We use dislocation theory and molecular dynamics （MD） simulations to investigate the effect of atom properties on the macroscopic strain rate sensitivity of f cc metals. A method to analyse such effect is proposed. ...We use dislocation theory and molecular dynamics （MD） simulations to investigate the effect of atom properties on the macroscopic strain rate sensitivity of f cc metals. A method to analyse such effect is proposed. The stress dependence of dislocation velocity is identified as the key of such study and is obtained via 2-D MD simulations on the motion of an individual dislocation in an fcc metal. Combining the simulation results with Orowan＇s relationship, it is concluded that strain rate sensitivities of fcc metals are mainly dependent on their atomic mass rather than the interatomic potential. The order of strain rate sensitivities of five fcc metals obtained by analysing is consistent with the experimental results available.展开更多
Wear is a prevalent issue across various industries. Spherical fused tungsten carbide (sFTC) reinforced nickel-aluminum bronze (NAB) matrix composite surface deposits have shown remarkable potential in mitigating wear...Wear is a prevalent issue across various industries. Spherical fused tungsten carbide (sFTC) reinforced nickel-aluminum bronze (NAB) matrix composite surface deposits have shown remarkable potential in mitigating wear by approximately 80%. However, the performance of these sFTC/NAB composite surface deposits is determined by their residual stress state, and the precise macroscopic and microscopic residual stresses within these composites have yet to be clearly established. To address this gap, we employed neutron diffraction to measure the residual stresses in the sFTC/NAB composite surface deposits and re-melted NAB samples produced via laser melt injection. Significant residual stresses were determined. The maximum tensile macro residual stress appears approximately 1-1.5 mm below the composite layer. Residual stresses accumulate with an increasing number of laser process tracks. The maximum tensile macro residual stress in the three-track samples reaches about 350 MPa. Preheating the base plate significantly reduces the levels of macroscopic residual stress. The WC phase displayed significant compressive thermal misfit residual stress magnitude, while the Cu matrix exhibited tensile thermal misfit residual stress. Preheating the base plate does not reduce microscopic thermal misfit residual stress levels. In addition, a finite element model was built to investigate temperature and residual stresses in the re-melted NAB samples. The predicted temperature history and residual stress agree with the experimental results.展开更多
The current research and development of magnesium alloys is summarized. Several aspects of magnesium alloys are described： cast Mg alloy, wrought Mg alloy, and novel processing. The subjects are discussed individuall...The current research and development of magnesium alloys is summarized. Several aspects of magnesium alloys are described： cast Mg alloy, wrought Mg alloy, and novel processing. The subjects are discussed individually and recommendations for further study are listed in the final section.展开更多
The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled ...The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled hierarchical multiscale modeling methods. Measurements showed that the macroscopic and total RSes had the largest variations in the longitudinal direction(LD). Increasing the welding speed led to higher values of measured LD macroscopic and total RSes in the matrix. The welding speed also significantly influenced the distributions and magnitudes of the microscopic RSes. The RSes were predicted via an improved hierarchical multiscale model, which includes a constant coefficient of friction based thermal model. The RSes in the composite plates before friction stir welding(FSW) were computed and then set as the initial states of the FSW process during modeling. This improved decoupled multiscale model provided improved predictions of the temperature and RSes compared with our previous model.展开更多
One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites(CNT/Al)composites is the load transfer strengthening mechanism(LTSM).However,a fundamental issue concerning...One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites(CNT/Al)composites is the load transfer strengthening mechanism(LTSM).However,a fundamental issue concerning the LTSM is that quantitative measurements of load partitioning in these composites during loading are very limited.In this study,in-situ neutron diffraction study on the tensile deformation of the 3 vol.%CNT/2009 Al composite and the unreinforced 2009 Al alloy was conducted.The{311}and{220}diffraction elastic constants(DECs)of the 2009 Al alloy were determined.Using those DECs the average stress in the 2009 Al matrix of the composite was calculated.Then the average stress in the CNTs was separated by using the stress equilibrium condition.Computational homogenization models were also applied to explain the stress evolution in each phase.Predicted results agree with experimental data.In the present case,the average stress in the CNTs reaches 1630 MPa at the yield strength of the composite based on linear regression of the measured data,which leads to an increment of yield strength by about 37 MPa.As the result of this work,an approach to quantify load partitioning in the CNTs is developed for the CNT/Al composites,which can be applied to optimize the mechanical properties of the composites.展开更多
