Palladium and tantalum aluminide coatings for high-temperature oxidation resistance of titanium alloy IMI 834

The present article explains the efforts made in developing new protective coatings based on palladium, tantalum, and aluminum with considerably improved oxidation resistance for effective protection of titanium alloy IMI 834. Systematic characterization was carried out on as-prepared as well as oxidized coatings and these results are presented. The performance of new coatings was evaluated by generating weight-gain data as a function of time followed by detailed characterization in order to confirm the ability of the coatings to prevent oxidation and alpha-case formation. The results showed that tantalum aluminide and simple aluminide coatings exhibit improved oxidation resistance when compared to palladium aluminide. Finally, the advantages of developed new coatings and the necessity of their use in modern gas turbine engines that allow the alloy to be used safely at high temperatures, which in turn would enhance the efficiency of gas-turbine engine-compressor sections, will be stressed.     

铝基复合材料焊接研究述评

铝基复合材料的比强度和比模量比铝合金材料高,在航天飞机、军用飞机、卫星、太空望远镜和汽车发动机领域获得得应用,要很好地应用铝基复合材料,通常取决于这种材料本身与其它金属材料的连接能力,焊接技术是连接铝基复合材料的有效途径,本文重点论述美国铝基复合材料的传统的焊接方法,研究现状、存在的问题和解决途径。     

High-efficiency 3 W/40 K single-stage pulse tube cryocooler for space application

Temperature is an extremely important parameter for space-borne infrared detectors. To develop a quantum-well infrared photodetector (QWIP), a high-efficiency Stirling-type pulse tube cryocooler (PTC) has been designed, manufactured and experimentally investigated for providing a large cooling power at 40 K cold temperature. Simulated and experimental studies were carried out to analyse the effects of low temperature on different energy flows and losses, and the performance of the PTC was improved by optimizing components and parameters such as regenerator and operating frequency. A no-load lowest temperature of 26.2 K could be reached at a frequency of 51 Hz, and the PTC could efficiently offer cooling power of 3 W at 40 K cold temperature when the input power was 225 W. The efficiency relative to the Carnot efficiency was approximately 8.4%.     

基于CAN总线控制系统的航天特种机械臂设计

航天特种机械臂具备精确操作和视觉识别的能力,在载人航天领域中广泛应用,为了在复杂环境中精准完成陆基装配任务,设计基于CAN总线控制系统的航天特种机械臂。从关节、连杆、驱动电机、锁紧制动器等方面,组装航天特种机械臂结构元件。装设航天特种机械臂控制器,在控制器中加设一个串行通信接口,将控制器连接到CAN总线中,配置CAN总线控制系统的通信协议,完成航天特种机械臂硬件结构设计。利用航天特种机械臂中传感器设备,检测航天特种机械臂实时位姿,补偿航天特种机械臂重力负载。根据机械臂工作任务,规划移动轨迹,在控制器的支持下,通过控制量的计算与通信,实现航天特种机械臂的控制功能。性能测试实验表明,设计基于CAN总线控制系统的航天特种机械臂平均位置和关节姿态角的控制误差分别为3.0m和0.32°,平均形变量为2.64m2,具有较好的控制性能和抗压性能。     

空天飞空天飞行器的自适应变论域模糊预测控制行器的自适应变论域模糊预测控制

考虑一类非线性不确定系统的变论域模糊预测控制问题.根据跟踪误差在线调整伸缩因子,使变论域模糊系统一致逼近被控对象中的未知干扰和不确定因素.通过引入鲁棒自适应控制器,消除了模糊建模误差,提高了系统的动态性能.基于泰勒展开的非线性预测控制律,避免了繁重的计算负担.基于Lyapunov理论,给出了伸缩因子的σ调整律,并证明了闭环系统一致最终有界.最后,将该算法用于空天飞行器(ASV)姿态控制系统的设计,仿真结果表明了该算法的有效性.     

Life-cycle reliability-based optimization of civil and aerospace structures

Today, it is widely recognized that optimization methodologies should account for the stochastic nature of engineering systems and that concepts and methods of life-cycle engineering should be used to obtain a cost-effective design during a specified time horizon. The recent developments in life-cycle engineering of civil and aerospace structures based on system reliability, time-dependent reliability, life-cycle maintenance, life-cycle cost and optimization constitute an important progress. The objective of this study is to present a brief review of the life-cycle reliability-based optimization field with emphasis on civil and aerospace structures.     

