Potential Aerospace Applications Research Articles

Review of Bearingless Synchronous Motors: Principle and Topology

A bearingless synchronous motor (BLSM) is a special type of electric machine that integrates the functions of traditional synchronous motors and magnetic bearings. It not only has the advantages of magnetic bearings, such as no friction, pollution-free, and maintenance-free, but it also realizes the high integration and system simplification. Therefore, the BLSM is becoming increasingly attractive in applications such as rotating stages, compressors, artificial hearts, and centrifugal pumps. This article provides a comprehensive review of the BLSM topologies after a brief introduction to the basic suspension force generation principles and the typical BLSM mathematical models. The recent BLSM topologies are classified based on the features of the suspension force generation principle. Moreover, the advantages and disadvantages of each BLSM type are discussed and compared in detail. Future potential BLSM applications in aircraft, aerospace, and flywheel energy storage systems are discussed after a short description of the BLSM application status. Several potential topology development directions are presented based on the requirements of the potential application.

Optic-fiber vector magnetic field sensor utilizing magneto-shape effect of magnetic fluid

In this work, an optic-fiber sensor utilizing magneto-shape effect of magnetic fluid (MF) has been put forward to measure magnetic field direction. MF magneto-shape effect has been presented, simulated and verified through experiments as a magneto-optical effect. The sensor consists of a capillary glass tube, two single-mode fibers (SMFs) and MF. The interface between MF and air is concave because the glass tube is attractive to MF. As magnetic field rises, the concavity degree becomes more obvious, in other words, edge length of MF cavity is extended and central length of cavity is shortened. The interference wavelength of sensor will change with magnetic field, so as to achieve the purpose of monitoring magnetic field. The phenomenon is defined as the magneto-shape effect of MF. Due to the magnetic field direction dependence of pressure difference between the MF and air, the magneto-shape effect of MF has different perception of axial magnetic field and radial magnetic field, realizing vector magnetic field measurement. Results of experiment are shown as follows: the sensor can easily react to field strength and orientation. The wavelength shows the shape of number “8″ with magnetic field direction changing. The field sensitivity reaches up to 296.1 pm/Gs from 22.6 Gs to 121.8 Gs in the axial field. Moreover, direction sensitivity reaches 311.6 pm/° at 104.4 Gs. The wavelength shift in the axial direction is 25.5 times higher than that of the radial direction. The presented sensing structure could monitor vector magnetic field without constructing a non-circular symmetrical structure. The proposed sensing structure is provided with characteristics of simple to make, highly-sensitive and little fabrication consumption. It possesses potential applications in electronic power industry and aerospace.

Lightweight auxetic metamaterials: Design and characteristic study

In the past decades, auxetic metamaterials have attracted extensive attention due to their desirable properties. In order to further improve the energy absorption properties of auxetic metamaterials, this work investigates the design of lightweight auxetic metamaterials based on the elliptic perforated plate. The material in the large deformation region is retained and the material in the small deformation region is removed as much as possible. The experimental and numerical results indicate that the mechanical properties of the novel metamaterials are almost unchanged, but the specific energy absorption is substantially enhanced owing to the reduced material overall and the distribution of the optimized materials to the most needed area. In this paper, the influence of the amount and mode of the material removal on the mechanical properties of the auxetic metamaterial is explored through the numerical method. The proposed auxetic metamaterials with lightweight characteristics have potential applications in many fields, e.g., civil engineering, aerospace and vehicle engineering.

In situ investigation of the healing process in dual-microcapsule self-healing materials by the synchrotron radiation computed tomography

Microcapsule-based self-healing materials have attracted overwhelming attention for their smart damage recovery capability with great potential applications in aerospace, electronic devices, etc. Numerous experimental and numerical methods have been developed to analyze the healing performance. However, there is a lack of understanding of the in-situ damaging and healing process under external loading. Here, an in-situ investigation on the internal three-dimensional microstructure evolution and damaging-healing process of a dual-microcapsule-based self-healing material with fast healing chemistry was performed by SR-CT technology. Some important but previously undiscovered phenomena such as microcapsules rupture, crack propagation, healing liquids flowing and mixing were clearly observed. Further study combined with 3-Dimensional stress field analysis indicates that the healing behaviors have significant regional characteristics, and were affected by multiple factors including the geometric, internal defects and especially the gradient distribution of stress field. These results may provide useful guidance for the design and performance optimization of self-healing materials.