An investigation was carried out to modify the toughness of triethylene tetramine cured DGEBA （diglycidyl ether of bisphenol-A） resin using solid amine terminated poly （ethylene glycol） benzoate （ATPEGB） as modi...An investigation was carried out to modify the toughness of triethylene tetramine cured DGEBA （diglycidyl ether of bisphenol-A） resin using solid amine terminated poly （ethylene glycol） benzoate （ATPEGB） as modifier with and without red mud waste particles. The solid ATPEGB modifier synthesized from the acid catalyzed esterification reaction of poly （ethylene glycol） （PEG） and 4-amino benzoic acid was characterized by Fourier transform infrared spectroscopy （FT-IR） and ^1H-NMR （nuclear magnetic resonance） spectroscopies, viscosity measurements, and solubility parameter calculation. The unfilled and red mud waste filled modified epoxy networks were evaluated with impact, adhesive, tensile, flexural and thermal properties by differential scanning calorimetry （DSC）, thermogravimetric （TG） and dynamic mechanical analysis （DMA）. The effect of modifier concentration and red mud waste particles on toughening behavior was also investigated. The optimum properties were obtained at 12.5 phr （parts per hundred parts of resin） concentration of the modifier. The ATPEGB modified cured epoxy was thermally stable up to 315℃. The morphology on fracture surfaces of cured epoxy was also analyzed by scanning electron microscopy （SEM）.展开更多
N^+ ion irradiation is utilized to tune the structure and mechanical properties of a Cu48Zr47.2Al4Nb0.8 bulk metallic glass composite(BMGC). Ion irradiation increases the disorder near the surface, as probed by neutro...N^+ ion irradiation is utilized to tune the structure and mechanical properties of a Cu48Zr47.2Al4Nb0.8 bulk metallic glass composite(BMGC). Ion irradiation increases the disorder near the surface, as probed by neutron diffraction, and, moreover, causes the phase transformation from B2Cu Zr to B19’ CuZr martensitic phase in the studied BMGC. The tensile plasticity of the BMGC is dramatically improved after ion irradiation, which results from multiple shear banding on the surface and the martensitic transformation of the B2 to B19’ Cu Zr martensitic phase. The experimental results are strongly corroborated by complementary molecular dynamic simulations.展开更多
A statistical approach is developed, based on a Monte Carlo method, in order to determine the statistical composition of a polyamide-6 sample composed of caprolactam （an AB-type monomer） and of a di-acid （A2 type）...A statistical approach is developed, based on a Monte Carlo method, in order to determine the statistical composition of a polyamide-6 sample composed of caprolactam （an AB-type monomer） and of a di-acid （A2 type） or a tri- acid （A3 type） as coupling agents. For this composition, the linear theological behavior of these systems is predicted using a tube-based theory. This allows us to show that while coupling agents of type A2 can be seen as flow improver, the effect of branching agents of type A3, depending on the synthesis recipe and the conversion level, can lead either to an increase or to a decrease of the viscosity. By adding specific amount of these agents, we also show that it is possible to obtain materials with the same zero-shear viscosity but with different shear thinning behavior. Furthermore, the polydispersity of linear samples of the same average number molecular weight, Mn, is discussed in function of the amount of A2 monomers they contain. Ranging from 2 to 1.5, this difference in polydispersity is expected to have a significant influence on the processing behavior of such materials.展开更多
This paper reports that InAs/In0.53Ga0.47As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current dens...This paper reports that InAs/In0.53Ga0.47As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current density of 3kA/cm^2 has been obtained for diodes with AlAs barriers of ten monolayers, and an Ino.53Ga0.47As well of eight monolayers with four monolayers of InAs insert layer. The effects of growth interruption for smoothing potential barrier interfaces have been investigated by high resolution transmission electron microscope.展开更多
Hybrid proton conducting membranes of poly（vinyl alcohol） （PVA） and phosphomolybdic acid （PMA） were prepared by solution casting method. The effect of PMA doping and PVA crosslinking density on the membrane prop...Hybrid proton conducting membranes of poly（vinyl alcohol） （PVA） and phosphomolybdic acid （PMA） were prepared by solution casting method. The effect of PMA doping and PVA crosslinking density on the membrane properties and proton conductivity were investigated. The crosslinking reaction between the hydroxyl group of PVA and the aldehyde group of glutaraldehyde （GA） was characterized by IR spectroscopy. Proton conductivity of the membranes increases with an increase in concentration of the doped PMA and also with an increase in crosslinking density of the membranes. Proton conductivity results indicate that a significant amount of PMA was maintained in the membranes even after several hours of immersion in water. A maximum conductivity of 0.0101 S cm^-1 was obtained for the membrane with 33.3 wt% PMA and crosslinking density of 5.825 mol%. X-ray diffraction studies were carried out to investigate the influence of PMA doping and crosslinking density on the nature of the membranes. These properties make them very good candidates for polymer electrolyte membranes for direct methanol fuel cell application.展开更多
