Jianan Guo

This paper presents a novel large-span ring deployable perimeter truss for the mesh reflector deployable antennas, which is made up of two parts including a single-mobility driving mechanism and a ring deployable metamorphic mechanism. The mechanism design employs polygon approximation, and each side is treated as a basic unit using a modular design approach. By reasonable assembly, a ring deployable metamorphic mechanism with a small folded state and a large deployed state can be formed. Here, multiple singular positions, the axis of its three revolute joints being parallel and coplanar, are used in the fully deployed state, which forms multiple dead-center positions and changes the constraint conditions. The metamorphic motion is thus achieved, and a stable self-locking state is established that greatly enhances the stability. The paper first introduces the mechanism design and evaluation method; the kinematic and dynamic analysis is then conducted, and the simulation validation is also performed. Moreover, a principle design for cable-net structural setting and connection is illustrated. Finally, with the design of a driving system and the fabrication of a physical prototype, the deployable experiments are carried out, and the results show that the perimeter truss can efficiently act as the mesh reflector deployable antennas.

Laser directed energy deposition (L-DED) has emerged as a promising technique for rapid prototyping due to its cost-effectiveness and efficiency. However, the intricate and multi-scale physics of the process hinder its widespread application. This paper addresses the challenge by focusing on real-time identification of melt pool states to detect defects early and minimize resource wastage. To achieve this, a FixConvNeXt model was developed for fast and accurate monitoring of melt pool states. This model was trained using 5000 melt pool images captured during the printing of single-track deposits from a charge-coupled device. To evaluate its performance, FixConvNeXt was compared with other models using various metrics. Experimental results demonstrated that FixConvNeXt achieved superior performance in accurately identifying melt pool states with 99.1% accuracy, while also reducing computation burden and processing time. The mechanism of classification by FixConvNeXt was explained using gradient-weighted class activation mapping. The research findings highlight the potential application of online process monitoring in L-DED. This study lays the foundation for future development of an efficient deep learning network for automatic defect detection and feedback control.

The traditional data-driven models and pure physics models have been widely employed in quality prediction for additive manufacturing (AM). However, data-driven models rely on a large amount of labele...

In this paper, a simulation model for Selective Laser Melting (SLM) technology is established to simulate the additive manufacturing process of a turbine impeller for an aerospace engine. By utilizing the simulation model, variations in laser power and scanning speed are employed to obtain simulated results of thermal deformation for the turbine impeller under different laser power and scanning speed conditions. The results indicate that the thermal deformation of the component increases with the augmentation of laser power, decreases with the escalation of scanning speed, and eventually stabilizes. Based on the relationship between thermal deformation and energy, the energy utilization efficiency of the SLM process under different conditions is calculated. The findings demonstrate that, within a certain range of power, the synergistic effect of laser power and scanning speed allows for an increase in energy utilization efficiency and a reduction in processing time while ensuring the mechanical performance of the formed parts. Consequently, this approach proves effective in lowering production costs for complex components based on SLM technology.

The joint clearance of rudder loop has a significant impact in achieving the high-precision attitude control of aircraft. This study proposed a novel revolute joint clearance contact model considering surface topography. Such a model identified that the impact dynamic characteristics were significantly influenced by parameters such as contact speed, roughness, and curvature radius of asperities. The dynamic model of the rudder loop was based on the Lagrange equation and the contact model of revolute joint clearance. Results indicated that rudder angle error, contact force, and impact frequency non-linearly increased along with the increase of motor speed. The increment of joint clearance caused increased rudder angle error and contact force, but a decreased impact frequency. An increase in contact surface roughness decreased the contact force and exerted insignificant effects on rudder angle and impact frequency. To verify the dynamic model, a dynamic characteristic test rig of rudder loop was established. This study can improve the dynamic analysis accuracy of the rudder loop with clearance and provide a solid theoretical basis for solving the high-precision control of the discontinuous structure.

Cr5Mo steel with high thermal strength is frequently applied as the material for hydrocracking furnace tubes. Nonetheless, Cr5Mo tubes are prone to material failure in a high-temperature environment, threatening production safety. Considering that the IN718 nickel-base superalloy has favorable high-temperature oxidation resistance, the IN718 coating was fabricated on Cr5Mo substrate through laser cladding. The effect of process parameters on the high-temperature oxidation resistance of laser cladding IN718 coating was investigated. The results confirm that laser power and scanning speed affected the eutectic quantity precipitation of this layer, and the eutectic quantity precipitation was positively correlated with the mass gain of the coating. The high-temperature behavior of the coating could be divided into surface oxidation, intergranular corrosion, and material shedding. The scanning speed has a more significant impact on the high-temperature oxidation resistance. When the scanning speed is 15 mm/s, cracks originating in the heat-affected zone could exert a negative impact on the high-temperature oxidation resistance.