3D Printing of Auxetic Metamaterials with High‐Temperature and Programmable Mechanical Properties

AbstractNegative Poisson's ratio mechanical metamaterials with typical auxetic behavior have great potential applications in aerospace and flexible electronics. However, the structure and properties of conventional mechanical metamaterials are fixed after fabrication, which greatly limit their applications. In recent years, some progress has been made in combining shape‐memory polymers (SMP) with 4D printing to develop auxetic metamaterials with programmable mechanical properties. Unfortunately the low‐temperature phase change of conventional SMP greatly hinders the further development of 4D printed mechanical metamaterials in the field of high‐temperature and high‐strength service. Here, the high‐performance polymer polyetheretherketone (PEEK) as the printing material is selected and a new mechanical metamaterial is prepared using fused deposition molding technology to program the material structure and properties by designing the structural parameters of the metamaterial mesh structure. In addition, thermal analysis shows that the printed samples have good thermal stability, including a phase change temperature of 170 °C, an initial thermal decomposition temperature greater than 500 °C, and qualified shape memory properties. Combining structural design with the shape memory properties of PEEK, reconfigurable metamaterial structure and properties are realized. Finally, 2D digital mesh structure is designed and fabricated with selective stretching strain positions and a stretchable circuit with constant resistance.

Thermal shock resistance enhancement by improved interfacial bonding for carbon/aluminium composites

Carbon/aluminium (C/Al) composites have the advantages of low density and high electrical conductivity, which have potential applications in aerospace, rail transportation and other fields. However, the unstable bonding of the C/Al interface and significant thermal expansion differences have resulted in risks of the composites' failure once suffering from severe thermal shock. In this work, the C/Al composites were prepared by the pressure impregnation method, and silicon (Si) was added to overcome the problems of C/Al non-wettability and thermal expansion differences. The effects of mass fractions of doped silicon on the mechanical properties, electrical conductivity and thermal shock resistance of C/Al composites were also examined. Results show that the formed SiC interlayer has effectively enhanced the interfacial bonding and reduced the differences in the thermal expansion coefficient of each component. As a result, the thermal shock resistance of the composites has been remarkably improved, and the flexural strength could remain 90% of the original level after the thermal shock test, compared with 50% of that without Si doping.

A Self-Stabilized Inverted Pendulum Made of Optically Responsive Liquid Crystal Elastomers.

The inverted pendulum system has great potential for various engineering applications, and its stabilization is challenging because of its unstable characteristic. The well-known Kapitza’s pendulum adopts the parametrically excited oscillation to stabilize itself, which generally requires a complex controller. In this paper, self-sustained oscillation is utilized to stabilize an inverted pendulum, which is made of a V-shaped, optically responsive liquid crystal elastomer (LCE) bar under steady illumination. Based on the well-established dynamic LCE model, a theoretical model of the LCE inverted pendulum is formulated, and numerical calculations show that it always develops into the unstable static state or the self-stabilized oscillation state. The mechanism of the self-stabilized oscillation originates from the reversal of the gravity moment of the inverted pendulum accompanied with its own movement. The critical condition for triggering self-stabilized oscillation is fully investigated, and the effects of the system parameters on the stability of the inverted pendulum are explored. The self-stabilized inverted pendulum does not need an additional controller and offers new designs of self-stabilized inverted pendulum systems for potential applications in robotics, military industry, aerospace, and other fields.

Additively manufactured AlSi10Mg ultrathin walls: Microstructure and nano-mechanical properties under different energy densities and interlayer cooling times

