Abstract: The bending and springback behaviors of sandwich sheets are more complicated than those of monolithic layer metallic sheet due to the extremely large difference in mechanical properties and in the gauges of polymer core and the skin sheet. In the present study, the bending and springback behaviors of aluminum-polymer sandwich sheets were investigated by using analytical method and conducting experiments and numerical simulations. A simplified analytical model was proposed to calculate the bending moments for sandwich sheet in unconstrained bending process through analyzing the strain and stress distributions of skin sheet and core materials. Then, the analytical model was applied to predict the springback of sandwich sheets after bending. Numerical simulations and experiments of unconstrained bending process for aluminum-polymer sandwich sheets were conducted to investigate the influences of mechanical properties of each layer and thickness ratio of two layers on the folding defects, neutral layer location, and springback. The results show that the neutral layer shifts dramatically toward the compression region of the specimen during bending. The folding angle mainly relates to the strength difference between the skin sheet and the core polymer. The springback angle of sandwich sheet is mainly determined by the mechanical properties of skin sheet.

Abstract: In this paper, the lattice Boltzmann method (LBM) is employed to simulate wave propagation in viscous media. LBM is a kind of microscopic method for modelling waves through tracking the evolution states of a large number of discrete particles. By choosing different relaxation times in LBM experiments and using spectrum ratio method, we can reveal the relationship between the quality factor Q and the parameter τ in LBM. A two-dimensional (2D) homogeneous model and a two-layered model are tested in the numerical experiments, and the LBM results are compared against the reference solution of the viscoacoustic equations based on the Kelvin-Voigt model calculated by finite difference method (FDM). The wavefields and amplitude spectra obtained by LBM coincide with those by FDM, which demonstrates the capability of the LBM with one relaxation time. The new scheme is relatively simple and efficient to implement compared with the traditional lattice methods. In addition, through a mass of experiments, we find that the relaxation time of LBM has a quantitative relationship with Q. Such a novel scheme offers an alternative forward modelling kernel for seismic inversion and a new model to describe the underground media.

Abstract: An ejectable flight data recorder for robust retention of flight data and aiding in locating an aircraft after an emergency situation comprises: a buoyant housing comprising an internal cavity, a door for access to at least a portion of the internal cavity, and an aerodynamic outer shape having a longitudinal axis; an energy-dissipating nose cone for reducing an impact load on the housing when the flight data recorder impacts a water surface; a nonvolatile memory configured to store flight data; a position sensor for detecting a geographic position of the flight data recorder; a radio transmitter; an antenna electrically coupled to the radio transmitter; a sustainable power system; and a hydrophone for acoustically tracking a sinking trajectory of the aircraft in a body of water.

Abstract: Purpose The present work aims to reveal the effect of deposition paths on transient temperature, transient stress, residual stress and residual warping in the electron beam freeform fabrication (EBF) process. Design/methodology/approach Six typical deposition paths were involved in the finite element (FE) simulations of EBF process by implementing a specially written program. Findings The results showed that the deposition path had a remarkable influence on heat transfer and transient temperature distribution in the scanning process, resulting in different residual stress and residual warping after cooling to room temperature. The largest and smallest temperature gradients were obtained from the zigzag and alternate-line paths, respectively. Meanwhile, the temperature gradient decreased with the increase of deposited layers. The optimum deposition path, namely, the alternate-line pattern, was determined with respect to the residual stress and residual warping. Originality/value Although some researcher revealed the importance of deposition path through FE analysis and experimental observation, their studies were usually confined within one type of deposition pattern. A complete investigation of typical deposition paths and comparison among them are still lacking in literature. To address the aforementioned gap, the present work started by extensive FE simulations of EBF process involving six representative deposition paths, namely, the alternate-line, zigzag, raster, inside-out spiral, outside-in spiral and Hilbert. For each deposition path, the transient temperature field, residual stress and residual deformation were obtained to optimize the deposition path.

Abstract: A semianalytical method hybridizing hierarchical theory and finite-strip method (FSM) is developed to analyze buckling behavior of composite laminate shells in this paper. The Legendre orth...

Abstract: Current research investigates the limitation of current cockpit design for Crew Alerting System (CAS) and Quick Reference Handbook (QRH), and proposes a potential design solution that might enhance crew performance. Using eye tracking device, an experiment was conducted based on Flight Simulator Software. Objective eye movement data as long as subjective feedback from participants were collected to evaluate the design. 24 participants experienced 4 scenarios with both traditional design and integrated design. Results demonstrated that participants never made error in locating the instructions by integrated design. It is due to the obvious fact that the instructions of integrated design will present itself, hence decrease the chance of executing the wrong NNC by eliminating the degree of choices. On the other hand, 75% of the participants experienced at least one error in finding the correct instruction, which is probably due to the limitation of QRH itself due to options too close in formatting which causes clicking the wrong page accidently. Furthermore, a trend was identified by eye movement patterns for longer fixation duration, smaller saccade amplitude, and less time fixated on instruction area occur in integrated design. Current research found that integrated design of CAS and QRH is superior in acquiring accurate solutions for emergent situations and processing the information presented compared with traditional design.

