查看更多>>摘要：The deviation in wall thickness caused by core shift during the investment casting process significantly impacts the strength and service life of hollow turbine blades.To address this issue,a core shift limitation method is developed in this study.Firstly,a shift model is established based on computational fluid dynamics and motion simulation to predict the movement of the ceramic core in investment casting process.Subsequently,utilizing this model,an optimization method for fixtur-ing layout inside the refractory ceramic shell is devised for the ceramic core.The casting experiment demonstrates that by utilizing the optimized fixture layout,not only can core shift during the invest-ment casting pouring process be effectively controlled,but also the maximum wall thickness error of the blade can be reduced by 42.02％.In addition,the core shift prediction is also validated,with a prediction error of less than 26.9％.
查看更多>>摘要：Vibration-assisted grinding is one of the most promising technologies for manufacturing optical components due to its efficiency and quality advantages.However,the damage and crack propagation mechanisms of materials in vibration-assisted grinding are not well understood.In order to elucidate the mechanism of abrasive scratching during vibration-assisted grinding,a kine-matic model of vibration scratching was developed.The influence of process parameters on the evo-lution of vibration scratches to indentation or straight scratches is revealed by displacement metrics and velocity metrics.Indentation,scratch and vibration scratch experiments were performed on quartz glass,and the results showed that the vibration scratch cracks are a combination of inden-tation cracks and scratch cracks.Vibration scratch cracks change from indentation cracks to scratch cracks as the indenter moves from the entrance to the exit of the workpiece or as the vibra-tion frequency changes from high to low.A vertical vibration scratch stress field model is estab-lished for the first time,which reveals that the maximum principal stress and tensile stress distribution is the fundamental cause for inducing the transformation of the vibration scratch cracking system.This model provides a theoretical basis for understanding of the mechanism of material damage and crack propagation during vibration-assisted grinding.
查看更多>>摘要：The rapid development of additive manufacturing technology has offered a new avenue for designing and fabricating high wave-absorbing meta structures.In this study,the mechanical properties and broadband absorption performance of Poly-Ether-Ether-Ketone(PEEK)-based elec-tromagnetic wave-absorbing composite materials was investigated.The high-performance polymer PEEK was used as the matrix,and the materials with electromagnetic wave loss,such as reduced gra-phene oxide,Carbonyl Iron(CI),and Flake CI(FCI),were used as absorbers.Based on the theory of impedance matching,a wave-absorbing structure with a gradual impedance gradient was designed and printed.The test results showed that at the 2.0-18.0 GHz frequency band,the coverage rate of the effective absorption bandwidth was up to 72.0％,the average optimal reflectivity was-18.09 dB,and the wide-angle absorption range was 0°-30°.The advantages of additive manufactur-ing technology in designing and fabricating wave-absorbing structures are presented,demonstrating that the technology is an effective method for creating broadband absorbing structures.
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