Low-value,renewable,carbon-rich resources,with different biomass feedstocks and their derivatives as typical examples,represent virtually inexhaustive carbon sources and carbon-related energy on Earth.Upon conversion ...Low-value,renewable,carbon-rich resources,with different biomass feedstocks and their derivatives as typical examples,represent virtually inexhaustive carbon sources and carbon-related energy on Earth.Upon conversion to higher-value forms(referred to as“up-carbonization”here),these abundant feedstocks provide viable opportunities for energy-rich fuels and sustainable platform chemicals production.However,many of the current methods for such up-carbonization still lack sufficient energy,cost,and material efficiency,which affect their economics and carbon-emissions footprint.With external electricity precisely delivered,discharge plasmas enable many stubborn reactions to occur under mild conditions,by creating locally intensified and highly reactive environments.This technology emerges as a novel,versatile technology platform for integrated or stand-alone conversion of carbon-rich resources.The plasma-based processes are compatible for integration with increasingly abundant and cost-effective renewable electricity,making the whole conversion carbon-neutral and further paving the plasma-electrified upcarbonization to be performance-,environment-,and economics-viable.Despite the chief interest in this emerging area,no review article brings together the state-of-the-art results from diverse disciplines and underlies basic mechanisms and chemistry underpinned.As such,this review aims to fill this gap and provide basic guidelines for future research and transformation,by providing an overview of the application of plasma techniques for carbon-rich resource conversion,with particular focus on the perspective of discharge plasmas,the fundamentals of why plasmas are particularly suited for upcarbonization,and featured examples of plasma-enabled resource valorization.With parallels drawn and specificity highlighted,we also discuss the technique shortcomings,current challenges,and research needs for future work.展开更多
Graphene, an extraordinary allotropy of carbon, the 2D nanosheet, have been synthesized through exfoliation of graphite in ortho dichloro benzene by sonication. The morphological changes in different interval of sonic...Graphene, an extraordinary allotropy of carbon, the 2D nanosheet, have been synthesized through exfoliation of graphite in ortho dichloro benzene by sonication. The morphological changes in different interval of sonication have been investigated by Scanning Electron Microscopy (SEM) andTransmission Electron Microscopy (TEM). Raman Spectra confirmed the formation of defect free Graphene sheets. As prepared Graphene showed high thermal stability under N2 atmosphere. It has been observed that sonication for 4 hours, effectively exfoliates graphite to form Graphene sheets. However, further sonication leads to restacking of Graphene sheets. The formation of Graphene is supposed to be due to the Sonopolymerization of the solvent (ortho-dichloro benzene)and graphite solvent interaction.展开更多
Nowadays with ever increasing demand of energy, developing of alternative power sources is an important issue all over the world. In this respect we have prepared nanocomposites based on metal oxide (titanium oxide) c...Nowadays with ever increasing demand of energy, developing of alternative power sources is an important issue all over the world. In this respect we have prepared nanocomposites based on metal oxide (titanium oxide) coated multiwalled carbon nanotubes (MWCNTs)/polyaniline (PANI) with graphene and without graphene and studied their electrochemical performance. The formation of the polymer in the nanocomposites was confirmed by the Fourier Transform Infrared Spectroscopy (FTIR) study. The morphological characterisations were carried out by the Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). To characterize the prepared nanocomposites electrode, a cyclic voltammetry test for measuring specific capacitance, and an impedance test were conducted. The highest value of specific capacitance obtained for the TiO2 coated MWCNTs/PANI nanocomposite was 443.57 F/g at 2 mV/s scan rate. Upon addition of graphene nanosheet to the TiO2 coated MWCNTs in a weight ratio of (9:1) the specific capacitance value increased to 666.3 F/g at the same scan rate, also resulting in an increase in energy density and power density.展开更多
Based on dislocation theory, we investigate the mechanism of strain rate effect. Strain rate effect and dislocation motion are bridged by Orowan＇s relationship, and the stress dependence of dislocation velocity is co...Based on dislocation theory, we investigate the mechanism of strain rate effect. Strain rate effect and dislocation motion are bridged by Orowan＇s relationship, and the stress dependence of dislocation velocity is considered as the dynamics relationship of dislocation motion. The mechanism of strain rate effect is then investigated qualitatively by using these two relationships although the kinematics relationship of dislocation motion is absent due to complicated styles of dislocation motion. The process of strain rate effect is interpreted and some details of strain rate effect are adequately discussed. The present analyses agree with the existing experimental results. Based on the analyses, we propose that strain rate criteria rather than stress criteria should be satisfied when a metal is fully yielded at a given strain rate.展开更多
