摘要 ：

The nickel-based GH4169 superalloy is widely used in the aerospace field, which has desirable oxidation resistance and strength in extreme environments. However, the size effect and underlying microstructural mechanism in the cyclic deformation of the GH4169 sheet are still not fully elucidated, which affects the forming accuracy precision of thin-walled components. To this end, the cyclic mechanical properties and microstructural evolution of the GH4169 sheets with different thicknesses and grain sizes were systematically investigated via cyclic shearing tests. The superalloy sheet exhibits obvious early re-yielding, instantaneous softening and permanent softening during the cyclic deformation and these cyclic deformation behaviors are obviously affected by size effect. To rationalize the cyclic mechanical responses and size effect, transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) tests were conducted. The results indicated that the dislocation slip patterns are principally planar array slip and cross slip in the cyclic shearing deformation. Meanwhile, the annihilation of unstable dislocation and the presence of carbides led to the instantaneous softening. Moreover, the change of loading direction, the reduction of texture strength, the proportion of low-angle grain boundary (LAGB), and geometrically necessary dislocation (GND) density together result in the occurrence of permanent softening. Based on the comparative analysis of the microstructure evolution of superalloy sheets with different size factors, the underlying mechanism of size effect on cyclic deformation was clarified. The findings in the research combine the cyclic mechanical response and microstructure evolution closely in the cyclic deformation of superalloy sheets and deepen the understanding of size effect under complex loading paths.

关键词 ：

Microstructure evolution Size effect Deformation mechanism Cyclic shearing Nickel-based superalloy

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In the areas of aerospace and military industry, wheeled vehicles are expected to have the ability of passing various ground surfaces, including lunar soil, sand, marsh, mud flat, etc. This makes vehicle trafficability on soft ground become a very hot research topic. There are very a few difficulties in the present research of vehicle trafficability on soft ground, such as obtaining wheel-ground interaction information, inaccurate identification of soil mechanical characteristics parameters, and single evaluation index. In this paper, a novel approach of evaluating the vehicle trafficability on soft ground using wheel force information is proposed. As parts of the proposed approach, the methods of obtaining wheel force information, identification of soil mechanical characteristics parameters and integated method of trafficability evaluation, are discussed in detail. The proposed approach was validated through a practical test.

关键词 ：

Trafficability wheel force soil mechanical property parameters

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An increasing number of cutting tools with different geometric shapes are needed owing to the increasing complexity of the workpiece surfaces in aerospace and automotive molding. A new kind of milling cutter is designed, which is named as revolving lemniscate milling cutter (RLMC for short). The parametric mathematical models of RLMC are proposed. Mathematical models of cutting edge curves are proposed to provide the theoretical basis for RLMC precision manufacturing. Equivalent helix angle, curvature radius of tool rotation surface, effective cutting linear velocity, and scallop height are studied. Corresponding numerical simulation results are also provided as graphical representations. Three RLMC with different tool parameters are manufactured, and contrast experiments are conducted to prove that using RLMC in end milling can achieve better machining quality. The parametric design and application research provide a new method and theoretical basis for other new types of milling cutters.

关键词 ：

Milling cutter Cutting tool design Rotational lemniscate end mill End milling Cutting performance

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Al2O3 ceramic have excellent chemical inertness, superior heat resistance, and excellent corrosion resistance, so they are considered ideal materials for manufacturing high-performance components such as thermal end devices in aerospace, heat dissipation panels in electronic communication, and exhaust filters in the automotive industry. Digital Light Processing (DLP) is a useful technology to fabricate complex Al2O3 ceramic components. However, the size shrinkage effect of DLP-fabricated components need to be investigated deeply before its further application. In this work, we utilized DLP technology to fabricate Al2O3 ceramic honeycomb structures and systematically investigated their microstructure, size shrinkage, and mechanical properties. Our findings revealed that the Al2O3 ceramic grains exhibit flake-like structures with an average diameter of 1-2 mu m, and the ceramic particles are tightly bonded. The shrinkage rates in the X and Y axes were 7.54 % and 7.42 %, respectively, while the Z-axis exhibited a more significant shrinkage of 13.04 %. This anisotropic shrinkage in different direction was attributed to accumulation of the interlayer bonding under gravity action during debinding and sintering process. The compressive stress-strain curve of the honeycomb structures demonstrated a typical brittle compressive behavior, including elastic, stress plateau, and brittle fracture stages. The honeycomb structures exhibited an elastic modulus of 54.49 +/- 1.22 MPa and a compressive strength of 10.22 +/- 0.42 MPa. The fracture analysis indicated that the fractures region of honeycomb structures initiated at the corners of the honeycomb structures, indicating their easy-broken compared to the walls. These findings provide valuable guidance for the high- precision and high-performance manufacturing of complex Al2O3 ceramic components.

