Potential Aerospace Applications Research Articles

Stability‐Enhanced Variable Stiffness Metamaterial with Controllable Force‐Transferring Path

AbstractSelf‐contact variable stiffness (SVS) metamaterial offers specific patterns of elastic strain energy storage by changing its force‐transferring path. The change of the elastic strain energy storage patterns further influences the stiffness variation of the SVS metamaterials. However, challenges still arise because typically fabricated SVS metamaterials inevitably contain structural irregularities, eccentricities, and defects. These microstructural imperfections impede the stable generation of designed strain energy storage patterns in the metamaterial, implying that the SVS metamaterials cannot achieve expected stiffness variations. To address this burning question, an SVS metamaterial/meta‐structure design paradigm with eccentric unit designs is proposed, which can realize both stable stiffness variations and high load‐bearing. The theoretical, simulation, and experimental results demonstrate that the SVS chain meta‐structure achieves ≈110 times stiffness variation between the low and high loading conditions. Its load‐bearing can reach more than 1500 N when the meta‐structure falls into the high stiffness stage. Furthermore, some typical functions are demonstrated using the stability‐enhanced SVS metamaterial, including customized mechanical protections for human joints and information transformation regulated by remote mechanical input signals. The results can provide a useful solution for generating a more feasible stability‐enhanced SVS metamaterial/meta‐structure and promote their potential applications in aerospace, medical devices, and robotics.

Study of Self-Locking Structure Based on Surface Microstructure of Dung Beetle Leg Joint.

Dung beetle leg joints exhibit a remarkable capacity to support substantial loads, which is a capability significantly influenced by their surface microstructure. The exploration of biomimetic designs inspired by the surface microstructure of these joints holds potential for the development of efficient self-locking structures. However, there is a notable absence of research focused on the surface microstructure of dung beetle leg joints. In this study, we investigated the structural characteristics of the surface microstructures present in dung beetle leg joints, identifying the presence of fish-scale-like, brush-like, and spike-like microstructures on the tibia and femur. Utilizing these surface microstructural characteristics, we designed a self-locking structure that successfully demonstrated functionality in both the rotational direction of the structure and self-locking in the reverse direction. At a temperature of 20 °C, the biomimetic closure featuring a self-locking mechanism was capable of generating a self-locking force of 18 N. The bionic intelligent joint, characterized by its unique surface microstructure, presents significant potential applications in aerospace and various engineering domains, particularly as a critical component in folding mechanisms. This research offers innovative design concepts for folding mechanisms, such as those utilized in satellite solar panels and solar panels for asteroid probes.

Computer-aided design of thermosetting benzoxazoles containing bis-endoalkynyl groups: Low melting points and high thermal stability

High-temperature-resistant polybenzoxazoles (PBOs) have recently become a prominent research area due to their potential applications in aviation and aerospace. However, achieving a balance between thermal stability and processability remains a significant challenge. In this study, a computer-aided method to develop PBOs with high thermal stability and processability is explored. First, thermoset benzoxazoles (CPBOs) are designed using a material genomic approach. Subsequently, their zero shear viscosity, temperature at 50 % thermal weight loss, dielectric constant and dielectric loss are predicted using a computer-aided method. Finally, two screened thermosetting benzoxazoles, CPBO-1 and CPBO-6, are synthesized and experimentally validated. The experiments indicate that their melting points are below 100 °C, with the lowest melt viscosities being 0.5 Pa•s and 1.5 Pa•s, respectively. The corresponding polymers, pCPBO-1 and pCPBO-6, feature high thermal stability. The 5 % weight loss temperature of pCPBO-1 in N2 is 618.9 °C, while the dielectric constant and dielectric loss are 3.1 and 0.0063, respectively. These are excellent values for thermosetting resins. This computer-aided screening method is more efficient and cost-effective compared to conventional trial-and-error methods.

