DELAY-TIME MODEL BASED ON IMPERFECT INSPECTION OF AIRCRAFT STRUCTURE WITHIN FINITE TIME SPAN

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.

Corrosion Fatigue Life Prediction of Aircraft Structure Based on Fuzzy Reliability Approach

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.

Influence of environmental factors on corrosion damage of aircraft structure

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.

INVESTIGATIONS ON LASER SHOCK-PROCESSING (LSP) TO IMPROVE FATIGUE LIFE OF SMALL HOLE IN AIRCRAFT STRUCTURES

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.

THE RELIABILITY ANALYSIS OF AIRCRAFT STRUCTURES

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.

Accelerated corrosion test and corrosion failure distribution model of aircraft structural aluminum alloy

Based on corrosion damage data of 10 years for a type of aircraft aluminum alloy, the statistical analysis was conducted by Gumbel, Normal and two parameters Weibull distribution function. The results show that aluminum alloy structural member has the corrosion history of pitting corrosion—intergranular corrosion—exfoliation corrosion, and the maximum corrosion depth is in conformity to normal distribution. The accelerated corrosion test was carried out with the complied equivalent airport accelerated environment spectrum. The corrosion damage failure modes of aluminum alloy structural member indicate that the period of validity of the former protective coating is about 2.5 to 3 years, and that of the novel protective coating is about 4.0 to 4.5 years. The corrosion kinetics law of aluminum spar flange was established by fitting corrosion damage test data. The law indicates two apparent corrosion stages of high strength aluminum alloy section material: pitting corrosion and intergranular corrosion/exfoliation corrosion. The test results agree with the statistical fit result of corrosion data collected from corrosion member in service. The fractional error is 5.8% at the same calendar year. The accelerated corrosion test validates the corrosion kinetics law of aircraft aluminum alloy in service.

Cold expansion technology of connection holes in aircraft structures:A review and prospect

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.

Design of aircraft structures against threat of bird strikes

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.

Process-scheme-driven automatic construction of NC machining cell for aircraft structural parts

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.

REQUIREMENTS AND DESIGN METHOD FOR MATCHING AIRCRAFT GUNS WITH THEIR SUPPORTING STRUCTURE

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.

Digital Simulation of Full Scale Static Test of Aircraft

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.

Numerical Study on Aerodynamic Characteristics of Ducted Fan Aircraft

Based on investigations into the flow field of ducted fan aircrafts,structural parameters of duct are quantified.A three-dimensional model is established for numerical simulation,and adaptive Cartesian grid is used to mesh the model in order to improve calculation speed and solution accuracy.Three-dimensional Navier-Stokes equations are brought in to analyze different duct styles.Generalization of simulation results leads to several conclusions in duct aerodynamics to help design ducted fan aircrafts.

CALCULATING METHOD OF AERODYNAMIC HEATING FOR HYPERSONIC AIRCRAFTS

A new calculating method of aerodynamic heating for unsteady hypersonic aircrafts with complex configuration is presented.This method,which considers the effects of high temperature chemical non-equilibrium and the heat transfer process in thermal protection structure,is based on the combination of the inviscid outerflow solution and the engineering method,where the Euler solver provides the flow parameters on boundary layer edge for engineering method in aerodynamic heating calculation.A high efficient interpolation technique,which can be applied to the fast computation of longtime aerodynamic heating for hypersonic aircraft,is developed for flying trajectory.In this paper,three hypersonic test cases are calculated,and the heat flux and temperature distribution of thermo-protection system are shown.The numerical results show the high efficiency of the developed method and the validation of thermal characteristics analysis on hypersonic aerodynamic heating.

Design of Neural Network Variable Structure Reentry Control System for Reusable Launch Vehicle

A flight control system is designed for a reusable launch vehicle with aerodynamic control surfaces and reaction control system based on a variable-structure control and neural network theory.The control problems of coupling among the channels and the uncertainty of model parameters are solved by using the method.High precise and robust tracking of required attitude angles can be achieved in complicated air space.A mathematical model of reusable launch vehicle is presented first,and then a controller of flight system is presented.Base on the mathematical model,the controller is divided into two parts:variable-structure controller and neural network module which is used to modify the parameters of controller.This control system decouples the lateraldirectional tunnels well with a neural network sliding mode controller and provides a robust and de-coupled tracking for mission angle profiles.After this a control allocation algorithm is employed to allocate the torque moments to aerodynamic control surfaces and thrusters.The final simulation shows that the control system has a good accurate,robust and de-coupled tracking performance.The stable state error is less than 1°,and the overshoot is less than 5%.