For additive manufacturing (AM) applications of lightweight aluminum alloy parts such as radiators, it is necessary to understand the relationship between internal microstructure and local mechanical properties. The microstructure characteristics and its formation mechanism of AlSi10Mg ultrathin walls fabricated by selective laser melting (SLM) under different energy densities and interlayer cooling times were investigated, and its evolution regularity with energy density was also analyzed. The nano-mechanical properties of different regions on the ultrathin-walled cross-section and their responses with energy density were also explored. The main results show that non-banding regions and banding regions distributed alternately like sandwiches are formed in ultrathin walls, which have fine solidified cellular structure and columnar dendrite network, accompanied by nano-scale substructure formed in grains. Although the microstructure characteristics and nano-mechanical properties of ultrathin walls are insensitive to interlayer cooling time, the single-track energy density significantly affects the coarsening of solidification structure and its substructure evolution. With the increase of single-track energy density, the interaction between various strengthening mechanisms related to the evolution of microstructure comprehensively affects the nano-hardness of different macro-areas in ultrathin walls, which follows the trend of increasing first and then decreasing, and higher nano-hardness can be obtained when the dimensionless single-track energy density is between 10 and 20. The findings of this work are beneficial to optimize the SLM process of AlSi10Mg alloy to manufacture ultrathin-walled parts with ideal microstructure and mechanical properties for potential applications in aerospace, automotive and other fields.

Compressive performance and fracture mechanism of bio-inspired heterogeneous glass sponge lattice structures manufactured by selective laser melting

High precision lattice structure (LS) shows great potential applications in aerospace, acoustic, biomedical, and wearable products due to its multifunctional characteristics and excellent mechanical properties. Inspired by lightweight, high-strength, and high-stability glass sponges (GSs), a unique circle-/grid-like heterogeneous glass sponge lattice structure (GSLS) was successfully designed and manufactured by selective laser melting (SLM) with Ti6Al4V alloy. Compared with the commonly used body-centred cubic (BCC), face-centred cubic (FCC), honeycomb and diamond LSs, GSLS displays the strongest compressive properties (E = 1560 MPa, σmax = 40 MPa, σy0.2 = 34 MPa, W = 5.95 J). The normalised elastic modulus and normalised compressive strength of GSLS are almost 1.4 and 1.3 times, 2.6 and 2.4 times, 2.7 and 3.5 times, 18 and 8.3 than that of FCC, BCC, honeycomb, and diamond LSs, respectively. Most importantly, unlike the 45° diagonal shear failure of homogeneous BCC and FCC, the FEA simulation reveals that the heterogeneous unit cell in GSLS can enhance the strut connectivity, disperse the stress, and exhibits a unique fracture mechanism of cell-after-cell and layer-by-layer. The fracture mechanism of GSLS can improve the load-bearing capability, maintain strength, and protect its interior and entire integrity during compression.

The Role of Tetra Hybrid Reinforcements on the Behavior of Aluminum Metal Matrix Composites

Hybrid aluminum matrix composites (HAMCs) are a new class of advanced materials that can be customized and engineered to achieve specific properties for specific applications in specific environments. HAMCs find a wide range of popularity in the transportation sector because of lower noise and lower fuel consumption over other materials. This research aims to synthesize, characterize, and test the physicomechanical characteristics of tetra hybrid (SiC, Al2O3, Gr, and sugarcane bagasse ash (SCBA)) reinforced HAMCs via powder metallurgy (PM) processing. Tetra hybrid reinforced HAMCs were synthesized using a pure Al matrix with fixed wt% of primary reinforcements (5 wt% SiC and 5 wt% Al2O3) and varying wt% of secondary reinforcements such as 0.5, 2.5, 4.5, and 6.5 wt% Gr and 0.5, 2.5, 4.5, and 6.5 wt% SCBA. It mainly focused on phase purity investigation using XRD, thermal analysis using TGA‐DTA, and surface area and micropore size analysis using BET and physicomechanical tests to explore the materials’ behavior of the newly synthesized HAMCs. The increase in wt% of secondary reinforcements decreases both the density and porosity while increasing the hardness and compressive strength up to a certain level above which it begins to reverse because of the increase in wt% of hard particles of SiC, Al2O3, and SCBA. The Vickers hardness and compressive strength of the AS4 HAMC with 10 wt% (SiC+Al2O3) and 9 wt% (Gr+SCBA) were improved by 446.40% and 209.75%, respectively. The newly synthesized tetra hybrid reinforced HAMCs showed superior physicomechanical properties compared to pure Al and single and double reinforced HAMCs. As a result, the new tetra hybrid reinforced HAMC material is predicted to have potential applications in automotive, aerospace, defense, and various other structural applications.