Titanium surface functionalization via directed energy deposition of CuNiTi ternary alloy

Pure titanium is a soft material that tends to degrade quickly during service due to wear and microbiologically influenced corrosion. Therefore, current research aims at the deposition, microstructural characterization, and surface functionalization of the TiCuNi coatings on pure titanium substrate to improve its surface properties. Cu–Ni premixed elemental powders are deposited on the pure Ti by laser-directed energy deposition (LDED) using a novel method of extracting Ti from the substrate through melt pool convection. The single-track deposit geometry and integrity characterization using dilution percentage, heat-affected zone width (HAZ), and microhardness values show the sound metallurgical bonding with the substrate. The X-ray diffraction (XRD) pattern and microstructure image reveal the presence of NiTi binary (B2) and Ti2CuNi ternary (B19) hard phases and equiaxed dendritic morphology, respectively, demonstrating ternary alloy coating formation. The microhardness value of the coatings is thrice that of the substrate due to the presence of hard NiTi (B2) binary and Ti2CuNi (B19) ternary phases. The coating’s wear resistance is significantly (80%) higher than the substrate, owing to hard phases and Cu as a solid lubricant. The wear track consists of small grooves, adhered debris, and a smooth profile, mainly due to a significant reduction in adhesion and abrasion compared to the substrate. Moreover, the polarisation corrosion potential and current density are increased and decreased by 53% and 97%, respectively, displaying symbolic improvement in the corrosion resistance. Hence, this work has presented the LDED ability to enhance the pure Ti anti-wear and corrosion resistance properties by depositing CuNiTi ternary alloy coating for potential aerospace, marine, and biomedical applications.

Enhancing moisture-resistance in polyimide aerogels: A novel hydrophobic modification approach with ortho-positioned long-chain barriers

Polyimide (PI) aerogels possess significant potential for various applications due to their outstanding mechanics and thermal insulation. However, a major drawback of these aerogels is their susceptibility to moisture, which not only compromises their insulative performance but also leads to an increase in weight. To address this issue, we have developed a moisture-resistance technique by incorporating a long-chain hydrophobic barrier at the ortho position relative to the imide groups to enhance the moisture-resistance of the PI aerogels. This approach involved using a series of diamines with hydroxyl groups strategically located at the ortho position of imide groups as reactants. The resulting PI aerogels demonstrated a significant improvement in water resistance, reducing water-uptake to merely one-tenth of that recorded in unmodified samples. Furthermore, the effectiveness of this hydrophobic modification was validated through molecular dynamics simulations, which indicated a diffusion coefficient of 4.41 × 10−11 m2/s after modification. These findings represent a considerable advancement in developing effective methods for hydrophobic modification of PI aerogels, with potential applications in aerospace, electronic communications, and environmental protection.

Experimental and theoretical studies on 3D printed short and continuous carbon fiber hybrid reinforced composites

3D-printed carbon fiber composites hold significant potential in aerospace applications because of their lightweight, high strength and complex structure fabrication capabilities. However, additive manufacturing characteristics such as high porosity, anisotropy and continuous fiber content significantly affect the mechanical properties of printed parts. The aim of this study is to investigate the influence of hybrid printing of short and continuous carbon fibers on the mechanical properties and failure mechanisms of composites and to develop a model to predict elastic properties considering porosity. First, mechanical testing and characterization of short and continuous fiber reinforced polyamide (nylon) print filaments are performed. The results indicate that the elastic modulus and ultimate strength of continuous carbon fiber filaments reach 60 GPa and 1500 MPa, respectively, while the strength and elastic modulus of short carbon fiber filaments reach 60 MPa and 1 GPa, respectively. Then tensile specimens with different continuous fiber orientations and different continuous fiber placement sequences are printed and tested using a multi-material 3D printing technique. The specimens are characterized before and after testing using scanning electron microscopy and microscopy to assess the porosity and failure mechanisms of specimens with different configurations. The results show that the mechanical properties of the printed parts are much lower than those of the print filaments, which proves the serious negative impact of the material extrusion process on the mechanical properties of the printed structural parts. Finally, an analytical method for predicting the elastic behavior of printed composites is developed by introducing the porosity factor in the volume-averaged stiffness model. For continuous and short fiber filled composites with different fiber contents and printing orientations, the predicted results are in agreement with the experiments, and the prediction error is greatly reduced from 30 % to <5 %.