关键词 ：

Size shrinkage Digital Light Processing Compressive properties Honeycomb structure

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Titanium alloys are widely used in aerospace and other fields due to their advantages of low density, high specific strength and good corrosion resistance. Laser oscillating welding is an innovative process in the realm of welding technology. In this study, two laser oscillating welding methods (circular and linear) were employed to analyze the influence of different oscillation parameters on the formation of titanium alloy. The results indicate that the oscillation frequency has a significant impact on weld formation. The laser scanning trajectory also affects weld formation, with circular and linear scanning trajectories resulting in better weld quality. Finally, the effects of oscillation modes on the microstructure and properties of laser oscillating welding titanium alloy were investigated based on optimized process parameters. Among them, circular laser oscillating welding of titanium alloy exhibits higher tensile strength, with a maximum tensile strength of up to 1188.3MPa.

关键词 ：

Laser oscillating welding properties formation microstructure titanium alloy

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Directed Energy Deposition (DED), a branch of AM processes, has emerged as a significant technique for fabricating large metal components in sectors such as aerospace, automotive, and healthcare. DED is characterized by its high deposition rate and scalability, which stand out among other AM processes. However, it encounters critical issues such as residual stresses, distortion, porosity, and rough surfaces resulting from rapid melting and solidification. As a novel advancement, Ultrasonic-Assisted Directed Energy Deposition (UA-DED) integrates ultrasonic oscillations into DED aimed at addressing these challenges. Herein, the latest research related to the UA-DED process and the current major challenges of the DED process, residual stresses, porosity, and crack defects are critically reviewed. Subsequently, the paper also details the working principle and system components of UA-DED technology and reviews the material improvement by introducing UA into the DED process, grain, porosity, tensile properties, and deposition defects. The most critical optimization methods of process parameter variables for UA and the different material interaction mechanisms between UA and DED processes are identified and discussed in detail. Finally, the perspectives on the research gap and potential future developments in UA-DED are also discussed.

关键词 ：

directed energy deposition ultrasonic-assisted strengthening effect process parameters metal additive manufacturing

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This article considers a class of hyperbolic-parabolic partial differential equation (PDE) system with some interior mixed-coupling terms, a rather unexplored family of systems. The family of systems we explore contains several interior-coupling terms, which makes controller design more challenging. Our goal is to design a boundary controller to exponentially stabilize the coupled system. For that, we propose a controller whose design is based on the backstepping method. Under this controller, we analyze the stability of the closed loop in the $H<^>{1}$ sense. A set of (highly coupled) backstepping kernel equations is derived, and their well-posedness is shown in the appropriate spaces by an infinite induction energy series, which has not been used before in this setting. Moreover, we show the invertibility of transformations by displaying the inverse transformations, as required for closed-loop well-posedness and stability. Finally, a numerical simulation is implemented, and the result illustrates that the control law designed by the backstepping transformation can stabilize the mixed PDE system exponentially.

