查看更多>>摘要：The particle acceleration behavior and deposition mechanism of cold spraying aluminum matrix composites(Al2O3/2024)are complicated by the addition of ceramic particles.The effects of different feeding rates and particle diameters on critical velocity and mechanical properties were studied by numerical simulation and experiment.The results indicate that as the powder feeding rate increases,the impact velocity of gas and particles gradually decreases,and the temperature of gas and particles increases,resulting in an increase in the difference between particle impact velocity and critical velocity.The highest tensile strength of the deposit is achieved at a powder feed-ing rate of 1 r/min,which is 343 MPa.As the powder feeding rate increases,the performance of the deposits decreases,but it significantly saves time and cost.As the particle diameter increases,the impact temperature first increases and then decreases,resulting in the critical velocity first decreas-ing and then increasing,and the mechanical performance first increasing and then decreasing.To some extent,the best performance of the deposit is achieved when the size of the metal particle is close to that of the ceramic particle.
查看更多>>摘要：In this paper,a visual servoing approach is developed to capture the docking rings of tumbling non-cooperative satellites with a space manipulator.The primary challenge addressed is the potential for the docking ring to leave the monocular camera's field-of-view as the manipulator approaches the target,due to the ring's large size.To solve this issue,a two-phase visual servoing scheme combining a monocular camera and a three-line structured light vision system is proposed.In an effort to augment the success rate and safety of capture operations,several constraints are formulated,encompassing manipulator's kinematics,monocular camera's field-of-view,obstacle avoidance,structured light's breakpoints and smooth capture.Subsequently,a nonlinear model predictive controller is proposed to manage these constraints in real-time and regulate the system.System models are established based on image moments and pose for each phase,selecting these features as visual feedback to simplify the formulation of servo constraints and avoid the complex circle-based pose measurement.Furthermore,to ensure unbiased predictions,the model distur-bances arising from the imprecise estimation of target motion parameter are observed using an extended Kalman filter,which are then incorporated into the predictive control framework.The simulation results demonstrate the effectiveness of this scheme.
查看更多>>摘要：SiCp/Al composites are used in aerospace and deep-space exploration equipment because of their extremely high strength and thrust-to-weight ratios;however,the differences in the properties of the reinforcement and matrix materials in this type of composites have restricted their applications.The ultrahigh-frequency vibration characteristics of ultrasonic vibration process-ing technology can effectively solve the above bottlenecks,but the effect of high-frequency vibration on the interfacial properties of SiCp/Al composites is still unclear.The effects of ultrasonic vibra-tion on the interface strength of composites were analyzed from a microscale perspective by means of single particle push-out Molecular Dynamics(MD)simulations and tests under different condi-tions.The results show that the interface strength is negatively correlated with particle size but pos-itively correlated with ultrasonic amplitude,with a maximum increase of about 51％relative to no ultrasound.Brittle-plastic transition was observed on the surface of particles with high interface strength,and lateral microcracks due to stress concentration were present on the surface of particles with low interface strength.Higher strains and grain refinement were obtained for larger ampli-tudes,and stacking faults and tangle dislocations appeared on the side of the interface layer close to the Al matrix.The results provide potential insights to improve the micromechanical and mechanical properties of SiCp/Al composites,enhance the longevity of the materials,and realize the sustainable use of resources by expanding the efficient,precise,and clean machining of such materials.
查看更多>>摘要：Processing microchannels inside laminated aluminum nitride high-temperature co-fired ceramics(AlN HTCC)packaging,a typical difficult-to-cut ceramic,can effectively solve the heat-dissipation problem of integrated chips used in smart skin.In order to improve the processing effi-ciency and quality of AlN,the machinability of AlN after laser chemical milling(LCM)was studied through the milling force,machined surface quality,surface defects,formation mechanism,and tool wear.This study established a milling force model that can predict the milling forces of AlN and anal-yses the reasons for the improvements in the milling force based on experimental data and predicted data.The results from the model and experiments demonstrated that the milling force of the laser chemical milling assisted micro milling(LCAMM)decreased by 85％-90％and 85％-95％,respec-tively,due to the amount of removal of a single edge was more uniform and the actual inclination angle increased during the cutting process in LCAMM.Moreover,the machined surface quality improved by 65％-76％after LCM because of less tool wear,fewer downward-propagating cracks generated during each feed,and the surface removal mode transformed from intergranular fracture to transgran-ular fracture,which effectively reducing tool wear and improving tool life.Finally,when feed per tooth and depth of cut were 0.4 μm/z and 5 μm,the optimal machined surface quality was obtained,with a roughness of 64.6 nm Therefore,milling after LCM can improve the machinability of AlN and pro-viding a feasibility for the high-quality and efficient machining of microchannels.
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