damage model are proposed in the pa...Reasonable and effective fatigue load spectrum is key of aircraft structural fatigue test.Two kinds of load spectra simplification approaches based on statistical consistent fatigue damage model are proposed in the paper.One method is to simplify the original multi-level load spectra to spectral load with fewer level and was verified by the experimental data of five levels and seven levels load spectra.The equivalent damage here is not equivalent fatigue life,but equivalent number of spectral blocks.Moreover,it was proved that a section of low stress load cannot be converted into the highest stress load considering equivalent damage.The other is to convert the life distribution under multi-level load spectra into that of constant amplitude spectrum according to a certain principle,that is,equivalent damage is achieved through equivalent fatigue life,and two groups of three levels spectral data were used for experimental verification.The results show that equivalent damage simplification approach of multi-level load spectra is feasible,and it achieve that the damage of one loading block before and after the simplification is equal in probability statistics.The life distribution of load simplified as constant amplitude spectrum is consistent with test data.The simplification method presented in this paper can be generalized and is a predictive engineering method which does not depend on experimental data.展开更多
A computing technology of the numerical simulations based on Abaqus code is presented in this paper for complex analysis of the uniaxial compressed stiffened composite panel,having local impact damage.The technology a...A computing technology of the numerical simulations based on Abaqus code is presented in this paper for complex analysis of the uniaxial compressed stiffened composite panel,having local impact damage.The technology allows simulating both dynamic deformations of the panel subjected to local impact and followed up by an axial static compression.A reliability of the developed computing technology is confirmed by comparison and closeness of the obtained numerical results and experimental data.Discrepancy of values obtained by the simulation from the corresponding experimental data is 8%for maximum contact force between the panel and impactor,7%for crack length on the opposite to the impact side of the panel and 10%for ultimate force,when the initially damaged panel is in compression.Also,the acceptable qualitative similarity of the modeled fracture mechanism and the shape to that observed in the experiments is observed.展开更多
基金Supported by the National Natural Science Foundation of China(61079013)the Natural Science Fund Project in Jiangsu Province(BK2011737)~~
文摘According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfect inspections, thresholds and repeated intervals are concerned in delay-time models. Since the suggestion by the existing delay-time models that the inspections are implemented in an infinite time span lacks practical value, a de- lay-time model with imperfect inspection within a finite time span is proposed. In the model, the nonhomogenous Poisson process is adopted to obtain the renewal probabilities between two different successive inspections on de- fects or failures. An algorithm is applied based on the Nelder-Mead downhill simplex method to solve the model. Finally, a numerical example proves the validity and effectiveness of the model.
基金the Fund of National Engineering and Research Center for Commercial Aircraft Manufacturing of China (No.SAMC12-JS-15-021)the Funding of Jiangsu Innovation Program for Graduate Education of China (No.CXLX12_0137)the Fundamental Research Funds for the Central Universities of China
文摘As one kind of key anti-fatigue manufacture approaches with simplicity and effectiveness, the hole cold expansion technology satisfies the increasing needs for light weight and durability of aircraft structures.It can improve the fatigue life by several times at no additional weight conditions.The hole cold expansion technology has been widely used in manufacturing and repairing of both fighters and commercial aircraft, and has become a research hotspot in the strengthening technology.In recent years, hole cold expansion process methods, residual stress around expanded holes, the behavior of fatigue crack initiation and propagation, and fatigue lives after cold expansion are researched extensively through lots of experiments and finite element simulations.A review on the hole cold expansion technology research status in the last twenty years is presented in this paper.Via the analysis of the current characteristics and defects of the hole cold expansion technology, combined with the actual needs in design and manufacture of new-generation aircraft, development trends and novel research directions are presented for realizing precise and high-efficiency anti-fatigue manufacture.
