When machining complex curved parts on five-axis machine tools, due to factors such as the large curvature of the machining path and high feed acceleration, the tracking error of each axis cannot be controlled to be sufficiently small, resulting in difficulties in controlling the contouring accuracy. Coordinating the tracking error of each axis by matching servo gains emerges as a potential approach. However, existing gain solution methods are complex and time-consuming, rendering them inapplicable to actual production. In this paper, based on the explicit functional relationship between the contour error and the position loop gain (PLG) of each axis, a dynamic matching model for the PLG is established, and an intelligent control process for the linkage trajectory accuracy is proposed. Throug h “selfawareness” of the setpoint position and tracking error of each axis,“ self-analysis” of the position where the contour error of the linkage trajectory exceeds the limit, and“ self-decision” of the optimal contour error and the corresponding PLG, this intelligent control process can configure exclusive gains for different parts to ensure the machining accuracy of complex curved parts. For the KMC400 five-axis vertical machining center, the PLG of each axis is (70, 70, 80, 70, 75). After matching the exclusive gain (70, 68, 80, 59, 70) for the ruled surface A of the S–shaped test piece, the maximum contour error is reduced by 43.75%; after matching the exclusive gain (40, 70, 48, 40, 75) for the suction surface of the small blade of the impeller, the maximum contour error is reduced by 28.57%. The calculation time for the exclusive gains of the ruled surface A of the S–shaped test piece and the suction surface of the small blade of the impeller is 38.4 s and 5.7 s, respectively, meeting engineering application requirements.

Additive manufacturing, a quintessential disruptive manufacturing technology, empowers the production of intricate structures that are arduous to fabricate via traditional manufacturing approaches. It achieves this through “bottom-up” material accumulation. Cold spraying additive manufacturing technology, characterized by the high-speed collision deposition of solid-state metal powder, showcases remarkable technical advantages and application potential. This paper comprehensively deliberates on the concept, evolution, technological merits, and challenges of cold spraying additive manufacturing. Special emphasis is placed on its typical applications in the repair and remanufacturing of damaged components. The research reveals that cold spraying additive manufacturing technology presents benefits such as high deposition efficiency, strong bonding strength, and excellent coating density. Notably, it shows in the preparation of high-strength and high-plasticity deposition bodies, as well as the repair of complex components. Nevertheless, the technology still grapples with several challenges. These include inadequate deposition plasticity and toughness, a propensity for thin-walled components to deform and crack, and the relatively short lifespan of the nozzle. This paper synthesizes the research advancements of cold spraying additive manufacturing technology, pinpoints future development trends, and offers theoretical references and practical guidelines for the extensive application of this technology in aerospace, automotive manufacturing, and other sectors.

Resonant acoustic metamaterials have excellent sound absorption capabilities and show great potential for applications in aerospace, shipbuilding, and other fields. However, their low-frequency broadband sound absorption capabilities still need to be improved. To improve the synergistic sound absorption effect of low-frequency and broadband acoustic metamaterials, a Voronoi based random controllable acoustic metamaterial is proposed. The influence of the number and distribution of control points based on Voronoi segmentation method on the sound absorption performance of metamaterials was studied, and the robustness of controllable random structure sound absorption performance was analyzed. Multiple sets of test samples were prepared through additive manufacturing and impedance tube tests were conducted to verify the effectiveness of the simulation results. When the number of Voronoi control points is 20 and the number of scattered seeds is 26, the acoustic metamaterial exhibits a wide frequency absorption effect with multiple absorption peaks within 350–648 Hz, with an average absorption coefficient of 0.843. The thickness of this structure is 35 mm, which is only about 1/38 of the 350 Hz wavelength, providing a new idea for solving the problem of low-frequency noise control.

