Chinese Journal of Aeronautics最新文献

Electrically Assisted Forming (EAF) technology has obvious advantages in material forming. To develop an effective constitutive model considering electrical effects, room temperature and electrically assisted quasi-static uniaxial tensile tests were conducted using ultrathin nickel-based superalloy plates with a thickness of 0.25 mm. The research focused on the two most widely recognized effects: the Joule thermal and the electric athermal effects. The mechanism of current action can be divided into two scenarios: one considering the Joule thermal effect only, and the other considering both effects simultaneously. Two basic constitutive models, namely the Modified-Hollomon model and the Johnson-Cook (J-C) model, were selected to be optimized through the classification of two different situations, and four optimized constitutive models were proposed. It was found that the J-C model with simultaneous consideration of the Joule thermal effect and electric athermal effect had the best prediction effect by comparing the results of these four models. Finally, the accuracy of the optimization model was verified by finite element simulation of the electrically assisted stretching optimization model. The results show that the constitutive model can effectively predict the temperature effect caused by the Joule heat effect and the athermal effect of current on the material.

The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high demands on its application. To achieve this objective, this study investigates the impact of three distinct brazing temperatures and five typical grain sizes on the brazed joints’mechanical properties and microstructure evolution process. Microstructural evolution analysis was conducted based on Electron Back Scatter Diffraction (EBSD), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), and Focused Ion Beam (FIB). Besides, the mechanical properties and fracture behavior were studied based on the uniaxial tension tests and in-situ tension tests. The findings reveal that the brazing joint’s strength is higher for the fine-grain capillary than the coarse-grain one, primarily due to the formation of a dense branch structure composed of G-phase in the brazing seam. The effects of grain size, such as pinning and splitting, are amplified at higher brazing temperatures. Additionally, micro-cracks initiate around brittle intermetallic compounds and propagate through the eutectic zone, leading to a cleavage fracture mode. The fracture stress of fine-grain specimens is higher than that of coarse-grain due to the complex micro-crack path. Therefore, this study contributes significantly to the literature by highlighting the crucial impact of grain size on the brazing properties of ultra-thin-walled Inconel 718 structures.

The electro-optical payloads on mobile platforms generally suffer undesirable vibrations generated by maneuvers and turbulence. These vibrations are in six degrees of freedom and cause line-of-sight jitters, resulting in image blurring and loss of tracking accuracy. In this paper, a Hexapod Vibration Isolation System (HVIS) is proposed and optimized to solve this problem. The optimization aims to centralize and minimize the natural frequencies of HVIS, for expanding the vibration isolation bandwidth and improving the vibration isolation in the higher frequency band. Considering that the design space for HVIS is limited and interfered with the frames of the mobile platform, a non-collision algorithm is proposed and applied in the optimization to obtain the feasible optimal design. The optimization result shows that the natural frequency bandwidth has been reduced by 42.9 %, and the maximum natural frequency is reduced by 30.2 %. The prototypes of initial and optimal designs are manufactured and tested. Both simulated and experimental results demonstrate the validity of the optimization, and the optimal design provides a maximum of 15 dB more isolation in rotation direction than the initial design.

Dry friction damping structures are widely-used in aero-engines to mitigate vibration. The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately and efficiently predict the forced response of frictionally damped structures. The state-of-the-art Multi-Harmonic Balance Method (MHBM) on quasi-3D contact model in engineering cannot precisely capture the kinematics on the friction interface although the efficiency is high. The full-3D contact model can describe the constitutive relationship of the interface in a more accurate manner; however, the efficiency and convergence are not guaranteed for large-scale models. In this paper, a semi-analytical MHBM on full-3D contact model is proposed. The original Trajectory Tracking Method (TTM) for evaluating the contact force is reformulated to make the calculation more concise and the derivation of the Analytical Jacobian Matrix (AJM) feasible. Based on the chain rule of derivation, the AJM which is the core to upgrade the performance is deduced. Through a shrouded blade finite element model, the accuracy and efficiency of the proposed method are compared with both the MHBM on full-3D contact model with numerical Jacobian matrix and the MHBM on quasi-3D contact model with AJM. The results show that the AJM improves significantly the efficiency of the MHBM on full-3D contact model. The time cost of the proposed method is in the same order of magnitude as that of the MHBM on quasi-3D contact model. We also confirm that the full-3D contact model is necessary for the dynamic analyses of shrouded blades. If one uses the quasi-3D model, the estimation relative error of damping can even reach 31.8% in some cases. In addition, the AJM also brings benefits for stability analysis. It is highly recommended that engineers use the MHBM on full-3D contact model for the dynamic analysis and design of shrouded blades.

