Proceedings of the Institution of Mechanical Engineers,Part C: Journal of Mechanical Engineering Science

The most part of defects in composite structures carrying attached subelements is the disbond at the interface, as the skin/stringer sections. This is sometimes due to a nonoptimal manufacturing process or sometimes due to accidental object impacts during service. It has been verified that structural discontinuities within an elastic medium under mechanical loads can cause analogous discontinuities within the strain field. Starting from this analysis, the present work investigates the effect of artificially induced kissing bond areas just at the in the skin–stiffener interface of an aeronautical complex composite beam. This research uses longitudinal strain values, acquired at the locations where distributed fiber optic sensors are installed. The applied methodology uses different strain-based features providing local high edge observation both in time and spatial domains. Their autocorrelations are, in the end, computed to improve signal-to-noise ratio. The local high edge observation algorithm is proposed that proves its capability to monitor disbond being at the same time load and baseline independent.

As a new kind of active flow control technology, plasma flow control has a bright future, for its simple structure, fast response, and wide frequency band. The wind tunnel and flight tests were conducted with microsecond dielectric barrier discharge on a glider. For the tests, the microsecond pulse power supply and remote control system were designed and built. In the wind tunnel test, the flow separation on the glider wing surface can be controlled effectively, and static pressure at the leading edge pressure is decreases by 177%. The flow control effects under different pulse frequencies are compared, and the optimal pulse frequency for actuation is found to be 100 Hz. A significant hysteresis effect was observed with microsecond dielectric barrier discharge at small angle of attack (α ≤ 18°), which means the flow control effect can last more than 300 s after turning off the plasma actuation. In the flight test, the maximum roll angle decreases by 7.0°, and the maximum aileron deflection angle decreases by 9.4° with plasma actuation at both sides of the wing, which means the glider becomes more stable with microsecond dielectric barrier discharge. With unilateral actuation, the rolling moment generated by the plasma actuation is larger than that produced by the ailerons with the angle of attack within 12.94° ≤ α ≤ 29.77°, which shows strong rolling control ability of microsecond dielectric barrier discharge. The wind tunnel and flight tests results verified the flow control effect of microsecond dielectric barrier discharge, and paved the way for the plasma flow control technology to practical applications.

Wing's morphing leading edge, drooping in a seamless way, has significant potential for noise abatement and drag reduction. Innovative design methods for compliant skin and internal actuating mechanism, respectively, are proposed and validated through a mockup in this paper. For the skin, a collaborative optimization method is presented, which takes all design variables, continuous and discrete, into account simultaneously. Moreover, to overcome the drawback of conventional algorithm, which is insufficient for deformation control in critical regime, weight penalty is imposed on present objective function. On the other hand, an internal kinematic actuating mechanism is designed from an improved concept, of which positions of level-rod hinges are optimized in a larger zone to fit the deflection requirement. The test of mockup validates the above methods, and excellent morphing quality of the compliant skin proves the advancement of the collaborative optimization method. However, the design method of internal actuating mechanism needs further improvement, and the error induced deteriorates the final morphing quality of the mockup.

The scope of this work is to provide a critical review on the expectations about the morphing wing technology against the current open issues and showstoppers.

In synergy to other emerging and promising technologies, morphing is asked for bridging the evident gap between the current growth trend of the aerospace compartment and its impact onto the environment. The potential of morphing, in particular, its primary impact on the aerodynamic efficiency of the aircraft, primed the investigation of different technologies, achieving interesting results but often highlighting limitations and showstoppers against the airworthiness regulations.

The authors focus their attention on some specific aspects that characterize the morphing wing attachments and that may represent weakness points for the maturation of the technology: the load transmission of the movable parts to the supporting wing box, the way the flexibility–rigidity paradox is addressed by specific critical components (the skin), the scalability dependence of the morphing architectures, and the specific aeroelastic behavior of the nonconventional architectures.

It is a challenging work to design micro aerial vehicle with great aerodynamic performance because the tiny wingspan at low-Reynolds-number cannot provide lift efficiently. The aerodynamic configuration of a classic delta-wing paper airplane is investigated in the present work with numerical method to discover its potential for micro aerial vehicle designs. Furthermore, the effect of the ventral gap on the aerodynamic characteristics of the paper airplane is investigated herein. The stall angles of attack reach 37.5° and 40°, respectively, for ventral opened configuration and the closed one, and the maximum lift coefficient reaches 1.49 and 1.46. The ventral-opened configuration has negative pitching moment coefficient (−0.01431) even at 37.5° while the closed one has a positive coefficient (0.01402). The reason may be the gap leads to a strong back-flow vortex before the trailing edge in the ventral gap which produces a strong nose-down moment. Generally, the ventral gap improves lift and dramatically influences the longitudinal stability compared with the one without it.