Mechanical metamaterials are a category of artificial structural materials and essentially composite structures constructed with artificial microstructure units, which aim to enhance mechanical properties of macroscopic overall structure by designing the shape, size and periodic arrangement mode of artificial microstructure units, and to achieve extraordinary mechanical properties such as negative Poisson’s ratio, multi-stability, lightweight and high strength, and programmability/reprogrammability. However, mechanical metamaterials fabricated by conventional materials are difficult to meet the performance requirements of multi-environmental field adaptability, rapid and controllable environmental response, and energy conversion for functional devices in different engineering application scenarios. Mechanically functional metamaterials constructed by combining mechanical metamaterials with advanced functional materials expand the performance of mechanical metamaterials from the material perspective, and can achieve tunable electro-mechanical, magneto-mechanical and thermo-mechanical coupling responses, which are expected to realize the multifunctional engineering applications of mechanical metamaterials. This review describes the extraordinary mechanical properties and typical classifications of mechanical metamaterials, detailly introduce the construction methods and coupling responses of three representative mechanically functional metamaterials, namely electro-mechanical, magnetomechanical and thermo-mechanical metamaterials, and summarizes and prospects the potential engineering applications of mechanically functional metamaterials in the fields of aerospace and marine engineering, including self-folding satellite solar wings, micro-spacecraft self-powered, satellite platform vibration isolation, marine engineering and equipment monitoring and sensing, and marine wave energy harvesting.

The radiation/receiving front end of active radio frequency (RF) systems such as phased array radars often needs to be equipped with the radome or electromagnetic (EM) window. As the typical structure-function integrated device, it protects systems’ internal structure from the external environment, and ensures EM waves can efficiently transmit in the working frequency band to ensure RF systems normally operate. Due to the need of sufficient stiffness and strength, the permittivity of radomes and EM windows is generally large, which is easy to reduce the wave-transparent performance and increase the insertion phase shift. Therefore, under the background that traditional technologies are gradually difficult to meet practical applications, it is urgent to explore EM anti-reflection (AR) technologies based on the new mechanism to improve the wave-transparent performance of traditional materials in the working bandwidth and angular domain. As two-dimensional metamaterials, metasurfaces have the ability of multi-dimensional EM regulation and conform to EM equipments’ mainstream development trend in geometric properties, which have important application value for EM AR technologies. This paper systematically introduces the research progress of metasurface EM AR technologies, first briefly reviews the typical traditional EM AR technologies, then mainly introduces the mechanism, design ideas and specific design architecture of metasurface EM AR technologies, and analyzes the characteristics of various EM AR metasurfaces, and finally summarizes and prospects the key problems and development trends in the field of EM AR technologies.

Targeting the complex geometric shapes and multi-level characteristics of metamaterials, a simulation and topology optimization method based on fixed grid techniques is proposed. Users do not need to manually partition finite element meshes which conform to geometric shapes, thereby significantly reducing preprocessing time. By employing quadtree/octree based local adaptive refinement, the accuracy of structural analysis can be ensured without increasing finite element analysis computational costs. And higher resolution topology optimization results can be generated. Based on the proposed method, a multifunctional metamaterial topology optimization model considering both load bearing and heat conduction was established. Numerical implementation and verification were conducted using a triply periodic minimal surface (TPMS) composite rib-reinforced structure as the optimization object. The proposed method has been implemented in OptFuture, a domestically developed and fully autonomous CAX industrial software. In addition, to address the multilevel weight reduction requirements of metamaterial structures, OptFuture is used to achieve multi-level lattice design and filling of metamaterials, thereby further expanding the potential for lightweight design of metamaterials.

High performance energy absorbing materials are urgently needed in the aerospace field. However, traditional energy-absorbing materials rely on plastic deformation and have the disadvantage of low reuse rate. In order to solve the above problems, this paper analyzes and studies the typical bistable metamaterial with strong reusable properties. Three types of mechanical metamaterial, namely sinusoidal beam element, articulated shell element and petal paper-cut element, are selected as the research objects, and parametric scanning method is adopted. The relationship of bistable characteristics, energy absorption characteristics and geometric parameters of metamaterial element is obtained by finite element simulation software. Three kinds of metamaterial units were prepared by additive manufacturing technology, and the simulation results were verified by mechanical compression tests. It provides a basis for the application of mechanical energy absorption in precision instruments and personnel protection.

