Interest For Aerospace Applications Research Articles

Design and workspace analysis of a cable-driven space capture robot for noncooperative targets

Capturing noncooperative targets in space has garnered continuous research interest in aerospace applications. This study addresses the demands of large-scale, multifaceted activities and varied working conditions for space capture missions by designing a space capture robot composed of multiple cable-driven manipulators operating in parallel. First, single- and multi-segment cable-driven robot models were designed, and a geometric model was subsequently built. The optimal number of segments was determined by analysing the condition number of a Jacobian matrix using the Monte Carlo method. Subsequently, based on the constant-curvature assumption, a kinematic model of the cable-driven space capture robot was formulated, and capture methods for different capture targets were designed using the Monte Carlo method. Finally, an eight-segment cable-driven robot prototype was developed, and compliance and driving experiments were conducted. This robot exhibits promising application potential for space noncooperative target capture and can be feasibly manufactured using on-orbit 3D machining technology.

Fabrication of flapping-wing micromechanism assembly using selective laser melting and aerodynamic performance measures

The development of a flapping wing microaerial vehicle mechanism with a high strength-to-weight ratio to withstand high flapping frequency is of significant interest in aerospace applications. The traditional manufacturing methods such as injection moulding and wire-cut electrical discharge machining suffer from high cost, labour intensiveness, and time-to-market. However, the present disruptive additive manufacturing technology is considered a viable replacement for manufacturing micromechanism components. Significantly to withstand high cyclic loads, metal-based high strength-to-weight ratio flapping wing microaerial vehicle components are the need of the hour. Hence, the present work focused on the fabrication of flapping wing microaerial vehicle micromechanism components using selective laser melting with AlSi10Mg alloy. The manufactured micromechanism components attained 99% of dimensional accuracy, and the total weight of the Evans mechanism assembly is 4 g. The scanning electron microscopy analysis revealed the laser melting surface characteristics of the Al alloy. The assembled mechanism is tested in static and dynamic environments to ensure structural rigidity. Aerodynamic forces are measured using a wind tunnel setup, and 7.5 lift and 1.2 N thrust forces are experienced that will be sufficient enough to carry a payload of 1 g camera on-board for surveillance missions. The study suggested that the metal additive manufacturing technology is a prominent solution to realize the micromechanism components effortlessly compared to conventional subtractive manufacturing.

Static test of a variable stiffness thermoplastic composite wingbox under shear, bending and torsion

AbstractAutomated manufacturing of thermoplastic composites has found increased interest in aerospace applications over the past three decades because of its great potential in low-cost, high rate, repeatable production of high performance composite structures. Experimental validation is a key element in the development of structures made using this emerging technology. In this work, a $750\times640\times240$ mm variable-stiffness unitised integrated-stiffener out-of-autoclave thermoplastic composite wingbox is tested for a combined shear-bending-torsion induced buckling load. The wingbox is manufactured by in-situ consolidation using a laser-assisted automated tape placement technique. It is made and tested as a demonstrator section located at 85% of the wing semi-span of a B-737/A320 sized aircraft. A bespoke in-house test rig and two aluminium dummy wingboxes are also designed and manufactured for testing the wingbox assembly which spans more than 3m. Prior to testing, the wingbox assembly and the test rig were analysed using a high fidelity finite element method to minimise the failure risk due to the applied load case. The experimental test results of the wingbox are also compared with the predictions made by a numerical study performed by nonlinear finite element analysis showing less than 5% difference in load-displacement behaviour and buckling load and full agreement in predicting the buckling mode shape.

Broadband Electromagnetic Absorbing Structures Made of Graphene/Glass-Fiber/Epoxy Composite

Radar-absorbing structures (RASs) with improved mechanical properties and subwavelength thickness are of particular interest for aerospace applications and electromagnetic (EM) interference control. This article proposes a new RAS, made of a graphene-filled lossy laminate (LL) with impedance adapter, having a total thickness less than 4 mm and a normalized absorption bandwidth of 84% in the frequency range 6–18 GHz. The RAS is designed by applying an innovative simulation approach of the graphene-filled LL, which is based on the multiscale Maxwell Garnett model and the effective medium theory. Experimental tests are performed in order to validate the developed model and to assess the absorption properties of the produced RAS, having a minimum reflection of −30 dB and an absorption bandwidth at −10 dB of 10 GHz, with a central frequency of 12 GHz and a graphene nanoplatelets concentration less than 5 g/m2.