基金supported by Natural Science Foundation of China (No.11472225)
文摘In this paper, a method to design bird-strike-resistant aircraft structures is presented and illustrated through examples. The focus is on bird strike experiments and simulations. The explicit finite element software PAM-CRASH is employed to conduct bird strike simulations, and a coupled Smooth Particles Hydrodynamic（SPH） and Finite Element（FE） method is used to simulate the interaction between a bird and a target structure. The SPH method is explained, and an SPH bird model is established. Constitutive models for various structural materials, such as aluminum alloys, composite materials, honeycomb, and foam materials that are used in aircraft structures,are presented, and model parameters are identified by conducting various material tests. Good agreements between simulation results and experimental data suggest that the numerical model is capable of predicting the dynamic responses of various aircraft structures under a bird strike,and numerical simulation can be used as a tool to design bird-strike-resistant aircraft structures.
文摘Material performance of LY12CZ aluminum is greatly degraded because of corrosion and corrosion fatigue, which severely affect the integrity and safety of aircraft structure, especially those of lbe navy aircraft structure. The corrosion and corrosion fatigue failure process of aircraft structure are directly concerned with many factors, such as load, material characteristics, corrosive environment and so on. The damage mechanism is very complicated, and there are both randomness and fuzziness in the failure process. With consideration of the limitation of those conventional probabilistic approaches for prediction of corrosion fatigue life of aircraft structure at present, and based on the operational load spectrum obtained through investigating service status of the aircraft in naval aviation force, a fuzzy reliability approach is proposed, which is more reasonable and closer to the fact. The effects of the pit aspect ratio, the crack aspect ratio and all fuzzy factors on corrosion fatigue life of aircraft structure are discussed. The results demonstrate that the approach can be applied to predict the corrosion fatigue life of aircraft structure.
基金the support of NVIDIA Corporation with the donation of the Titan Xp GPU used for this researchsupported by EPSRC grant EP/R002495/1the European Metrology Research Programme through grant 17IND08。
文摘Composite materials are increasingly used in the aerospace industry.To fully realise the weight saving potential along with superior mechanical properties that composites offer in safety critical applications,reliable Non-Destructive Testing(NDT)methods are required to prevent catastrophic failures.This paper will review the state of the art in the field and point to highlight the success and challenges that different NDT methods are faced to evaluate the integrity of critical aerospace composites.The focus will be on advanced certificated NDT methods for damage detection and characterization in composite laminates for use in the aircraft primary and secondary structures.
基金supported by National Science and Technology Major Project (No.2012ZX04010051)
文摘In order to enhance the NC programming efficiency and quality of aircraft structural parts （ASPs）, an intelligent NC programming pattern driven by process schemes is presented. In this pattern, the NC machining cell is the minimal organizational structure in the technological process, consisting of an operation machining volume cell, and the type and parameters of the machining operation. After the machining cell construction, the final NC program can be easily obtained in a CAD/CAM system by instantiating the machining operation for each machining cell. Accordingly, how to automatically establish the machining cells is a key issue in intelligent NC program- ming. On the basis of the NC machining craft of ASP, the paper aims to make an in-depth research on this issue. Firstly, some new terms about the residual volume and the machinable volume are defined, and then, the technological process is modeled with a process scheme. Secondly, the approach to building the machining cells is introduced, in which real-time complement machining is mainly considered to avoid interference and overcutting. Thirdly, the implementing algorithm is designed and applied to the Intelligent NC Programming System of ASP. Finally, the developed algorithm is validated through two case studies.
基金supported by the National Natural Science Foundation of China(10962007)Key Project of Chinese Ministry of Education(209136)Ningxia Natural Science Foundation of China(NZ1027)
文摘Corrosion is one of the important structural integrity concerns of aging aircraft,and it is estimated that a significant portion of airframe maintenance budgets is directed towards corrosion-related problems for both military and commercial aircraft.In order to better understand how environmental factors influence the corrosion damage initiation and propagation on aircraft structure and to predict pre-corrosion test pieces of fatigue life and structural integrity of an effective approach,this paper uses the cellular automaton(CA)method to character the effect of electrolyte concentrations,dissolution probabilities,and temperature on the corrosion damage of a metal structure exposed to an aggressive environment,and the procedure for applying the local rules between the cells of the CA to simulate the corrosion damage evolution is formulated.The simulation results show that the different electrolyte concentrations,dissolution probabilities and temperature,the laws of the dissolution current with time are investigated and they obey the time power function.
