查看更多>>摘要：Carbon Nanotubes(CNTs)reinforced Polymer-Matrix Composites(PMCs)is widely used as insulation materials in thermal protection system of aerospace propulsion.However,CNTs are prone to oxidation and have high thermal conductivities,which makes it difficult to improve the ablation resistance of insulation materials that contain CNTs.SiO2 was encapsulated onto the sur-face of CNTs(CNTs@SiO2),which were then added to Ethylene Propylene Diene Monomer(EPDM)rubber to prepare the insulation materials.Thermogravimetric analysis and ablation test were used to evaluate the resistance of the insulation materials to thermal oxidation and ablation.Additionally,scanning electron microscopy was performed to analyze their microstructures.Results revealed that the addition of CNTs@SiO2 could visibly reduce the effects of hot corrosion and abla-tion on insulation materials.The C-CNTs@SiO2-1 formulation had the best ablative resistance.Further,compared with the unencapsulated formulation(C-CNTs-10),the C-CNTs@SiO2-1 for-mulation reduced the line ablation rate by 51％to 0.0130 mm/s after oxygen-acetylene experiments.Lastly,the ablation mechanism was investigated based on the effects of the CNTs@SiO2 additive on their properties.Thus,the improvement in ablation performance may be attributed to CNTs@SiO2-induced decreases in thermal conductivity,improvement in the hot corrosion resis-tance in the char layer,and changes in the microstructure.
查看更多>>摘要：As the controlled research of Dynamic Installation(DI)and Static Installation(SI),a new interference installation method was developed based on electromagnetic loading to enhance the mechanical properties of composite structures.Four different interference-fit sizes were consid-ered,ranging from a net fit to 2.0％.The experiments were conducted to evaluate the installation resistance and the mechanical behavior of the joint under external loads.Meanwhile,an FEA model to model the stress distribution and damage behavior of the bolt-hole contact interface was estab-lished.The load-displacement curve and damage modes of experiments were used to verify the FEA results.The results show that the installation resistance during DI process was remarkably lower than that of SI process corresponding to all interference-fit sizes,and the stress amplitudes induced by interference were larger and widely distributed.The damage of the hole wall was positively cor-related with interference fit size,but DI can significantly reduce the damage compared to SI.In per-formance tests,DI enhanced the static bearing capacity and extended longer fatigue life of the joints than SI.DI methods can be an effective way to achieve highly reliable interference joints in com-posite structures.
查看更多>>摘要：Lunar dust is considered to be one of the top challenges for enabling humans to have extended stays on the moon.Human activities such as module landings and launches,walking,rover operation and construction activities will inevitably produce a significant amount of dust.Therefore,it is important to estimate the potential range and intensity of dust deposition caused by these activities to minimize dust accumulation over time and for maintenance planning and exe-cution.A modular model that correlates the dust deposition distribution with initial mean dust par-ticle velocity,its mean ejected angle and the total amount of ejected mass is developed for an elementary mechanical movement.This modular model is further employed to form a modeling framework to estimate dust deposition of a trajectory based activity of similar repeated movements such as the landing process of a lander,walking and rover operation.The model forms a unified modeling framework for different trajectory-based activities and is shown to predict consistent and physically meaningful ranges and intensities of dust deposition provided reliable data to cali-brate the model parameters.
查看更多>>摘要：Adhesively Bonded Carbon Fibre Reinforced Plastic(CFRP)and titanium alloy have been extensively used as a hybrid structure in modern aircrafts due to their excellent combination of mechanical properties and chemical stabilities.This study utilised NaOH anodising method to create micro-rough titanium surfaces for enhancing adhesive bonding between titanium alloy and CFRP laminates.A special and simple technique named Resin Pre-Coating(RPC)was also employed to improve the surface wetting of anodised titanium and grinded CFRP substrates.The influences of anodising temperature and duration on the surface morphology,wettability and adhesive bond strength were investigated.The single lap shear test results showed that the bond strength of specimens anodised at 20 ℃ for 15 min improved by 1 35.9％and 95.4％,respectively,in comparison with that of acid pickled and grinded specimens(without RPC treatment).Although increasing the anodising temperature and duration produced rougher titanium surfaces,the adhe-sively bonded joints were not strong enough due to relatively friable titanium oxide layers.
查看更多>>摘要：Electrically Assisted Forming(EAF)technology has obvious advantages in material forming.To develop an effective constitutive model considering electrical effects,room temperature and electrically assisted quasi-static uniaxial tensile tests were conducted using ultrathin nickel-based superalloy plates with a thickness of 0.25 mm.The research focused on the two most widely recognized effects:the Joule thermal and the electric athermal effects.The mechanism of current action can be divided into two scenarios:one considering the Joule thermal effect only,and the other considering both effects simultaneously.Two basic constitutive models,namely the Modified-Hollomon model and the Johnson-Cook(J-C)model,were selected to be optimized through the classification of two different situations,and four optimized constitutive models were proposed.It was found that the J-C model with simultaneous consideration of the Joule thermal effect and electric athermal effect had the best prediction effect by comparing the results of these four models.Finally,the accuracy of the optimization model was verified by finite element simula-tion of the electrically assisted stretching optimization model.The results show that the constitutive model can effectively predict the temperature effect caused by the Joule heat effect and the athermal effect of current on the material.
查看更多>>摘要：The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high demands on its application.To achieve this objective,this study investigates the impact of three distinct brazing temperatures and five typical grain sizes on the brazed joints'me-chanical properties and microstructure evolution process.Microstructural evolution analysis was conducted based on Electron Back Scatter Diffraction(EBSD),Scanning Electron Microscopy(SEM),X-Ray Diffraction(XRD),High-Resolution Transmission Electron Microscopy(HRTEM),and Focused Ion Beam(FIB).Besides,the mechanical properties and fracture behavior were studied based on the uniaxial tension tests and in-situ tension tests.The findings reveal that the brazing joint's strength is higher for the fine-grain capillary than the coarse-grain one,primarily due to the formation of a dense branch structure composed of G-phase in the brazing seam.The effects of grain size,such as pinning and splitting,are amplified at higher brazing temperatures.Addition-ally,micro-cracks initiate around brittle intermetallic compounds and propagate through the eutec-tic zone,leading to a cleavage fracture mode.The fracture stress of fine-grain specimens is higher than that of coarse-grain due to the complex micro-crack path.Therefore,this study contributes significantly to the literature by highlighting the crucial impact of grain size on the brazing proper-ties of ultra-thin-walled Inconel 718 structures.
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