Abstract: A conventional Fowler flap is designed to improve the take-off and landing performances of an aircraft. Because the flight states of general aviation aircraft vary significantly. A Fowler flap with a double-sliding track has been designed, which is capable of changing airfoil camber while cruising and climbing as well as meeting low-speed performance requirements. The aerodynamic characteristics of the variable camber Fowler flap were studied by computational simulation, and cambering was found to be beneficial for improving the lift-to-drag ratio when the lift coefficient was larger than the critical value, below which decambering was more effective; this critical value differed somewhat under different conditions. Taking the mechanism into account, the take-off and landing configurations were optimized on the basis of the GA (W)-1 airfoil with a 30% chord Fowler flap. Compared with reference configuration, the maximum lift coefficient of optimized take-off configuration was increased by 6.6% as well as the stalling angle and the lift-to-drag ratio were increased by 1.3° and 7.58%, respectively. Moreover, the maximum lift coefficient of the optimized landing configuration was increased by 6.3%, and the stalling angle was increased by 1.1°; however, the nose-down pitching moment of both configurations increased. Similar results were attained on a general aviation aircraft wing/body combination. A 3D model of the variable-camber Fowler flap driving mechanism was established in a computer-aided design system, and the results showed that all design configurations could be achieved by the double-sliding track.

Abstract: Modularized small satellites will have even greater potential with better energy supply. In this paper, a PocketQube solar panel deployment and tracking system will be presented. The system is designed for a 3P PocketQubes. During the designing phase, trade-off analysis is done to meet the balance of weight, dimension and efficiency. Reliability, manufacturability, and cost are also considered from the beginning, as commercial production and launch are expected. The CAD design, dynamics analysis, motion simulation, and rendering for the project are undertaken by Solidworks, whereas Abaqus CAE is utilized for the finite element analysis of the vibration test of the panels. In the gimbal subsystem, we use two micro stepper motor to drive the panels via a two-axis gearbox, enabling the panels to track the sun omnidirectionally. In the panel subsystem, two types of customized spring hinges are designed. Robust and verified parts, such as burner resistors, are chose for the control and deployment system. After the continuous optimization process throughout the design phase, by comparing different manufacturing processes technologies, materials, and design details, the full scale prototypes of the gimbal subsystem were built and tested. In the end, the most feasible solution, as well as the suggestions for the development, were put forward.

Abstract: This provides precious experience and reliable reference data for future design. This paper introduces the analysis process of Fan-blade-out, and considers the effect of windmill load on the fatigue lifespan of the case. According to Extended Operations (ETOPS) in the airworthiness regulations, the fatigue crack of it is analyzed by the unbalanced rotor load, during FBO. Compared with the lifespan in normal work of the engine, this research provides valuable design experience and reliable reference data for the case design in the near future.

Abstract: The purpose of this paper was to investigate the damage tolerance of single-stiffener panels. The impact response and the influence of impact damage on compression behavior were studied. Barely visible impact damage (BVID) was introduced to the stiffener flange tip on the smooth side. By applications of visual inspections and C-scan, massive damage was detected. After the impact experiment, compression tests were carried on the intact specimens and impacted specimens. The experimental results reveal that impact damage has no significant effect on the buckling mode. but decreases the buckling load by about 10%. The results also show that impact damage has an important influence on the compression failure mechanism. Under the compressive loading, impact damage propagates inside the skin after the buckling, which is a trigger for final fracture of damaged stiffened panels. Consequently, the impact damage causes a dramatical decrease in the failure load by 34%, approximately.

Abstract: Aim at large aircraft power supply which use variable frequency ac power supply and has complex power system structure, the parameters test system needs to store the large amount of data, puts forward a data storage strategy based on the system time; To meet the testing requirements of voltage phase difference, three-phase voltage unbalance and other characteristic parameters, the article designs a measuring way behind on equipment synchronization trigger; Chooses the root mean square method as a means of voltage effective value calculation and analyzes the relationships about the calculation method between each cycle of sampling points and the relative error; Based on multi-channel measurement equivalent model of establishing the multiplexing card, analyzes the causes of errors in signal acquisition and put forward the solutions; Finally, testing on voltage parameters of a certain aircraft variable frequency ac power system, the test results show that the system is stable and reliable, it has reached the design requirements.

Abstract: Surfaces and objects surround us, and touching them is integral to everyday life. Pathogen contaminated surfaces (fomites) are known to transmit diseases. However, little is known about the ways and speed at which surfaces become contaminated. We found that under certain conditions, the number of contaminated surfaces grows logistically, corresponding to possible rapid transmission of infection. In such a surface network, pathogen can be transmitted great distances quickly—as far as people move. We found that the surface contamination network in aircraft cabins exhibits a community structure, with small communities connected by the aisle seatback surfaces and toilets, which are high-touch surfaces. In less than two to three hours, most high-touch surfaces in the cabin are contaminated, and within five to six hours nearly all touchable surfaces are contaminated. During short haul flight, aisle passengers have higher fomite exposure. This closely matches the spatial infection pattern of one reported inflight norovirus outbreaks. Our model is generally applicable to other crowded settings. The commonly repeated advice to “wash hands frequently” may be replaced in future by more strategic advice such as “clean surfaces right now”, or advice based on who should wash their hands, and when.

Abstract: For composite structure design, determining the relationships between failure time and mechanical properties in the full range of working temperatures is essential. Dynamic mechanical analysis (DMA) and tensile tests were performed to get the dynamic and static mechanical properties of resin 5228A respectively at various temperatures. The master curves of storage modulus and Young's modulus were constructed at selected reference temperature 25°C using closed form shifting (CFS) method based on the time-temperature superposition principle (TTSP). During the shifting procedure of storage modulus, corresponding time-temperature shift factors were obtained, which meet the Arrhenius equation very well. Finally, the master curves of transverse and longitudinal compressive strength were constructed at 25°C by shifting the compression tests data of unidirectional laminates CCF300/5228A horizontally with the time-temperature shift factors obtained previously. Results show that both dynamic and static mechanical properties of the resin 5228A are obviously time-temperature dependent, higher frequencies induce more elastic-like behavior, transverse and longitudinal compressive strength decreases significantly with increasing failure time.