Investigation of the microwave-absorbing properties of Fe-filled carbon nanotubes

Carbon nanotubes encapsulated Fe nanowire composites were synthesized via pyrolyzing of ferrocene. The reflection loss (R.L.), matching frequency (f_m) and matching thickness (d_m) were calculated using the theory of the absorbing wall. The electromagnetic properties and microwave-absorbing characteristic effects by the encapsulation of metal Fe were investigated in a frequency range of 8-18 GHz. With matching thickness of 3.5 mm, the maximum reflection loss is about − 22.73 dB for the absorber. The bandwidth corresponding to the reflection loss below − 10 dB is more than 4.22 GHz. With increasing thickness, the peak value of the reflection loss shifts to a lower frequency.     

Soft Computing Algorithm to Data Validation in Aerospace Systems Using Parity Space Approach

This paper deals with the problem of data validation of an instrumentation system applied in the aerospace area. The fault diagnosis method used for the validation is based on the principle of the parity space approach. Residuals are generated thanks to the analytical redundancy relations given by the model and the important number of sensors. Indeed, we propose a procedure, which permits us to compute systematically all the redundancy equations for the residual generation phase. The additional concept, called residuals structuration, is necessary to isolate the detected faults. Finally, the data validation task consists in isolating the failing data and in sending only the valid information to a control system. An application to an aerospace system illustrates the proposed algorithm.     

Molecular design of in situ phosphatizing coatings (ISPCs) for aerospace primers

A novel chrome-free surface pretreatment and primer combined in one-step application for aircraft coating is described. First, a high-solids solvent-borne non-chromate epoxy primer (referred to as CD112) is developed. The formulation of CD112 system is based on epoxy/polyamide chemistry, Adheron’s proprietary anti-corrosive pigments, and a tightly packed passivating film made of fillers with different geometric shapes. The protective performance of CD112 has been tested at three independent laboratories and shown to pass a 3000 h salt spray resistance, compatible to its chromate counterpart, on both 2024-T3 Clad/Alodine 1000 and 7075-T6 Clad/Alodine 1000 aluminum alloys.

Second, a chrome-free acrylic emulsion for surface pretreatment of aluminum alloys is formulated, comprising an 60 nm particle size of acrylic resins, metal-chelating reagents, organofunctional silanes, and non-toxic anti-corrosive pigments. An 1 μm dry film is processed on 2024-T3 Bare Al panel (referred to as 2024-T3 Bare/AFP) and then coated with MIL-PRF-23377 Type I approved chromate-based primer. The electrochemical impedance spectroscopy (EIS) data indicate that 2024-T3 Bare/AFP show about 100 times more resistance than 2024-T3 Bare/Alodine 1200.

Third, two in situ phosphatizing reagents (ISPRs) were selected to formulate the in situ phosphatizing coating (ISPC) aerospace primers of MIL-PRF-23377 class N, and to promote the formation of a metal-phosphate layer at the molecular level. The ISPC technique combines a chrome-free surface pre-treatment and primer into a single-step application. The EIS data demonstrate that the ISPC CD112 primer on untreated 2024-T3 Al coupons shows 10–100 times more resistance than the control CD112 primer on 2024-T3 Bare/Alodine 1200. The chemistry of the simultaneous reaction of ISPRs catalyzing the curing of the paint film and forming the metal-phosphate layer at the interface will be illustrated.     

Creep behavior of Ti3Al–Nb intermetallic alloys

It is well known that Ti₃Al–Nb alloys are potential materials for aerospace applications. The creep property is an important consideration when materials are used at high temperature. In this article, the effect of microstructure of Ti–25Al–10Nb alloy on the creep property was investigated, and the creep property of Ti–25Al–10Nb alloy modified by small addition of silicon (0.2 at.%) or carbon (0.1 at.%) was observed. The alloy with the addition of molybdenum to replace part of niobium (2 at.%) was also studied. The experimental results show that the furnace-cooled Ti–25Al–10Nb alloy has superior creep resistance to the air-cooled Ti–25Al–10Nb alloy at 200 MPa, but exhibits poor creep resistance at 250 MPa or above. Small addition of silicon to the Ti–25Al–10Nb alloy may increase creep resistance. Small addition of carbon to the Ti–25Al–10Nb alloy may reduce creep resistance but raise rupture strain. Molybdenum is the most effective alloying element to increase creep resistance for the Ti–25Al–10Nb alloy. The creep mechanism of Ti–25Al–10Nb alloy is governed by dislocation climb.