文摘Laser shock-processing (LSP) is of particular advantage for improving fa-tigue behavior of small holes and blind holes. Because there are not good accessibility andpassage, these holes cannot be treated by shot peening or cold extrusion. The fatigue livesof aircraft aluminum alloy 2024-T62 are increased greatly by means of optimization oflaser shocking parameters. With 95 % confidence, the mean fatigue life of LSP specimensis 4. 35~7, 75 times larger than that of the un-shocked ones.
文摘This paper presents a set of fundamental equations for reliability analysis of single-critical-point aircraft structures.The mathematical model is formulated by considering the following factors:the static strength of structure,initial crack,the initiation and propagation and unstability of fatigue crack,the residual strength of structure,the statistical distribution of load,the periods of overhaul,accident damage,the communication of damage among fleets etc.Based on this mathematical model,the influence of these factors on the reliability can be quantitatively analyzed,and various criteria for fatigue design of aircraft structures can be evaluated from the aspect of reliability.
文摘In aircraft structural dynamic design the matching of guns with their supporting structure is one of the most important tasks on which hinges the success or failure of the structural design. The design curves for matching guns with their supporting structure can be obtained from response calculations of the plate-spring system supporting the gun on the ground,the model structure tested on the ground and the actual structure.A set of matching curves is given for engineering application.Then,the matching design can be accomplished by means of impact load spectrograms so as to perform an optimal structural design and to make further improvements on dynamic design program.
基金supported by the National Natural Science Foundation of China(No.52075244).
文摘In fatigue damage tolerance verification tests of aircraft structures,the simulation and loading of flight-byflight spectra require considerable time and resources.To improve the efficiency of load spectrum design and testing,an equivalent constant-amplitude spectrum design method for flight-by-flight spectra is proposed based on the equivalence of crack growth behavior.By combining the Paris crack growth model with the Walker stress ratio correction,the equivalent stress amplitude is directly calculated using structural parameters and load spectrum characteristics,enabling a rapid transformation from variable-amplitude spectra to constant-amplitude spectra.The original spectrum is discretized based on the load-exceedance curve,and the equivalence relationship between multilevel block spectra and constant-amplitude spectra is established.Taking a typical lower wing skin structure of a transport aircraft as an example,two equivalent spectra are designed and validated through fatigue crack growth tests on 2024-T351 center-hole plate specimens.The experimental results show that the fatigue life deviation between the equivalent spectra and the original flight-by-flight spectrum is within 10%,demonstrating the effectiveness of the proposed method.Moreover,the equivalent spectrum constructed under the condition of invariant mean flight stress exhibits higher equivalence accuracy.The influence of spectral shape on the equivalent stress amplitude is further analyzed,revealing that the equivalent stress amplitude increases with the spectrum shape coefficient.The proposed method provides a useful reference for load spectrum design in aircraft structural damage tolerance verification tests.
文摘Full scale aircraft static test is a very important process of aircraft design, it is costly and time consuming. The testing accuracy and validity mainly depend on the rationality of the test scheme design. When the aircraft is being tested, the specimen＇s safety mainly depends on monitoring and understanding the testing data by way of evaluating the coherence with the digital simulation data synchyononsly. The test digital simulation can aid realizing above requirements and improving the test efficiency significantly during test scheme design stage or testing stage respectively. The key technologies and the solving methods of test digital simulation are presented and the application example is given.
基金supported by the National Natural Science Foundation of China(Nos.U1233101,71271113)the Fundamental Research Funds for the Central Universities(No.NS2016062)
文摘Terminal airspace(TMA)is the airspace centering several military and civil aviation airports with complex route structure,limited airspace resources,traffic flow,difficult management and considerable airspace complexity.A scientific and rational sectorization of TMA can optimize airspace resources,and sufficiently utilize the control of human resources to ensure the safety of TMA.The functional sectorization model was established based on the route structure of arriving and departing aircraft as well as controlling requirements.Based on principles of sectorization and topological relations within a network,the arrival and departure sectorization model was established,using tree based ant colony algorithm(ACO)searching.Shanghai TMA was taken as an example to be sectorizaed,and the result showed that this model was superior to traditional ones when arrival and departure routes were separated at dense airport terminal airspace.