The present work studies the aerodynamic performance of a small-scale rotor in tilting transition states through wind tunnel tests and numerical simulations. Firstly, the test platform for the rotor aerodynamics is built up, and the Computational Fluid Dynamics (CFD) model of flow field around the rotors is established based on the multiple reference frame method. Secondly, the effects of flow velocity, tilt angle and advance ratio on the aerodynamic performance of the rotor are investigated using both the numerical simulation and the wind tunnel test. It is found that for the Model 8038 rotor with maximum effeciency of 0.567 at advance ratio of 0.43, the rotor thrust coefficient increases with the increase of the Reynolds number. At Reynolds number of 410 thousand to 820 thousand, the thrust coefficient increases slightly with the increase of the rotating speed. The results also show that the thrust coefficient decreases with the increase of the advance ratio. With high-speed airflow and relatively low-speed rotation, “windmill” phenomenon is found in the experiment. The tilting of the rotor from level flight to hovering increases the thrust coefficient. Highly dependency of the tilt angle on the thrust coefficients at given advance ratios is found in the wind tunnel tests.

With the prospective of developing an integrated monitoring system aimed at assessing whether a landing gear has experienced hard impact during the approach, a dedicated method is developed aimed at determining vertical speed by means of strain measurement via FBG strain sensors. Representative impacts on simple structural elements have been reproduced in laboratory, as aluminum slender beams of different lengths were dropped from given heights onto a steel plate base. Contact velocities have been estimated by deformations detection.

A novel convertible unmanned aerial vehicle (UAV) with four tiltable rotors and a tandem-wing system has been developed. Considering the aerodynamic effect caused by the rotor-induced velocity, a mathematical model that contains the traditional free airstream analysis and rotor-induced effect analysis is proposed, from which the precise equilibrium point of the control inputs and states can be derived. Moreover, a control allocation algorithm is designed to provide the mapping relationship between traditional input variables and specific input variables of the UAV, so that the complicated mathematical model can be linearized for the design of model predictive control (MPC) system. In order to handle the control input constraints of the UAV system, an MPC system is applied for the trajectory tracking during the cruising phase. The simulation results demonstrate that the proposed model predictive control system has stability, accuracy without a random disturbance and quick response capabilities with a random disturbance during cruising trajectory tracking, which are in high demand for the quick UAV flight system.

Because of the advantages of light weight, small size, and good maneuverability, the bio-inspired micro aerial vehicle has a wide range of application prospects and development potential in military and civil areas, and has become one of the research hotspots in the future aviation field. The beetle’s elytra possess high strength and provide the protection of the abdomen while being functional to guarantee its flight performance. In this study, the internal microstructure of beetle’s elytra was observed by scanning electron microscope (SEM), and a variety of bionic thin-walled structures were proposed and modelled. The energy absorption characteristics and protective performance of different configurations of thin-walled structures with hollow columns under impact loading was analyzed by finite element method. The parameter study was carried out to show the influence of the velocity of impactor, the impact angle of the impactor and the wall thickness of honeycomb structure. This study provides an important inspiration for the design of the protective structure of the micro aerial vehicle.

Functionally graded material (FGM) has an important application prospect in aircraft engineering, especially in smart aircraft. The dynamic behavior of FGM has been widely investigated so far but more work is needed for the porous FGM pipes conveying fluid. In this paper, a sensible pore distribution function related with the volume fraction of metal and ceramic is proposed for the dynamic modeling of porous FGM pipes conveying fluid. The maximum porosity and its corresponding position are taken into account in the present mechanical model. The material properties of the porous pipes are temperature dependent and can be affected by pore distribution. The governing equation of the porous FGM pipe is derived and then the exact solution of post buckling is obtained. The nonlinear primary resonance is determined by the multiple scale method. It is shown that the effect of the pore distribution is very significant on the post buckling behavior and nonlinear primary resonance of the porous FGM pipes. The current work is very helpful in understanding the influence of pore distribution on static and dynamic behavior of pores FGM structures in engineering practice.