Multi-Terminal Nanotube Junctions: Modeling and Structure-Property Relationship

Carbon nanotube based multi-terminal junction configurations are of great interest because of the potential aerospace and electronic applications. Multi-terminal carbon nanotube junction has more than one carbon nanotube meeting at a point to create a 2D or 3D structure. Accurate atomistic models of such junctions are essential for characterizing their thermal, mechanical and electronic properties via computational studies. In this work, computational methodologies that uses innovative Computer-Aided Design (CAD) based optimization strategies and remeshing techniques are presented for generating such topologically reliable and accurate models of complex multi-terminal junctions (called 3-, 4-, and 6-junctions). This is followed by the prediction of structure-property relationship via study of thermal conductivity and mechanical strength using molecular dynamics simulations. We observed high degradation in the thermal and mechanical properties of the junctions compared to pristine structures which is attributed to high concentration of non-hexagonal defects in the junction. Junctions with fewer defects have better thermal transport capabilities and higher mechanical strengths, suggesting that controlling the number of defects can significantly improve inherent features of the nanostructures.

Wear and failure mechanisms of SiAlON ceramic tools during high-speed turning of nickel-based superalloys

Nickel-based superalloys have become one of the most promising and potential materials in gas turbine engine components contributing to aerospace industry due to their outstanding mechanical properties (high ductility, high temperate strength, etc.). However, the poor machinability (lower thermal conductivity, high work hardening, etc.) and low machining efficiency of nickel-based superalloys have further hampered it to be widely applied in the potential aerospace applications. In this work, we systematically investigated the effects of various cutting speeds (i.e. 100–400 m/min) on tool wear and failure mechanisms of the SiAlON ceramic tools in the dry cutting of nickel-based superalloys by performing high-speed turning experiments. The tool life and wear evolution with the cutting distance at various cutting speeds were studied; the response relationship of tool flank wear, cutting speed, and cutting distance was visually presented. The optimal cutting speed range could be 200 m/min∼300 m/min in our cutting conditions considering the tool life and the response relationship. Further, tool wear and failure mechanisms are demonstrated to be the adhesion, catastrophic fracture, and microcracks at flank wear land; and the micro-chipping is observed at rake face at a low cutting speed of 100 m/min. Additionally, at a higher cutting speed of 400 m/min, the wear and failure mechanisms are severe adhesion, cutting edge micro-chipping, microcracks, but none of catastrophic fracture failure. This disparity can be attributed to the different alternating dominant effects in strain hardening and thermal softening mechanisms behind the machining process.

Dynamic Nanoconfinement Enabled Highly Stretchable and Supratough Polymeric Materials with Desirable Healability and Biocompatibility.

Lightweight polymeric materials are highly attractive platforms for many potential industrial applications in aerospace, soft robots, and biological engineering fields. For these real-world applications, it is vital for them to exhibit a desirable combination of great toughness, large ductility, and high strength together with desired healability and biocompatibility. However, existing material design strategies usually fail to achieve such a performance portfolio owing to their different and even mutually exclusive governing mechanisms. To overcome these hurdles, herein, for the first time a dynamic hydrogen-bonded nanoconfinement concept is proposed, and the design of highly stretchable and supratough biocompatible poly(vinyl alcohol) (PVA) with well-dispersed dynamic nanoconfinement phases induced by hydrogen-bond (H-bond) crosslinking is demonstrated. Because of H-bond crosslinking and dynamic nanoconfinement, the as-prepared PVA nanocomposite film exhibits a world-record toughness of 425± 31MJ m-3 in combination with a tensile strength of 98MPa and a large break strain of 550%, representing the best of its kind and even outperforming most natural and artificial materials. In addition, the final polymer exhibits a good self-healing ability and biocompatibility. This work affords new opportunities for creating mechanically robust, healable, and biocompatible polymeric materials, which hold great promise for applications, such as soft robots and artificial ligaments.