基金The financial support from the Ministry of Science and High Education of the Russian Federation(Project identification number RFMEFI62818X0009)is gratefully acknowledged.
文摘Lattice composite structures as applied to fuselage barrel of a civil aircraft demonstrate high weight efficiency and capability to bear all external loads,typical for such kind of structures.One of the critical problems of lattice structures is low impact resistance,as such structure consists of unidirectional ribs,which residual strength drops severely even after an impact of a quite low energy.The impacts typical for fuselage barrel are low-velocity impacts of hail,small stones from the airdrome etc.with the level of impact energy up to 30–50 J.Low impact resistance of lattice composite fuselage structures leads to the necessity of its full protection against impacts.This means implementation of additional protective structure elements and thus increase of the structure weight.The scope of this study was to make a first approximation of the weight of protective elements for lattice fuselage structures based on impact tests of composite specimens with protection.The specimens consisted of unidirectional composite ribs with rectangular cross-section,manufactured by an industrial technology based on wet winding method,plastic protective hat put on an upper fringe of the rib and an elastic tape,wrapping together the rib and the hat.Specimens were put on a substrate to take into account the compliance of lattice structure and displacements of ribs at impact due to the quasi-static force.According to the standards of impact strength tests of aircraft components,one-inch impactor simulating a small stone,acting on a fuselage structure during aircraft take-off was used.The specimens were tested on low-velocity impact with energies from 10 to 50 J.Before and after the impact an ultrasound control was performed to check if any delamination occurred.For comparison,a number of unidirectional ribs with no protection were tested.
文摘The reduction of the aircraft weight is a great challenge for constructors,allowing them to cut down on fuel consumption and to increase the load carrying.This can be achieved by improving the properties of materials of aircraft parts.One of the most massive parts is the wing itself.In fact,according to a recent review of Aircraft Wing Mass Estimation Methods made by Dababneha and Kipouros(Aerosp Sci Technol,https://doi.org/10.1016/j.ast.2017.11.006,2017)an aircraft wing could reach 8811 kg(Megson in Aircraft structure for engineering students,3rd edn.Arnold,London,(1999)for an Airbus A320-200 and even 39,914 kg(Anderson in Fundamentals of aerodynamic,3rd edn.McGraw-Hill,Boston,1999)for a Boeing 747-100 since it is a long-range aircraft.Thus,it seems very interesting to act upon the material choice of wing components but without harming structure stiffness.In fact,composite integration has a direct impact on the stress and the weight of the wing which matters a lot in the conception of an aircraft wing.Such a complex problem requires indeed a multidisciplinary approach based on aerodynamics and structural analysis of both composite material and aluminum alloy.Solving this problem could be of great interest for both industrialists and researchers since it would lighten the path towards full composite wing integration.In this work,we propose a double-approach numerical method to study the effect of different composite materials integrated into aircraft wing skin stiffeners.By this way,this investigation aims to show the improvement given by composite materials to the structure and the achieved mass reduction after cautious integration,taking into consideration the stiffness of structure after load application.It also gives a method based on the best yield on weight ratio to compare the different possibilities of integrations to choose the most relevant material,its stacking and fibers orientations.For that,we relied on both analytical calculation and finite element analysis.A Matlab code was developed to determine structure response to loading such as longitudinal and shear stress and to estimate the global structure’s weight for different materials.We started by working on a wing made from the aluminum alloy AA2024 and then we integrated various composite materials like Glass fiber,S-glass/epoxy,and hm graphite/epoxy.Also,an investigation of the variability of stacking sequences and plies orientations was undertaken.As a result,we obtained a clear assessment of the potential of each material.We finally created,inspired by the Airbus technical data,an accurate finite-element model of an aircraft’s wing that served to study the structural resistance with Abaqus.Coherent results for the selected composite material and for its ply’s stacking and orientation were found.