关键词 ：

Aerospace electronics Couplings Kernel Mathematical models Backstepping control mixed-coupling terms Boundary conditions Numerical stability Backstepping hyperbolic-parabolic system

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Hybrid lattice structures have significant potential in engineering applications owing to their outstanding mechanical and thermal properties. In this paper, an innovative design strategy for hybrid lattice structures is proposed involving the integration of primitive surfaces with truss lattice configurations. This approach allows for the full exploitation of the mechanical and thermal properties inherent in each component, leading to the development of new hybrid lattice structures. Firstly, the quasi-static compression and fluid-solid coupling heat conduction analysis of the hybrid lattice structure is carried out by numerical simulation. Then the effects of surface wall thickness, and truss diameter on the mechanical and thermal properties of the lattice structure are discussed. Additionally, the mechanical performance of the array hybrid lattice structure is evaluated through quasi-static compression experiments. These experimental results are compared with those from the numerical simulations, validating the accuracy of the simulation model. Finally, a multi-objective optimization model targeting specific elastic modulus and heat dissipation performance (indicated by Nusselt number) is established, in response to the demand of aviation and aerospace industries for lightweight, load-bearing, and heat- dissipating multi-functional integrated lattice design. The non-dominated sorting genetic algorithm is utilized to solve the optimal model, and the distribution of feasible solutions and Pareto front are obtained. The results show that the interpenetrating hybrid lattice structure has a greater improvement in mechanical and thermal properties than the primitive surfaces. This research holds significant implications for the design of multi- performance hybrid lattice structures.

关键词 ：

Thermal property Mechanical property Hybrid lattice structure Triply periodic minimal surfaces Multi-objective optimization

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Developing high-performance metallic materials with high yield strength and excellent ductility is important for various applications, such as automobiles, power plants, and aerospace industries. However, conventional alloys typically exhibit a trade-off between strength and ductility, making it difficult to develop materials that are both strong and ductile. In this study, we report that a cast Co-Cr-Fe-Ni-Al alloy can achieve a high room temperature yield strength of up to 500 MPa, which is twice that of conventional high-entropy alloys (HEAs) with face- centered cubic structures, with a tensile strain of 29 %. After thermomechanical treatment, the alloy exhibits even better synergy of strength and ductility, with a yield strength of 900 MPa and 30 % elongation. These exceptional mechanical properties are conferred by a multiscale hierarchical heterostructure, which was introduced through careful control of the alloy composition using a negative enthalpy alloy design strategy. The heterostructure ranges from the micrometer to sub-micrometer and nanometer scales. This multiscale hierarchical structure acts as a continuous impediment to dislocation motion, greatly increasing strength, and facilitating hetero-deformation induced hardening via strain partitioning, resulting in sustained ultrahigh strain hardening. Importantly, multiscale hierarchical heterostructures facilitate coordinated plastic deformation and multiple plastic deformation mechanisms, and stress concentration relieving, and play important roles in improving ductility. This work reveals the effect of different types (and scales) of heterogeneities on the deformation mechanism of HEAs and opens new perspectives for constructing heterostructures, which serve as a new design approach for high strength and excellent ductility by using a negative enthalpy alloy design strategy.

关键词 ：

Multiscale hierarchical heterostructure Strength and ductility Negative enthalpy alloy Dislocation Strain hardening

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The H2/O2 internal combustion is promising to be adopted as auxiliary power by combusting the wasted hydrogen in the upper stages under aerospace conditions. Concerning no inert gases participating the combustion, the control of H2/O2 heat release is a great challenge. This paper proposes to control the heat release by adopting an active pre-chamber (PC). All the combustion consumed oxygen is injected into the PC. The combustion of oxygen and small amount of pre-existed H2 in PC increases the PC pressure, enabling the hot reactant and massive oxygen to be injected into the main chamber (MC) to arrange the oxygen jet induced hydrogen diffusive combustion. The test was conducted on a constant volume combustion bomb (CVCB) to explore the effects of equivalence ratio (phi G) and orifice diameter on the diffusive H2/O2 combustion characteristics. The results showed that increasing phi G resulted in the decreased premix combustion fraction and prolonged combustion duration. The peak pressure of MC dropped with phi G indicating the ability of adjusting engine load by varying phi G. The heat release process could be controlled either by phi G or orifice diameter. Properly increasing the orifice diameter availed shortening the combustion duration and promoting the heat release efficiency.

关键词 ：

Upper Stage Auxiliary Power Units Combustion Jet diffusion Oxygen Hydrogen Internal Combustion Engine

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