Characterization of Phase Structures of Novel Metallo‐Polyurethanes

Two series of chemically well‐defined polyurethanes (PUs) have been synthesized containing two different soft segments of interest in aerospace applications. At a given soft fragment, four different hard segments (HSs) based on single diisocyanate molecules with no chain extenders have been incorporated. Both segmented PU series have been prepared by stoichiometric reactions of the macrodiol hydroxyl‐terminated polybutadiene (HTPB), and a metallo‐derived, this being the (ferrocenylbutyl) dimethylsilane grafted on HTPB, so‐called Butacene. Those HSs are isophorone diisocyanate, toluene‐2,4‐diisocyanate, 4,4′‐diphenyl methane diisocyanate, and hexamethylene diisocyanate. Microphase separation and morphology development have been studied at room temperature in these copolymers using Fourier transform infrared spectroscopy, analyzing the change in the relative intensities of free and hydrogen‐bonded carbonyl peaks. Measurements of wide‐ and small‐angle X‐ray diffraction using synchrotron radiation allow analyzing the morphological and microstructural differences between these two series of samples. In addition, dynamic mechanical analysis and differential scanning calorimetry have been used to learn about the relaxation processes and thermal transitions that are observed in these materials and to confirm the existence or lack of phase segregation. The knowledge of structure–property relationship is very important in these advanced organometallic PUs to get an understanding of their application as solid composite propellants binder. image

Enhanced thermal properties of phthalonitrile networks by cooperating phenyl-s-triazine moieties in backbones

The development of phthalonitrile resins is of particular interest for aerospace applications because of their excellent heat resistance. Here, heteroaromatic phenyl-s-triazine moieties have been introduced into the architecture of the phthalonitrile resin as thermally stable segments via a two-step, one-pot reaction. Bis(4-[4-aminophenoxy]phenyl)sulfone was selected to promote the curing reaction, and the gelation time could be readily controlled by the diamine concentration and the curing temperature as evidenced by rheometric measurements. The curing procedure was optimized to give high cross-linking density networks. The resulting networks exhibit high glass transition temperatures at around 400 °C, outstanding thermo-oxidative stability with weight retention of 95% ranging from 539 °C to 552 °C, suggesting an improvement of the thermal properties imposed by phenyl-s-triazine units. Additionally, the CF laminate of the resin possesses high flexural strength of 1722 MPa and interlaminar shear strength of 71 MPa at ambient temperature, and these values retain 255 MPa and 36 MPa at 450 °C, respectively.

Sensitivity of bistable laminates to uncertainties in material properties, geometry and environmental conditions

Under certain conditions asymmetric composite laminates can have a bistable response to mechanical loading. A transition between the two stable states provides opportunities to produce large deflections or shape changes from relatively low energy inputs that do not need to be maintained to sustain a specific shape. Such laminates are attracting interest in aerospace applications, deployable structures and energy harvesting. Accurate modelling predictions of bistable laminate shapes has proven challenging, in part due to uncertainties in geometry, material properties and the operating environment of the laminates. In this paper a detailed sensitivity analysis of the influence of each of these properties on laminate curvature is undertaken and demonstrates that bistable laminates are most sensitive to uncertainties in the Young’s moduli, thermal expansion coefficients, ply thickness and the temperature change from the elevated cure temperature. Accurate characterisation of these properties and quality control during manufacture can reduce the discrepancies between analytical models and experimental results and allow the models to be used as viable tools for the design of bistable laminates. It is also shown that laminates are highly sensitive to moisture absorption and temperature changes, especially when changes in material properties due to temperature were included in the modelling.

Nonequilibrium reaction rates in the macroscopic chemistry method for direct simulation Monte Carlo calculations

The direct simulation Monte Carlo (DSMC) method is used to simulate the flow of rarefied gases. In the macroscopic chemistry method (MCM) for DSMC, chemical reaction rates calculated from local macroscopic flow properties are enforced in each cell. Unlike the standard total collision energy (TCE) chemistry model for DSMC, the new method is not restricted to an Arrhenius form of the reaction rate coefficient, nor is it restricted to a collision cross section which yields a simple power-law viscosity. For reaction rates of interest in aerospace applications, chemically reacting collisions are generally infrequent events and, as such, local equilibrium conditions are established before a significant number of chemical reactions occur. Hence, the reaction rates which have been used in MCM have been calculated from the reaction rate data which are expected to be correct only for conditions of thermal equilibrium. Here we consider artificially high reaction rates so that the fraction of reacting collisions is not small and propose a simple method of estimating the rates of chemical reactions which can be used in the MCM in both equilibrium and nonequilibrium conditions. Two tests are presented: (1) The dissociation rates under conditions of thermal nonequilibrium are determined from a zero-dimensional Monte Carlo sampling procedure which simulates “intramodal” nonequilibrium; that is, equilibrium distributions in each of the translational, rotational, and vibrational modes but with different temperatures for each mode; (2) the 2D hypersonic flow of molecular oxygen over a vertical plate at Mach 30 is calculated. In both cases the new method produces results in close agreement with those given by the standard TCE model in the same highly nonequilibrium conditions. We conclude that the general method of estimating the nonequilibrium reaction rate is a simple means by which information contained within nonequilibrium distribution functions predicted by the DSMC method can be included in the macroscopic chemistry method.