基金co-supported by the National Natural Science Foundation of China (Nos. 61503369 and 61433016)
文摘The tilt rotor unmanned aerial vehicle（TRUAV） exhibits special application value due to its unique rotor structure. However, varying dynamics and aerodynamic interference caused by tiltable rotors are great technical challenges and key issues for TRUAV＇s high-powered flight controls, which have attracted the attention of many researchers. This paper outlines the concept of TRUAV and some typical TRUAV platforms while focusing on control techniques. TRUAV structural features, dynamics modeling, and flight control methods are discussed, and major challenges and corresponding developmental tendencies associated with TRUAV flight control are summarized.
文摘A theory model is established to describe the voltage-current responsefunction. The peak amplitude and the zero-crossing time of the transient signal is extracted as theimaging features, array pulsed eddy current (PEC) imaging is proposed to detect corrosion. The testresults show that this system has the advantage of fast scanning speed, different imaging mode andquantitative detection, it has a broad application in the aviation nondestructive testing.
文摘Aircrafts damages caused by lightning strikes have been known since the early days of aviation.However,the physical effects on the aircraft structure are still being investigated.This work seeks to evaluate the lightning strike effects in the aluminum alloy 7075-T6.Samples were submitted to lightning strike simulation in laboratory and the damages evaluated through characterization techniques.Ultrasound and profilometry tests have shown material loss to 0.272 mm depth in the damaged region.In addition,it was detected the material accumulation occurrence in the damage vicinity of the region.Below the damage,it was found a region where metallurgical changes were identified.The tensile and microhardness tests results have shown reduction in the percentage elongation and hardness increasing in the material affected by lightning.These results are corroborated by the X-Ray Diffraction(XRD)and Rietveld Method(red line)that indicated an increasing in dislocation density and micro-deformation in the material matrix.Optical microscopy results have shown the presence of microcracks on the normal and cross-section surface of the samples damaged.The Energy Dispersive X-Ray Spectroscopy(EDXS)and Electron Backscattered Diffraction Test(EBSD)found coarse intermetallic phases and precipitates compounds with dimensions greater than 1 lm in length.They were responsible for nucleation of the microcracks that propagate along the material grain boundaries.
文摘Reasonable and effective fatigue load spectrum is key of aircraft structural fatigue test.Two kinds of load spectra simplification approaches based on statistical consistent fatigue damage model are proposed in the paper.One method is to simplify the original multi-level load spectra to spectral load with fewer level and was verified by the experimental data of five levels and seven levels load spectra.The equivalent damage here is not equivalent fatigue life,but equivalent number of spectral blocks.Moreover,it was proved that a section of low stress load cannot be converted into the highest stress load considering equivalent damage.The other is to convert the life distribution under multi-level load spectra into that of constant amplitude spectrum according to a certain principle,that is,equivalent damage is achieved through equivalent fatigue life,and two groups of three levels spectral data were used for experimental verification.The results show that equivalent damage simplification approach of multi-level load spectra is feasible,and it achieve that the damage of one loading block before and after the simplification is equal in probability statistics.The life distribution of load simplified as constant amplitude spectrum is consistent with test data.The simplification method presented in this paper can be generalized and is a predictive engineering method which does not depend on experimental data.
文摘A computing technology of the numerical simulations based on Abaqus code is presented in this paper for complex analysis of the uniaxial compressed stiffened composite panel,having local impact damage.The technology allows simulating both dynamic deformations of the panel subjected to local impact and followed up by an axial static compression.A reliability of the developed computing technology is confirmed by comparison and closeness of the obtained numerical results and experimental data.Discrepancy of values obtained by the simulation from the corresponding experimental data is 8%for maximum contact force between the panel and impactor,7%for crack length on the opposite to the impact side of the panel and 10%for ultimate force,when the initially damaged panel is in compression.Also,the acceptable qualitative similarity of the modeled fracture mechanism and the shape to that observed in the experiments is observed.