As a key technology for space-based Earth observation and astronomical exploration, cooled mid-wavelength and long-wavelength Infrared (IR) detection is widely used in national defense, astronomy exploration, medical imaging, environmental monitoring, agricultural and other areas. The performances of IR detectors, including cut-off wavelength, detectivity, sensitivity and temperature resolution, plays a significant role in efficiently observing and tracking the low-temperature far-distance moving targets. Achieving optimal detection performance requires the IR detectors to operate at cryogenic temperatures. The future development of space-based applications relies heavily on the mid-wavelength and long-wavelength IR detection technologies, which should be enabled by the long-life cryogenic refrigeration and high-efficiency energy transportation system operating below 40 K, to support the Earth observation and astronomical detection. However, the efficiency degradation caused by the super low temperature brings tremendous challenges to the life time of cryogenic refrigeration and energy transportation systems. This paper evaluates the influence of cryogenic temperature on the infrared detector performances, reviews the features, development and space applications of cryogenic cooling technologies, as well as the cryogenic energy transportation approaches. Additionally, it analyzes the future development trends and challenges in supporting the space-based IR detection.

To investigate the distinct properties of the helicopter rotors during circling flight, the aerodynamic and dynamic models for the main rotor are established considering the trim conditions and the flight parameters of helicopters. The free wake method is introduced to compute the unsteady aerodynamic loads of the rotor characterized by distortions of rotor wakes, and the modal superposition method is used to predict the overall structural loads of the rotor. The effectiveness of the aerodynamic and the structural methods is verified by comparison with the experimental results, whereby the influences of circling direction, radius, and velocity are evaluated in both aerodynamic and dynamic aspects. The results demonstrate that the circling condition makes a great difference to the performance of rotor vortex, as well as the unsteady aerodynamic loads. With the decrease of the circling radius or the increment of the circling velocity, the thrust of the main rotor increases apparently to balance the inertial force. Meanwhile, the harmonics of aerodynamic loads in rotor disc change severely and an evident aerodynamic load shock appears at high-order components, which further causes a shift-of-peak-phase bending moment in the flap dimension. Moreover, the advancing side of blade experiences second blade/vortex interaction, whose intensity has a distinct enhancement as the circling radius decreases with the motion of vortexes.

An electromagnetic coil topology and its control strategy, which can be incorporated into the electromagnetic docking device, have been proposed for the relative roll control of two satellites in space. The target satellite and the chaser satellite are respectively embarked with four and six coils evenly arranged around the docking axis. All the coils on the target satellite are Direct Current (DC) energized, while the currents in the coils of the chaser satellite are regulated to achieve the relative roll control. The electromagnetic force/torque model is built by utilizing the frequently-used far field model. Based on the fundamental components extracted from that model, this paper proposes a real-time magnetic moment vector distribution formula that simply generates a constant roll torque. This paper not only presents an equation for calculating the relative roll angle through the Euler angles of two satellites, but also an equation that converts the roll torque setpoint to the setpoints of the coil currents. A 3-closed-loop positioning controller composed of angle, angular velocity, and current loop is developed. The proposed topology is verified by finite element simulation, and the control strategy is validated by dynamics simulation and ground-based tests.

Cylindrical rings with thin wall and high web ribs (CRTWHWR) are widely used as the key load bearing structures such as rocket body and space station cabin in aerospace field. However, it is still difficult to efficiently manufacture CRTWHWR with high performance because of their extreme geometry with thin-walled skins, high web ribs and large size. In this paper, a novel radial envelope forming process is put forward to efficiently achieve the plastic forming of CRTWHWR with high performance. Firstly, the principle of radial envelope forming process is clarified. Then, an efficient design method for the tool motion and geometry is proposed based on the reverse envelope principle, i.e., CRTWHWR is adopted to reversely envelope the tool and thus the tool which does not interfere with CRTWHWR can be efficiently obtained in a single operation. Finally, a reasonable 3D FE model of the radial envelope forming process of CRTWHWR is established and the radial envelope forming mechanism of CRTWHWR is comprehensively revealed. Through the FE simulation and experiments with material of plastic mud, a typical CRTWHWR with diameter of 300 mm, axial height of 192 mm, the maximum rib height of 25 mm, the minimum rib thickness of 3 mm and skin thickness of 5 mm is radial envelope formed, i.e., the ratio of the maximum rib height to the minimum rib thickness reaches 8.33, the ratio of the maximum rib height to skin thickness reaches 5 and the ratio of diameter to the minimum rib thickness reaches 100. The above results verify that the proposed radial envelope forming process has great potentials in efficiently manufacturing CRTWHWR with extreme geometry.