The composite structure comprising case and skirt of a solid rocket motor (SRM) undergoes aging over prolonged periods of storage, consequently compromising reliability of the case structure of SRM. This study conducted an accelerated hot-humid aging test on typical materials of the skirt composite structure to assess its mechanical properties throughout the aging process. Additionally, microstructure parameters of the epoxy resin material presenting at the interface of the composite structure, i.e., the vulnerable spot, were characterized. Subsequent to the test, a cross-scale comparative analysis was performed to evaluate material damage at the composite structure’s interface. The results revealed that during accelerated aging, the epoxy resin matrix exhibited a gradual transition to a gully-shaped surface, with increasing surface damage severity correlated with the aging duration. The continuous rise in three-dimensional surface roughness contributed to material embrittlement and diminished toughness, resulting in a decline in the mechanical properties at interface of the composite structure. Analysis through Fourier transform infrared spectroscopy testing and X-ray photoelectron spectroscopy analysis further elucidated molecular-level damage to the epoxy resin matrix. As aging progressed, chemical reactions among the elemental groups were observed, reflecting potential oxidative crosslinking or decomposition reactions. Finally, a correlation analysis involving macroscopic and microscopic parameters was conducted to explain the cross-scale damage mechanism at the interface of the case composite structure.

Five-axis 3D printing equipment enables the printing of complex curved surfaces with varying curvatures, playing a significant role in the aerospace industry. Calibration is a crucial step in ensuring printing accuracy of such equipment. To achieve rapid calibration of five-axis 3D printing equipment and improve its printing precision, a calibration method utilizing a calibration object is proposed. Based on screw theory, a transformation model between the machine tool coordinate system and workpiece coordinate system of the five-axis 3D printing equipment is established, and the quantities to be calibrated are determined. A calibration object containing five calibration spheres is designed, and coordinates of the calibration spheres’ centers in the machine tool coordinate system are obtained using the least squares fitting method for sphere centers. An equation for calibrating the linear axes is established based on transformation relationship between the calibration coordinate system and machine tool coordinate system, while the rotational axes are calibrated using plane normal vector solving and the least squares fitting method for circles. 3D printing experiments are conducted based on the calibration results afterwards. Point cloud fitting analysis reveals that the average deviation of the printed samples by the five-axis 3D printing equipment after calibration reduced by 91.3% compared with before, significantly enhancing printing accuracy.

Copper-iron alloy has excellent electrical and thermal conductivity, excellent toughness and soft magnetic properties, and is an excellent electrical contact and electromagnetic shielding material, which has broad application prospects in electronic communication electrical contact devices and electromagnetic shielding equipment of aerospace, national defense and military industry. In this paper, copper-iron alloys with different copper mass fraction were prepared by double-wire arc additive manufacturing technology, and their microstructure, hardness, dynamic surface contact resistance and wear of carbon rods were tested by metallurgical microscope, Vickers hardness tester and currentcarrying friction and wear tester. The results demonstrate that as the copper mass fraction increases from 0 to 100%, the microstructure of the copper-iron alloy evolves from a continuous interlaced ferrite phase to a discrete spherical and dendritic distribution, ultimately forming a pure copper phase. At 60% copper mass fraction, the Cu-rich and Fe-rich phases exhibit the most uniform distribution. The hardness of the alloy initially increases and subsequently decreases with however, an excessive amount of copper leads to a decrease in hardness due to the increased presence of softer phases. The surface contact resistance progressively decreases with increasing copper content due to copper’s superior electrical conductivity. The wear of the carbon rod is influenced by the hardness of copper-iron alloys and the friction coefficient between the contact pairs, exhibiting a trend of first increasing and then decreasing: at low copper content, high hardness and friction coefficient exacerbate wear, while at high copper content, improved lubrication and heat dissipation performance mitigate wear.

Based on orthogonal experiment for minimum quantity lubrication (MQL) milling of Al–60% Si alloy, the influence of milling parameters on cutting force, cutting temperature and surface roughness is analyzed. Compared with dry cutting, the machining mechanism of MQL milling of high-silicon aluminum alloy is explored. The results show that under the condition of MQL milling, the cutting force is mostly affected by feed per tooth (f_z) and increases first and then decreases with increase of cutting speed (v_c). The impact of milling parameters on cutting temperature is: cutting speed > feed per tooth > radial cutting width. With the increase of v_c, the growth rate of cutting temperature increases from small to large. When v_c is 90 m/min, the inhibition effect of MQL on cutting heat is weakened with the highest cutting temperature. Surface roughness is significantly affected by f_z, which increases with the increase of f_z, and the lowest surface roughness is 0.234 μm. Compared with dry milling, feed force and tangential force of MQL processing reduces by 24.3% and 14.0%, respectively, cutting temperature reduces by 23.4% and surface roughness reduces by 13.7%. MQL assisted processing technology can effectively improve the milling performance of Al–60% Si alloy.