基于激光点云的电力杆塔倾斜角度计算方法

本文旨在提出一种基于无人机激光点云数据的电力杆塔倾斜角度自动精准计算方法,用于解决电力杆塔人工巡检验收环节中倾斜度计算效率低下、过程繁琐、难度较高的问题。本方法利用无人机激光雷达获取复杂环境下的电力杆塔点云,采用分层密度统计与塔身结构提取方法,生成电力杆塔中轴方向线,并计算其与杆塔所处位置铅垂线的夹角,得到电力杆塔倾斜角度。为验证本方法的有效性,选取了不同地点4个待验收的杆塔进行实验,通过模拟仿真与影响因素分析,探索了电力杆塔倾斜角度计算的精度。结果表明,本方法对电力杆塔倾斜角度计算的平均绝对误差为0.017 4?,验证了其在电力杆塔人工巡检验收环节中倾斜度计算的有效性与可靠性。

武器装备轻量化结构正向设计方法及应用

为满足武器装备轻量化的迫切需求,提升装备结构优化设计水平,提出了一种代理模型辅助多目标优化的结构正向设计方法。按照从概念设计到参数优化设计的流程,通过优化信息交互和代理模型重构来实现结构多目标优化设计。以轻型车载高炮弹箱架优化设计为例,首先,根据拓扑优化获得的最佳传力路径,建立几何模型和有限元分析模型。其次,通过灵敏度分析缩减设计变量,建立以一阶模态频率和结构强度为约束、最小化质量和最大化刚度为目标的优化模型。然后,使用差分进化算法求解基于Kriging模型的多目标优化问题;在优化过程中,通过比较中间优化结果调整优化模型,并采用基于期望改进的填充样本策略重构代理模型。最后,兼顾结构轻量化和安全,筛选44组优化解中的3组优势方案与初始设计进行比较,结果显示:在满足弹箱架结构性能的前提下,重量分别可减轻31.2%、24.7%和21.8%;所提结构正向设计方法能够明显提升轻量化效果,也可为相关结构优化设计提供参考。

“飞机构造”实践教学改革探索

飞机结构及零部件特征决定了“飞机构造”这门飞行器制造工程专业基础课具有很强的理论性和工程技术性,教学过程中需要完善的实践教学资源做支撑。针对“飞机构造”实践教学过程中存在的问题,从教师自身素养、实践教学方法和资源等方面对“飞机构造”实践教学进行了改革探索。利用面向对象技术,基于Visual C#和ACCESS数据库平台,开发了飞机零部件三维数字化模型管理系统,实现了飞机零部件的浏览、增加、删除、修改和查找等操作功能,建立了数字航空馆。该系统在“飞机构造”课堂中得到了成功的应用,提高了学生对飞机零部件的感性认识,激起了学生探索飞机结构的好奇心,显著提升了教学效果。

柔翼结构飞行器智能控制系统关键技术与途径

柔翼结构飞行器具有轻质、空间集成、重复使用、有较大的阻力面积和升力系数等优点,可实现巡航飞行、低速驻空、再入返回、气动减速、定点归航、着陆缓冲等功能,是当前的研究热点。智能控制系统是柔翼结构飞行器飞航与回收着陆系统的核心技术之一,结合智能技术在控制系统中的应用研究与工程实践,对柔翼结构飞行器智能控制系统及其技术特征进行了分析;介绍了刚-柔组合体一体化控制与仿真、环境感知与健康状态在线评估、航迹规划与跟踪飞行控制、集群飞行控制、着陆与缓冲智能控制、智能硬件容错与重构等关键技术。对柔翼结构飞行器智能控制系统的未来发展进行了思考,提出了飞行环境的智能及柔性感知、气动参数的在线识别、多任务模式自主执行及控制系统的演进学习等发展建议,通过对智能控制技术持续不断地研究与实践,为柔翼结构飞行器系统的研制提供强有力的支撑。

柔性表皮及蜂窝支撑结构面外变形机制

变体飞行器可根据任务需求,自适应地改变气动布局,从而获得最优的飞行品质。由柔性表皮及蜂窝支撑结构复合而成的柔性蒙皮是实现变体飞行器构型变化的关键结构形式之一。但由于泊松效应的影响,柔性蒙皮在变形中易产生“凹陷”和“鼓包”等面外变形模式。为此,首先研究弹性模量、泊松比、表皮厚度、孔格尺寸、蜂窝构型等对面外变形的影响规律。然后基于孔格填充法,分析填充物与蜂窝壁在粘接良好和未粘接状态下的变形特性。结果表明:柔性蒙皮的面外变形与相关参数并非都呈现出线性变化关系;在蜂窝孔格内填充弹性材料,可抑制柔性蒙皮的面外变形,但填充材料是否与蜂窝壁粘接良好,对柔性表皮面外变形影响较大,在工程设计时,需重点关注。

高度修正实现刚度等效的梁结构有限元建模方法

民用飞机中对于梁结构的有限元建模,一般采用刚度等效方法将梁建成杆单元与剪切板单元的组合形式,这种有限元简化方法仅能保证截面刚度与真实截面刚度近似等效,但有限元中的截面面积与实际面积却相差较大,致使有限元分析的结果不能准确反映结构严重部位的应力情况。针对传统刚度等效有限元建模方法的不足,提出一种采用高度修正的刚度等效有限元建模方法;将该方法的计算结果与传统建模方法的计算结果、理论计算结果、试验测量结果进行对比。结果表明:本文提出的高度修正的有限元建模方法比传统杆板系建模方法更准确,与试验结果更接近;将该方法用于民用飞机结构有限元建模,能够对真实结构进行更准确地模拟,分析结果也更精确。