Production and development of ZnAlGeO semiconducting materials for thermoelectric generators in potential aerospace applications

Production and development of ZnAlGeO semiconducting materials for thermoelectric generators in potential aerospace applications

Production of ZnAlO semiconducting materials for thermoelectric generators in potential aerospace applications

Production of ZnAlO semiconducting materials for thermoelectric generators in potential aerospace applications

Dual-control of incubation effect for efficiently fabricating surface structures in fused silica

Abstract Fused silica with surface structures has potential applications in microfluidic, aerospace and other fields. To fabricate structures with high dimensional accuracy and surface quality is of paramount importance. However, it is indeed a challenge to strike a balance between accuracy and efficiency at the same time. Here, a temporally shaped femtosecond laser Bessel-beam-assisted etching method with dual-control of incubation effect is proposed to achieve this balance. Instead of layer-by-layer ablation continuously with Gaussian pulses, silica is modified discretely by double pulse Bessel beam with one single layer. During the modification process, incubation effect is dual-controlled in single shot process and spatial scanning process to generate even modified region efficiently. Then, the modified region is etched to form designed structures such as microholes, grooves, etc. The proposed method exhibits high efficiency for fabrication of surface structures in fused silica.

A systematic review of the process parameters, mechanical characteristics and applications of polyether ether ketone (PEEK) and its composites by additive manufacturing

Abstract Additive manufacturing (AM) provides an innovative and reliable method of developing medical products with anatomically relevant geometry and mechanical performance, underscoring its significant potential in the medical field. The design of fused deposition modelling (FDM) parameters has a significant impact on the characteristics of the product fabricated utilizing FDM. Numerous studies have assessed the impact of various FDM process parameters on enhancing the print quality attributes of manufactured components, such as mechanical characteristics, production times, dimensional accuracy, and surface finish. Because of the complex features of the FDM process and the contradicting process parameters, the advancement has been slow and poorly coordinated. This work intends to provide a complete review of recent research on PEEK and CF-PEEK printed parts, where the effect of process factors on tensile strength has been described. Furthermore, PEEK, with its potential applications in medical, aerospace, and chemical sectors, serves as an inspiring material for future innovations, offering a promising outlook.

Micromechanical response of graphene coating on nt-TiAl under nanoindentation

The nanoindentation response of graphene (Gr) coating on nanotwin titanium-aluminum (nt-TiAl) matrix composites was studied using molecular dynamics (MD) simulation. The indentation velocity, twin boundary spacing, and parallel and vertical Z-axes are studied. The results show that the bearing capacity and hardness of Gr coating is significantly higher than that after coating failure, and the load-displacement curve shows the same phenomenon. Damage to the substrate material at varying speeds is indicated by atomic aggregation near the Gr coating, with the center of aggregation showing a negative correlation with indentation velocity. The matrix's damaged area is larger when the twin layer is perpendicular to the Z-axis and deeper when parallel, showing that the twin structure limits material damage by hindering dislocation expansion. Moreover, the presence of Gr coating delayed the matrix's plastic deformation process. This delay effect significantly improves the mechanical properties of composites, which have potential applications in aerospace.

Dispersion Analysis of Plane Wave Propagation in Lattice-Based Mechanical Metamaterial for Vibration Suppression