Desktop 3D printers have revolutionized how designers and makers prototype and manufacture certain products.Highly popular fuse deposition modeling(FDM)desktop printers have enabled a shift to low-cost consumer goods ...Desktop 3D printers have revolutionized how designers and makers prototype and manufacture certain products.Highly popular fuse deposition modeling(FDM)desktop printers have enabled a shift to low-cost consumer goods markets,through reduced capital equipment investment and consumable material costs.However,with this drive to reduce costs,the computer numerical control(CNC)systems implemented in FDM printers are often compromised by poor accuracy and contouring errors.This condition is most critical as users begin to use 3D-printed components in load-bearing applications or to perform mechanical functions.Improved methods of low-cost 3D printer calibration are needed before their open-design potential can be realized in applications,including 3D-printed orthotics and prosthetics.This paper applies methodologies associated with high-precision CNC machining systems,namely,kinematic error modeling and compensation coupled with standardized test methods from ISO230-4,such as the ballbar for kinematic and dynamic error measurements,to examine the influence and feasibility for use on low-cost CNC/3D printing platforms.Recently,the U.S.Food and Drug Administration's"Technical considerations for additive manufactured medical devices"highlighted the need to develop standards specific to additive manufacturing in regulated manufacturing environments.This paper shows the benefits of the methods described within ISO230-4 for error assessment,alongside applying kinematic error modeling and compensation to the popular kinematic configuration of an Ultimaker 3D printer.A Renishaw ballbar QC10 is used to quantify the Ultimaker's errors and thereby populate the error model.This method quantifies machine errors and populates these in a mathematical model of the CNC system.Then,a post-processor can be used to compensate the printing code.Subsequently,the ballbar is used to demonstrate the dramatic impact of the error compensation model on the accuracy and contouring of the Ultimaker printer with 58%reduction in overall circularity error and 90%reduction in squareness error.展开更多
The Lonversion of polyacrylonitrile(PAN)fibre to carbon fibre consists of an oxidative stabili-zation process in which the PAN fibre is heated between 200-300℃ in air to give a thermally co-herent structure.The struc...The Lonversion of polyacrylonitrile(PAN)fibre to carbon fibre consists of an oxidative stabili-zation process in which the PAN fibre is heated between 200-300℃ in air to give a thermally co-herent structure.The structural changes of PAN fibres during stabilization have been investigatedusing Fourier Transform Infrared Spectroscopy(FTIR)and Differential Scanning Calorimetry(DSC).An attempt has also been made to follow the conversion of the structure using Ramanspectroscopy as a complementary technique.The FTIR spectra of the fibres subjected to variousdegree of heat treatment show a continuous decrease in nitrile absorption and a simultaneous in-crease in intensity of the C=N and/or C=C bands as the stabilization proceeds.A conversion ra-tio(CR)is defined as the intensity of the C=N and/or C=C bands relative to that of the nitrilegroups.The exotherm present in the DSC experiments was observed to weaken progressively dur-ing the stabilization process.It is confirmed that the original PAN structure is dissipating and thenew ladder polymer is being formed.展开更多
This study reports the variation of residual strains within the posterior ventral area of the Ensis siliqua mollusc shell, as determined using glancing incidence synchrotron X-ray diffraction. The outer layer of this ...This study reports the variation of residual strains within the posterior ventral area of the Ensis siliqua mollusc shell, as determined using glancing incidence synchrotron X-ray diffraction. The outer layer of this structure exhibits a tensile strain, in contrast to a compressive strain observed within the inner layer. Fluctuations in unit cell parameters for the inner layer have been determined, showing that the microscopic prismatic layer of the structure exhibits a compressive strain orientated parallel to the surface of the shell. This is thought to enhance the crack deflection properties of this layer, and aid in resisting catastrophic failure. Further analysis of residual strains has been performed using the same method, throughout several stages of compressive testing of the anterior dorsal region of the shell. This identified no variation in residual strains at various levels of loading, and it is therefore proposed that load may be transferred via the organic matrix of mollusc shell structures. A Raman spectroscopic investigation, comparing whole and powdered shell with non-biogenic aragonite, has shown that residual strains are also present in this analagous material which is devoid of organic content. This indicates that the observed strain is not entirely due to the organic matrix.展开更多
文摘We use dislocation theory and molecular dynamics （MD） simulations to investigate the effect of atom properties on the macroscopic strain rate sensitivity of f cc metals. A method to analyse such effect is proposed. The stress dependence of dislocation velocity is identified as the key of such study and is obtained via 2-D MD simulations on the motion of an individual dislocation in an fcc metal. Combining the simulation results with Orowan＇s relationship, it is concluded that strain rate sensitivities of fcc metals are mainly dependent on their atomic mass rather than the interatomic potential. The order of strain rate sensitivities of five fcc metals obtained by analysing is consistent with the experimental results available.