The poor real-time performance and target occlusion occurred easily when the UAV was tracking the target. In this paper, a target tracking method based on the Back Propagation neural network fusion Kalman filter algorithm was developed to solve the position prediction problem of the UAV target tracking in real time. Firstly, the target tracking algorithm was used to acquire the center position coordinates of the target on the onboard computer, and then the coordinate difference matrix was constructed to train the BP neural network in real time. Secondly, when the target was occluded by the obstacles judged by the Bhattacharyya coefficient, the BP neural network fusion Kalman filter algorithm was used to accurately predict the center position coordinates of the occluded target. Then the flight speed of UAV was calculated by the deviation between the coordinates of the target and the image center. Finally, the velocity command was sent to the UAV by the onboard computer. The experimental results shown that the target position predicted by BP neural network fusion Kalman filter algorithm was more accurate and robust in predicting the center position coordinates of the target, and the UAV can track the moving target on the ground stably.

Rocket-based combined-cycle (RBCC) powered vehicles have been widely recognized as the most promising aircraft solution that could dramatically reduce the cost of space transportation. Researchers and scientists worldwide have conducted considerable overall design researches to cope with the challenges in RBCC development including mode transition, thermal protection and thrust enhancement. According to the way to orbit and the configuration characteristics, the hypersonic aircraft powered by RBCC engine are classified as four categories: single-stage-to-orbit (SSTO) two-dimensional configuration, SSTO axisymmetric configuration, two-stage-to-orbit (TSTO) two-dimensional configuration, and TSTO axisymmetric configuration. This paper systematically presents the development of the conceptual design of RBCC-powered vehicles. Both the structural and operating key parameters like the weight distribution, the RBCC propulsion performance and take-off mode, et al. are introduced in detail. On this basis, a comparative analysis of the advantages and disadvantages of the orbit model, the configuration selection and takeoff modes are conducted. In addition, the application prospect and technology development direction for hypersonic aircraft are also discussed. At the same time, the lessons that can be drew from previous hypersonic vehicle concept design are explored.

This study uses large eddy simulation to investigate the flow characteristics of a centrifugal pump impeller with sinusoidal flow rate and constant rotational speed. Five different oscillation frequencies (f/f₀ = 1.0, 1.2, 1.5, 2.0, and 3.0, where f₀ indicates one-ninth of the rotational speed) are selected to isolate the influence of oscillation frequency on the flow characteristics. Studies show that the pressure deviation between dropping and rising stages concentrates at the impeller inlet at instantaneous 0.5 Q_d (Q_d is the design load), and its value increases with the increase in oscillation frequency. The lowest period of many flow characteristics, including pressure fluctuation and head, equals to that of flow rate. The differences in pressure fluctuation between adjacent channels decreases with the increase in oscillation frequency. The first and second dominant frequencies of pressure fluctuation are mainly affected by the oscillation frequency in the nonstall passage, and they have an important relationship with the stall vortex in the stall passage. With the increase in oscillation frequency, the amplitude of lowest order head pulsation increases, and the high order head pulsation gradually weakens. The average head is approximately 2.36 m.

The fused fabrication process (FFF), is one of the most popular additive manufacturing technologies used for prototyping and production applications. On the other hand, poor mechanical characteristics significantly impact the application of FFF parts, and a variety of process parameters can influence the effectiveness of parts produced with FFF. Infill density, layer thickness, print speed, and extrusion temperature are the essential FFF parameters for fabricating parts and the dimensional integrity of printed specimens. This research aims to examine the functional performance of ABS fabricated through FFF. The study’s various variables include extrusion temperature (230°C, 240°C, and 220°C), feed rate (20, 35, and 50 mm/s), and layer height (0.1, 0.15, and 0.2 mm). Based on various combinations, elongation at break, energy, tensile strength, and compressive strength will be assessed. The measured lowest tensile and compressive strengths are 25.252 and 38.52 MPa, respectively, and highest tensile and compressive strengths are 33.96 and 185.94 MPa, respectively. As a result, changing the different process variables increases tensile strength by 34.49% and compressive strength by 382.71%. Fractography analysis is also performed to understand the failure modes of specimens, indicating pulling, necking, failure of raster’s, and voids for the considered specimens. To examine the dependency and relationship of the tensile and compressive strength on the process parameters, statistical analysis is performed using ANOVA, Taguchi’s L27 array design of experiment, and regression analysis. It indicates that layer height has the most significant influence on tensile and compressive strength, followed by extrusion temperature and feed rate.