Random decision forest based sustainable green machining using Citrullus lanatus extract as bio-cutting fluid

The presently employed synthetic cutting fluids in machining applications lead to skin irritations, hazardous aerosols, ingestion etc., to the machine tool operators. Accomplishing sustainable green machining through bio-cutting fluids, is the key motivating factor behind this work, even though the phenomenon of heat generation is inevitable in the machining process. In the present investigation, Citrullus lanatus extract is chosen as a potential candidate for bio-cutting fluid, since it offers multiple benefits such as increased tool life, cleaner production atmosphere, efficacious heat dissipation, healthy operating conditions, etc. Hybrid LM0-6SiCp-4Grp composite is selected for study since; it has potential applications in marine, aerospace, defence and automotive sectors. Experimentation is carried out with Citrullus lanatus extract as bio-cutting fluid in turning of hybrid LM0-6SiCp-4Grp composite under different processing conditions. The presence of green solution based on Citrullus lanatus extract curtails the rise of temperature significantly during turning operation. Higher magnitude of temperature decrease is observed when the percentage of the concentration of Citrullus lanatus extract is increased, irrespective of depth of turning. Bio-nature and cooling qualities of this green-cutting fluid can contribute its share for green machining and sustainable turning environment. The investigations are further progressed using machine learning algorithms based on the different categories of logical regressions implemented through the Python program. Random forest regression shows better results with 99.8% prediction accuracy compared to other machine learning approaches and the decision tree is constructed through the respective regression model. Decision tree has the ability to handle process parameters systematically and predicts the implications of Citrullus lanatus extract in decreasing the temperature at machine-tool interface during machining operation. This tree structured analysis provides a better inference that delivers flexibility in turning parameters and opens up wider options for operation. Thus, decision tree approach ensures optimized usage of production resources and increases the production capacity through judicial selection of cooling approaches associated with the turning process.

Fabrication of highly flexible electromagnetic interference shielding polyimide carbon black composite using hot-pressing method

Traditionally, electromagnetic interference (EMI) shielding material has been occupied by metallic materials due to its high electric conductivity and EMI shielding effect. However, with rising demands from technology development for light-weight, highly durable, and easily moldable materials, metallic materials are gradually being substituted by polymer composite materials. Still, there are limitations on polymer composite as EMI shields: High ratio of fillers in composite achieves excellent EMI shielding effect but it severely compromises its mechanical behaviors. In many studies, they have failed to fabricate the high-ratio filler films with good mechanical durability, but here the initially fragile high-ratio film has been transformed to a flexible film by a very simple method: Hot-pressing. This approach not only solved the problems mentioned above but further provided a possible breakthrough point for composite study by solving threshold of the maximum loading of the fillers in polymer matrix. The stiff composite of polyimide sponge with exceeding carbon black loading became a highly flexible EMI SE film with doubled tensile strength and enhanced EMI SE. As a result, a new way of fabricating flexible EMI shielding polymer composite is demonstrated with great potential applications in aerospace and wireless communications.

Photosensitive Composite Inks for Digital Light Processing Four-Dimensional Printing of Shape Memory Capture Devices.

High-performance shape memory thermosetting polymers and their composites for four-dimensional (4D) printing are essential in practical applications. To date, most printable thermosets suffer from complicated processes, poor thermodynamic performances, and low printing speed. Here, photosensitive composite inks for fast photocuring printing are developed. The inks consist of epoxy acrylate (EPAc), polyethylene glycol dimethacrylate (PEGDMA), and carbon fillers, which form a firm network structure when exposed to UV light. EPAc is synthesized via addition esterification of epoxy resin and acrylic acid under mild conditions. It is worth noting that raw materials for the reaction are diverse, including not only various epoxy resins but also molecules with epoxy groups. The 4D printing speed of up to 180 mm/h is mainly attributed to the exothermic reaction initiated by free radicals, which accelerates the polymerization of EPAc and PEGDMA. Most importantly, by increasing the exposure time of each layer from 1 s to 3 s during the printing process, the epoxy composite-infilled carbon nanotubes and carbon fibers are printed to ensure the integrity of the microlayer structure. Furthermore, we design a claw-like catcher device based on the above printable composite inks to demonstrate its potential applications in aerospace, such as grasping end-of-service spacecraft or explosive debris. Undoubtedly, 4D printing technology opens up a new portal for the manufacturing of thermoset epoxy composites and complex structures, which make the shape memory thermosetting epoxy resins and their composites possess excellent properties and good engineering application prospects.

A Comprehensive Review on Optimal Welding Conditions for Friction Stir Welding of Thermoplastic Polymers and Their Composites.