Phononic crystals based on lattice structures provide important wave dispersion characteristics as band structures, showing excellent compatibility with additive manufacturing. Although the lattice structures have shown the potential for vibration suppression, a design guideline to control the frequency range of the bandgap has not been well established. This paper studies the dispersion characteristics of plane wave propagation in lattice-based mechanical metamaterials to realize effective vibration suppression for potential aerospace applications. Triangular and hexagonal periodic lattice structures are mainly studied in this paper. The influence of different geometric parameters on the bandgap characteristics is investigated. A finite element approach with Floquet–Bloch’s principles is implemented to effectively evaluate the dispersion characteristics of waves in lattice structures, which is validated numerically and experimentally with a 3D-printed lattice plate. Based on numerical studies with the developed analysis framework, the influences of the geometric parameters of lattice plate structures on dispersion characteristics can mainly be categorized into three patterns: change in specific branches related to in-plane or out-of-plane vibrations, upward/downward shift in frequency range, and drastic change in dispersion characteristics. The results obtained from the study provide insight into the design of band structures to realize vibration suppression at specific frequencies for engineering applications.

Active control vibrations of aircraft wings under dynamic loading: Introducing PSO-GWO algorithm to predict dynamical information

This study presents an innovative approach to mitigate vibrations induced by external shock on composite structures through the application of an intelligent controller. Leveraging the first-order shear deformation panel theory, a sophisticated controller scheme is developed, integrating methodologies such as the differential quadrature approach and Laplace transform. Furthermore, deep neural network (DNN) and support vector regression (SVR) techniques are employed to enhance prediction accuracy and control efficiency. Additionally, two optimized hybrid models are proposed, incorporating Particle Swarm Optimization (PSO) and Grey Wolf Optimizer (GWO) algorithms, to further refine the controller's performance. The proposed methodology aims to address the challenges associated with vibrations in composite structures by providing a comprehensive and adaptive control solution. By utilizing advanced optimization algorithms and machine learning techniques, the controller can effectively adapt to dynamic changes in external shock conditions, thereby minimizing vibrations and ensuring structural integrity. The integration of ANN and SVR enhances the controller's predictive capabilities, enabling it to anticipate and respond to varying shock scenarios with precision. Through theoretical analysis and numerical simulations, the effectiveness of the proposed intelligent controller is demonstrated in reducing vibrations and enhancing the structural stability of composite systems. The optimized hybrid models, employing PSO and GWO algorithms, further improve the controller's performance by fine-tuning its parameters for optimal control efficiency. Overall, this research contributes to the development of robust control strategies for mitigating vibrations in composite structures subjected to external shock, with potential applications in aerospace, automotive, and civil engineering industries.

3D printed auxetic metamaterials with tunable mechanical properties and morphological fitting abilities

Research on creating special structures with a negative Poisson’s ratio, known as auxetic metamaterials, is widely conducted for potential applications in flexible electronics, aerospace, biomedicine, and other fields. Auxiticity is the phenomenon of transverse expansion that occurs when stretched longitudinally. However, conventional metamaterial tunable properties have certain limitations, mainly in the form of limited Poisson’s ratio tuning range and transverse deformation. In this work, a series of symmetric antichiral auxetic structures with significant auxetic effect and low Poisson’s ratio of −5 are designed and fabricated by 3D printing. Based on the manipulating of unit parameters and the use of shape memory polymers, the auxetic metamaterials exhibit tunable mechanical properties and programmable shape memory behaviors. Owing to these features, the auxetic metamaterials are demonstrated to achieve excellent shape-fitting and size-fitting capabilities, which are followed by expanding in a full range to contact any objects (due to auxiticity) and then contract to conform their shapes (due to shape memory). By integrating flexible electromyography(EMG) electrodes, the shape memory auxetic metamaterials can be used as self-adaptive wearable devices to fit with human limbs, which can ensure the good attachment, high signal to Noise Ratio (SNR), and breathability when collect EMG signals.

Interplay of heat treatment and deformation temperature on the microstructural evolution and mechanical behavior of SLM AlSi10Mg alloy

This study conducts a comprehensive examination of the microstructural and dislocation dynamics of AlSi10Mg alloys under various thermal conditions, utilizing quasi in-situ Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM) analyses. The research focuses on comparing the microstructural response of as-built and T6 heat-treated samples to mechanical stress at both ambient (298 K) and cryogenic (77 K) temperatures. EBSD analysis underscores the grain stability under applied strain, while TEM investigations expose notable variations in dislocation mobility influenced by temperature, with a particular emphasis on the interaction between dislocations and silicon particles at cryogenic temperatures. An observed increase in Geometrically Necessary Dislocation (GND) density at 77 K points to enhanced resistance to plastic deformation, suggesting mechanisms of cryogenic strengthening. The findings illuminate the impact of heat treatment in augmenting the mechanical properties of the alloy, shedding light on its potential applications in aerospace and cryogenic environments.

