Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： In order to study the thermal stress of aircraft mechanical joint hybrid structure under extremetemperature of service environment , the theoretical formula for calculating bolt load of typical single lapjoints caused by thermal stress was derived based on the stiffness method considering the deformationcaused by temperature field.Aiming at the thermal stress analysis of complex large-size structures such aswall plates , the hybrid panel composed of Z. shaped aluminum alloy stringer and composite skin through 40bolts was used as the research object.'The two-dimensional simulation model of the panel structure was es-tablished based on the beam-shell combination unit and the thermal stress and nail load distribution rulesof the structure were obtained. In addition , through the low temperature environment test , the strain causedby thermal stress of composite materials and metals in the structure at different temperatures was analyzed.The results show that the finite element analysis results are consistent well with the test data and the planemodeling method can effectively reduce the modeling difficulty and calculation amount. The distribution of blot load is U-type and the maximum load magnitude is about 3500N, which provides a basis for structuralstrength analysis.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： Aiming at the complexity and uncertainty of the relationship between extreme environmentalstress and aircraft service risk assessment. The fault tree analysis method is used to systematically analyzeand discuss the correlation between aircraft accidents in service and extreme environmental stresses. First-ly , based on the statistical analysis of the database data related to aircraft accidents caused by extreme en-vironmental stress , an aircraft extreme environmental stress factor set and an aircraft extreme environmentalstress fault tree are constructed. 'Then ,according to the analysis of the action mechanism of extreme envi-ronmental stress and the mathematical model of severity , the probability of aircraft accidents caused by ex-treme environmental stress is calculated , the severity of direct correlation of extreme environmental stress isevaluated , and the correlation between extreme environmental stress and aircraft service accidents is pre-dicted.Finally , a method for analyzing extreme environmental stress accidents of aircraft in service is sum-marized.The research results show that icing, rain , crosswind , and fog have a great impact on the safe flightof service aircraft , which can provide support for aircraft maintenance , dispatch , and safe operation in ex-treme environments.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： In order to study the effect of environmental temperature on landing gear buffering performance,by taking an aircraft landing gear as the research object and considering the influence of temperature on airspring force and oil damping force in the landing gear dynamic model , this paper puts forward a landinggear dynamic analysis model considering the effect of temperature.'The model is verified by experiments ina temperature range ( -35 ℃ ~60 ℃).Combined with experimental data and simulation model ,the guid-ing values of air variable index and oil damping coefficient are given , and the influence law of temperatureon landing gear buffering performance is studied.The results show that the ambient temperature has a sig-nificant effect on the landing gear buffering performance , which is manifested as the change of the landinggear vibration load.And it is found that the gas in the buffer chamber is more sensitive to the influence oftemperature than the oil. At a low temperature , the change of air pressure and the change of oil physicalstate will make the buffer performance deteriorate significantly , and the change rate of the buffer pillar stroke reaches 25% . For landing gear that may work in complex environments , the influence of temperatureon air pressure and oil in the buffer should be fully considered in the design stage to ensure the safety ofaircraft landing.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： A temperature control method based on the change of test load is proposed for the extra-largespace climatic laboratory that has the feature of large change of test load and slow response of the controlprocess.First , the dynamic characteristic of the laboratory temperature control system is obtained by analy-zing the principle of the laboratory air temperature regulation process. Then , according to the control accu-racy and uniformity requirements of the laboratory field , the air flow partition compensation and dual stagetemperature control strategy of the refrigerant are formulated.Finally, the thermal load of the snow test con-dition is calculated , and the temperature cascade controller based on the thermal load feed-forward is de-signed.'The results show that the control method can quickly track the expected temperature curve duringthe process of temperature rise and fall , and the temperature change rate is kept stable at 3 ℃/h and thecontrol accuracy is kept ±2 ℃ when the steady state is reached.This control method can quickly compen-sate for the change of temperature caused by the load change in the test area , and the method meets the temperature control requirements of climatic tests.