Friction stir welding (FSW) and friction stir spot welding (FSSW) techniques are becoming widely popular joining techniques because of their increasing potential applications in automotive, aerospace, and other structural industries. These techniques have not only successfully joined similar and dissimilar metal and polymer parts but have also successfully developed polymer-metallic hybrid joints. This study classifies the literature available on the FSW and FSSW of thermoplastic polymers and polymer composites on the basis of joining materials (similar or dissimilar), joint configurations, tooling conditions, medium conditions, and study types. It provides a state-of-the-art and detailed review of the experimental studies available on the FSW and FSSW between similar thermoplastics. The mechanical properties of FSW (butt- and lap-joint configurations) and FSSW weld joints depend on various factors. These factors include the welding process parameters (tool rotational speed, tool traverse speed, tool tilt angle, etc.), base material, tool geometry (pin and shoulder size, pin profile, etc.) and tool material, and medium conditions (submerged, non-submerged, heat-assisted tooling, cooling-assisted tooling). Because of the dependence on many factors, it is difficult to optimize the welding conditions to obtain a high-quality weld joint with superior mechanical properties. The general guidelines are established by reviewing the available literature. These guidelines, if followed, will help to achieve high-quality weld joints with least defects and superior mechanical properties. Apart from parametric-based studies, the statistical-based studies (e.g., analysis of variance (ANOVA)-based studies) are covered, which helps with the determination of the influential parameters that affect the FSW and FSSW weld joint strength. Also, the optimal ranges of the most influential process parameters for different thermoplastic materials are established. The current work on the development of general guidelines and determination of influential parameters and their operating ranges from published literature can help with designing smart future experimental studies for obtaining the global optimum welding conditions. The gaps in the available literature and recommendations for future studies are also discussed.

Facile synthesis of bio-based tetra-functional epoxy resin and its potential application as high-performance composite resin matrix

In order to meet the increasing performance demands for resin matrix in aerospace industry and fulfill the sustainable development strategy, designment of bio-based epoxy resins with satisfactory comprehensive properties outperforming N,N,N′,N′-tetraglycidyl-4,4′-diaminodipehnylmethane (TGDDM) for high-end application is of paramount important but also a formidable challenge. Herein, a simple and high-efficient method was proposed to synthesize a bio-based tetra-functional epoxy resin (MTEP) from a sustainable biomass feedstock, magnolol. With 4,4′-diaminodiphenyl sulfone (DDS) as curing agent, the cured MTEP/DDS showed a record glass transition temperature of 326 °C and an ultrahigh char yield of 52.1%, which was 83 °C and 1.1 times higher than those of TGDDM/DDS, respectively. In addition, the cured MTEP/DDS also exhibited a high flexural modulus of 3991 MPa and storage modulus (at 25 °C) of 3705 MPa, which were all superior to those of TGDDM/DDS. More impressively, thanks to the unique structure of magnolol, the cured MTEP/DDS illustrated lower water absorption in comparison with TGDDM/DDS, and possessed outstanding intrinsic flame retardancy, attaining V-0 rating in UL-94 test. This work adds new members to the synthetic toolbox of high-performance bio-based polymers as composite resin matrix for potential aerospace applications.

Preparation of a modified phosphate-based adhesive and its hot bonding performance on 316L stainless steel

In this study, a novel phosphate-based adhesive was prepared by using homemade aluminum phosphate as a matrix and by adding different fillers simultaneously. The effects of calcination temperature and filler composition on the bonding mechanism and high-temperature bonding strength of the adhesive for high-temperature alloys were studied. The results indicated that the crystalline transformation of AlPO4 occurred at 500 °C. AlPO4 has two crystalline forms at 500 °C: orthorhombic and hexagonal. The addition of CuO to the fillers resulted in the exchange of Fe and Cu at the substrate interface and enhanced the high-temperature bonding strength of the specimens. The maximum tensile strength of the specimens reached 3.9 MPa at 500 °C. These composites have potential applications in aviation, aerospace, and other fields.

Titanium Matrix Composites: Multiscale Architecture and Superior High‐Temperature Performance of Discontinuously Reinforced Titanium Matrix Composites (Adv. Mater. 6/2021)

In article number 2000688, Lujun Huang, Lin Geng, and co-workers comprehensively review the smart multiscale architecture and superior performance of titanium matrix composites. Multiscale discontinuously reinforced titanium matrix composites inspire coordinated strengthening mechanisms at different scales. This design method gives rise to lightweight materials with high strength, good ductility, and high-temperature durability, which have great potential in aerospace applications.