Fabrication of high strength-ductility aluminum alloy heterogeneous plates using additive manufacturing and hot rolling process

Aluminum alloy heterogeneous plate has great potential applications in automotive, military, aerospace, and other fields due to its excellent mechanical properties and ability to resist ballistic missile penetration. In the present work, a 5356/7A48 aluminum alloy heterogeneous plate with high strength-ductility and excellent interfacial metallurgical bonding strength was prepared using wire-arc additive manufacturing and hot rolling (WAAM+HR) process. The yield strength and ultimate tensile strength were 280.2 MPa and 392.3 MPa, respectively, both of which were between 5356 and 7A48 alloys, but the elongation was excellent, up to 22%. Its excellent comprehensive mechanical properties far exceed those of Al/Al heterogeneous plates reported in previous studies. In addition, compared with traditional clad plates, its fracture displacement is improved by 48.8%, showing remarkably high interlayer bonding strength. The soft layer 5356 and the hard layer 7A48 beared the main plastic strain and normal stress respectively, resulting in back-stress strengthening at the interlayer interface, which was the fundamental reason for the synergistic effect of strength and plasticity. Furthermore, even at the maximum bending angle of 180°, the heterogeneous plate did not show any sign of fracture, thanks to the fact that the outer soft-clad layer accommodated most of the bending deformation. The heterogeneous lamella structure, high constraint of hard layer to soft layer, and high geometrically necessary dislocations (GNDs) density of interfaces effectively stimulated the back stress strengthening and dislocation hardening, so that the 5356/7A48 aluminum alloy heterogeneous plate exhibited excellent comprehensive mechanical properties. The proposed WAAM+HR process provides an approach for the preparation of multi-functional heterogeneous plates with high strength-ductility and superior bonding strength.

Gradients of properties increase the morphing and stiffening performance of bioinspired synthetic fin rays

State-of-the-art morphing materials are either very compliant to achieve large shape changes (flexible metamaterials, compliant mechanisms, hydrogels), or very stiff but with infinitesimal changes in shape that require large actuation forces (metallic or composite panels with piezoelectric actuation). Morphing efficiency and structural stiffness are therefore mutually exclusive properties in current engineering morphing materials, which limits the range of their applicability. Interestingly, natural fish fins do not contain muscles, yet they can morph to large amplitudes with minimal muscular actuation forces from the base while producing large hydrodynamic forces without collapsing. This sophisticated mechanical response has already inspired several synthetic fin rays with various applications. However, most ‘synthetic’ fin rays have only considered uniform properties and structures along the rays while in natural fin rays, gradients of properties are prominent. In this study, we designed, modeled, fabricated and tested synthetic fin rays with bioinspired gradients of properties. The rays were composed of two hemitrichs made of a stiff polymer, joined by a much softer core region made of elastomeric ligaments. Using combinations of experiments and nonlinear mechanical models, we found that gradients in both the core region and hemitrichs can increase the morphing and stiffening response of individual rays. Introducing a positive gradient of ligament density in the core region (the density of ligament increases towards the tip of the ray) decreased the actuation force required for morphing and increased overall flexural stiffness. Introducing a gradient of property in the hemitrichs, by tapering them, produced morphing deformations that were distributed over long distances along the length of the ray. These new insights on the interplay between material architecture and properties in nonlinear regimes of deformation can improve the designs of morphing structures that combine high morphing efficiency and high stiffness from external forces, with potential applications in aerospace or robotics.