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： Ground flutter simulation test is a novel testing technology for aircraft flutter verification and aneffective supplement to the curent flutter verification test. In the process of actual flight , airerafi's dynamiccharacteristics and loads on the structure are constantly changing , especially for hypersonic vehicle affectedby aerodynamic heating.In this paper , a modeling method of time-varying parameter unsteady aerodynamicmodel is generated by the use of surrogate model.A ground flutter testing method of time-varying systembased on PID controller is established and verified by standard component test. The testing results showsthat the aerodynamic modeling method proposed can accurately obtain the aerodynamic model with time-varying characteristics , and the ground flutter testing method established can effectively respond to thetime-varying characteristics of the flutter system and obtain accurate flutter boundary.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： In order to study the ductile fracture mechanical properties of aviation aluminum alloy AA7075-T6 sheet under complex loading states , four tensile tests and hydraulic bulging tests with different stressstates were designed to obtain the hardening properties and fracture parameters of the material. Corre-sponding stress-strain curves were obtained through tensile tests at different strain rates and rolling direc-tions , and different hardening models and DF2016 ductile fracture criterion were used to characterize theirhardening behavior and fracture properties. The results show that the AA7075-T6 dogbone specimen hasgood repeatability when the strain rate is 1 s-' and 10 s -',and the stress-strain curve shows obvious jitterwhen the strain rate is 100 s -',but it does not increase with the increase of the strain rate.A significantstrain rate strengthening effect appears.Moreover , comparison of the stress-strain results in the seven roll-ing directions reveals that the tensile strength and fracture strain of different angles are basically the same.Therefore AA7075-T6 behaves as an isotropic and insensitive material with respect to strain rate in the study range. The Swift-Voce hardening model is used to predict the best results , and the DF2016 ductilefracture criterion can accurately predict the fracture position of AA7075-T6 in different stress states suchas shear , uniaxial tension, plane strain tension and equiaxed tension.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： In the process of aircraft service , it will experience complex dynamic processes such as groundtaxiing and maneuver etc.'The aireraft structure and airborne equipment will bear the individual or jointeffect of various dynamic loads during these processes. The induced structural dynamic problems are di-rectly related to the aircraft service safety and passengers’ride comfort. This paper sorts out the require-ments of structural dynamics in the military airplane structural integrity program and strength specification,as well as the airworthiness regulation of civil aircraft. The relationship between the structural dynamicsand R&D of aviation equipment is presented.'The main issues of aircraft structural dynamics are classifiedfrom the aspects of loads , structure , response and control.At last , the prospect of aircraft structural dynam-ics is briefly concluded considering the needs in aircraft equipment research and the newly developed vi-bration techniques.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： In onder to study the transmission loss of composite laminate under high frequency noise excita-tion , first , the laminate is equivalent to a single-layer anisotropic panel based on the general laminate theo-ry. Then, the transmission loss model of equivalent single-layer panel is established by SEA method , andmodal density , coupling loss factor , and other important input paramelers are calculated. Last , the trans-mission loss of laminate panel is obtained and compared with the experimental results. The results showthat the prediction results of transmission loss are basically consistent with the distribution trend of the ex-perimental values. However, due to the limitation of SEA method and the influence of stiffness equivalenton the inherent characteristics and radiation efficiency of laminate panel , the emor of low frequency band(200 H:-2 500 Hz) is above 3 dB. The high frequency band (2 500 Hz-10 000 Hz) prediction results a-gree well with the experimental values , and the error is within 3 dB. The two-dimensional equivalent SEAmodel of laminate panel can provide certain help for the rapid and accurate prediction of sound transmission characteristics of composite laminates under the excitation of high frequency noise in the process ofnoise reduction design and optimization.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Systemic experimental research was carried out on high- cycle fatigue behavior of FV520B steel based on the theory and calculation model of intrinsic dissipation. The experiment results show that the intrinsic dissipation of FV520B steel increases with the increase of the applied stress amplitude. Generally, the inflection point of intrinsic dissipation corresponds to the transition of the generation mechanism of intrinsic dissipation: from the reversible motion of the microstructure (the swing of dislocation lines between strong pinning points) to the combined effects of the reversible and irreversible motion of the microstructure (the generation of permanent slip, the unpinning from strong points and the multiplication of dislocation). And the stress amplitude corresponding to the inflection point is just the critical stress value inducing fatigue damage accumulation. Moreover, the results also indicate that FV520B steel subjected to constant stress amplitude keeps a relatively steady rate related to the applied stress amplitude and independent of the loading sequences. Additionally, the loading frequency has no effect on the fatigue damage per loading cycle. Fatigue failure will occur once the amount of the intrinsic dissipation, due to the irreversible motion of the microstructure, accumulates to a threshold value. And the energy threshold is found to be independent of the loading history.
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