Silicon carbide particles reinforced aluminum matrix composites are widely used in national defense and related high-end technology fields due to their excellent mechanical properties. To explore the milling mechanism and tool wear mechanism of low-volume SiCp/Al composites in high velocity milling, the milling experiments for 20% volume SiCp/Al2009 composites were performed using a polycrystalline diamond (PCD) tools. A three-dimensional milling model of SiCp/Al composite was established considering the random distribution of SiC particles, the influence of milling parameters on surface quality was comprehensively analyzed and its cutting mechanism was described, and the wear forms and mechanism of PCD tools were revealed during milling of SiCp/Al composites. The result showed that the cutting depth is the main factor affecting the machined surface quality, followed by the spindle speed, and the feed rate has the smallest effect on it. It was observed that when spindle speed (n) was 17,000 r/min, the feed rate (f) was 8 mm/min, the depth of cut (a_p) was 0.04 mm, the surface roughness value was the smallest, Ra was 0.056 μm. The surface morphology was mainly manifested as pits, cracks, burrs, and so on, subsurface defects included particle breakage, peeling, and matrix cracks, and the tool wear forms included chipping, flaking, and bond wear.

The sealing performance is a critical characteristic of the stop valve used in an 11000-m manned submersible, while it is a challenge when the pressure difference at the valve port reaches 120 MPa. Previous studies have mainly focused on the effect of surface microtopography, such as the surface roughness, on sealing performance. They believed that rougher surfaces will result in more severe leaks. However, in the sealing experiments of two stop valves with different materials and surface roughness in this paper, the relationship between surface roughness and sealing performance is inconsistent with existing research. There should be another factor that affects the sealing performance of the stop valves more strongly. So a new sealing principle considering the roundness error is proposed. The sealing force, which is determined by the environmental pressure, creates radial deformation on the valve port. The radial deformation of the valve seat is analyzed by a validated finite element analysis (FEA) at various environmental pressures. Then the critical environmental pressure at which the leak stops is obtained when the radial deformation is greater than the roundness error, which is measured. The results show that the critical environmental pressure obtained by FEA is very close to that obtained by experiment. So the consideration of the roundness error of the valve seat is accurate and helpful to the research on the sealing performance of the ultra-high pressure stop valves, and the sealing performance of the ultra-high pressure stop valve can be easily evaluated by FEA.

Herein, MWCNTs/Al6082 composites were produced using a stir casting technique, and their tribological behavior was studied in as-cast and T6 heat-treated conditions using a pin-on-disk tribometer at a sliding speed of 2 m/s (fixed) and varying applied load (40, 60, and 80 N) and sliding distance (500–3000 m). Morphology of composites and worn-out surfaces were studied using a scanning electron microscope (SEM). Linear increment in wear rate was observed with sliding distance up to transition limit and then upsurged drastically beyond that limit. At 40 N, a protective layer started forming between the disk and surface of pin, which reduced coefficient of friction (COF), and wear mechanism was abrasion and oxide. Annihilation of protective layer at higher load increased COF and observed wear mechanism was adhesion and delamination. Wear resistance of alloy and nanocomposites was enhanced by heat treatment due to the strengthening of matrix. Wear rate of Al matrix was reduced with MWCNTs due to their self-lubricating property.

The roughness effects on the wheel-rail contact problem is an essential topic. In this paper, a new analytical-numerical model has considered assessing the specifications of a rough surface contact problem. The new model includes asperities and strain hardening effects together. Consideration of these assumptions is more realistic in comparison to similar simplified works. In this work, the effects of material properties variation on a contact problem realize. Besides, considering the strain hardening effects, the contact results for wheel-rail material are obtained. The contact characteristics variations versus separation, such as contact force, contact stiffness, and contact area, are shown in semilogarithmic diagrams considering different surface roughnesses and hardening parameters. The new model results show the significant influence of the assumed hypothesis on the contact characteristics.

Free-Form-Gear (FFG) is a recently published title for a gear that has a curved path of contact and offers contact between a convex addendum and a concave dedendum during the meshing cycle. Based on this method of designing a gear pair, the path of contact can be altered to improve the way the gears mesh and slide against each other by only adjusting the maximum pressure angle and the involute curve parameter. The analytical investigations into this gear pair indicated that, when compared to the standard involute gear pair, the sliding velocity, meshing efficiency, contact, and fillet strengths are improved while the contact ratio is decreased. In this study, experimental stress analysis is conducted on various configurations of the tooth profile and tooth fillet shape for the proposed FFG and the standard involute gear to validate the analytical results. Since it is difficult to measure the contact stress for the gear specimens, the contact stresses at critical points are estimated using an effective computational technique based on photoelastic data and a numerical approach utilizing the nonlinear least squares method. At the fillet zone, isochromatic fringe patterns are used to directly measure the maximum fillet stress. Using addendum modification coefficients, the reduction in contact ratio for the proposed FFG is eliminated, and the results are then verified experimentally. Based on the experimental estimations, the finite element analyses are conducted using ABAQUS to simulate the examined gear specimens. Under the same loading conditions, the experimental, analytical, and numerical results have all been in good agreement.