Enhanced radiation hardness of lead halide perovskite absorber materials via incorporation of Dy2+ cations

Continuously growing evidence of the excellent radiation hardness of perovskite solar cells stimulates their intense exploration in the context of potential aerospace applications. However, there is still a very limited understanding of the fundamental aspects such as the mechanisms of the interaction of complex lead halides with different types of ionizing radiation and associated aging pathways, even though this knowledge is essentially important for the development of new materials with improved properties. Herein, we made one of the first steps to fill this gap through a systematic study of the aging behavior of two perovskite absorber materials under exposure to three different stressors: 60Co gamma-rays, 8.5 MeV electron fluences, and light. The application of a set of complementary spectroscopy and microscopy techniques allowed us to identify and compare perovskite degradation pathways caused by each type of the ionizing radiation. In particular, radiation-induced phase segregation with the formation of δ-phases of CsPbI3 and FAPbI3 appears to be a common route in the case of double cation perovskites. Most importantly, we have revealed that the incorporation of dysprosium cations as a replacement of 1 % of Pb2+ ions in the Cs0.12FA0.88Pb0.99Dy0.01I3 material formulation results in a remarkably improved radiation hardness: this modification blocks the formation of metallic lead and strongly suppresses segregation of Cs-rich and FA-rich phases in perovskite films under exposure to gamma rays or high-energy electrons. Thus, these results open up a promising research direction for designing radiation-resistant perovskite absorbers through rational compositional engineering.

Microstructure Evolution and Mechanical Properties of Ti–6Al–4Zr–4Nb Alloys Fabricated by Spark Plasma Sintering (SPS)

The near-α Ti–6Al–4Zr–4Nb (wt pct) alloy is a recently developed alloy with potential for aerospace applications. This study evaluates the microstructure and mechanical properties of Ti–6Al–4Zr–4Nb produced by spark plasma sintering (SPS). The SPS samples sintered in the α + β regions exhibited equiaxed α with a neighboring thin β phase. Above the β-transus temperature, the α/β lamellar structure formed, allowing control of the grain size (100 ~ 200 μm). The compressive strength and the creep property of the SPS samples were compared with the LBPDed and the forged samples. The compressive strength of the SPS sample was lower than that of the LPBFed sample but similar to the forged sample. The SPS samples exhibited longer creep rupture life (2220 hours) than LPBFed samples (1730 hours), but shorter than the forged sample (4109 hours). The creep deformation mechanism of the lamellar structure in the SPS sample was dislocation creep.

Superior Heat and Mass Transfer Performance of Bionic Wick with Finger-like Pores Inspired by the Stomatal Array of Natural Leaf.

The thermal management of electronics has gained significant attention, with loop heat pipes (LHPs) emerging as an attractive solution for heat dissipation. The heat transfer performance of LHPs is influenced by the heat and mass transfer processes within the wick. However, designing the pore diameter of the wick is challenging due to the different requirements of flow resistance and capillary force. Specifically, the working fluid needs large pores to reduce resistance, while the liquid suction requires small pores to provide a large capillary force. To address this issue, we drew inspiration from the stomatal array of natural leaves used for transpiration and developed an alumina ceramic bionic wick with finger-like pores using the phase-inversion tape casting method. The finger-like pores in the wick resemble the straight hole structure of stomata, which increases the gas-liquid interface area within the wick. This design allows for timely discharge of water vapor generated by boiling, thereby reducing mass transfer resistance. Additionally, numerous micrometer-sized small pores surrounding the finger-like pores provide sufficient capillary force to replenish liquid for the gas-liquid evaporation interface. Experimental results demonstrate that the introduction of finger-like pores in the wick increases gas and water permeabilities by 2.4 and 5.2 times, respectively. Furthermore, the superior heat and mass transfer performance of the bionic wick was demonstrated with an LHP. This work effectively addresses the conflicting demands of capillary force and flow resistance, enhancing the heat transfer performance of LHPs, which holds great promise for addressing heat dissipation challenges in high power density electronic chips and has potential applications in aviation, aerospace, and microelectronics for efficient thermal management.