文摘Wear is a prevalent issue across various industries. Spherical fused tungsten carbide (sFTC) reinforced nickel-aluminum bronze (NAB) matrix composite surface deposits have shown remarkable potential in mitigating wear by approximately 80%. However, the performance of these sFTC/NAB composite surface deposits is determined by their residual stress state, and the precise macroscopic and microscopic residual stresses within these composites have yet to be clearly established. To address this gap, we employed neutron diffraction to measure the residual stresses in the sFTC/NAB composite surface deposits and re-melted NAB samples produced via laser melt injection. Significant residual stresses were determined. The maximum tensile macro residual stress appears approximately 1-1.5 mm below the composite layer. Residual stresses accumulate with an increasing number of laser process tracks. The maximum tensile macro residual stress in the three-track samples reaches about 350 MPa. Preheating the base plate significantly reduces the levels of macroscopic residual stress. The WC phase displayed significant compressive thermal misfit residual stress magnitude, while the Cu matrix exhibited tensile thermal misfit residual stress. Preheating the base plate does not reduce microscopic thermal misfit residual stress levels. In addition, a finite element model was built to investigate temperature and residual stresses in the re-melted NAB samples. The predicted temperature history and residual stress agree with the experimental results.
基金the Chinese Foundation Research ProjectionMagnesium Elektron Ltd. and the Manchester Materials Science Center of University of Manchester.
文摘The current research and development of magnesium alloys is summarized. Several aspects of magnesium alloys are described： cast Mg alloy, wrought Mg alloy, and novel processing. The subjects are discussed individually and recommendations for further study are listed in the final section.
基金supported financially by the National Key R&D Program of China (No. 2017YFB0703104)the National Natural Science Foundation of China (No. 51401219)
文摘The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled hierarchical multiscale modeling methods. Measurements showed that the macroscopic and total RSes had the largest variations in the longitudinal direction(LD). Increasing the welding speed led to higher values of measured LD macroscopic and total RSes in the matrix. The welding speed also significantly influenced the distributions and magnitudes of the microscopic RSes. The RSes were predicted via an improved hierarchical multiscale model, which includes a constant coefficient of friction based thermal model. The RSes in the composite plates before friction stir welding(FSW) were computed and then set as the initial states of the FSW process during modeling. This improved decoupled multiscale model provided improved predictions of the temperature and RSes compared with our previous model.
基金the National Key R&D Program of China(No.2017YFB0703104)the National Natural Science Foundation of China(Nos.51871214 and 51931009)the“Key Research Program of Frontier Sciences,CAS”(No.QYZDJ-SSWJSC015)。
文摘One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites(CNT/Al)composites is the load transfer strengthening mechanism(LTSM).However,a fundamental issue concerning the LTSM is that quantitative measurements of load partitioning in these composites during loading are very limited.In this study,in-situ neutron diffraction study on the tensile deformation of the 3 vol.%CNT/2009 Al composite and the unreinforced 2009 Al alloy was conducted.The{311}and{220}diffraction elastic constants(DECs)of the 2009 Al alloy were determined.Using those DECs the average stress in the 2009 Al matrix of the composite was calculated.Then the average stress in the CNTs was separated by using the stress equilibrium condition.Computational homogenization models were also applied to explain the stress evolution in each phase.Predicted results agree with experimental data.In the present case,the average stress in the CNTs reaches 1630 MPa at the yield strength of the composite based on linear regression of the measured data,which leads to an increment of yield strength by about 37 MPa.As the result of this work,an approach to quantify load partitioning in the CNTs is developed for the CNT/Al composites,which can be applied to optimize the mechanical properties of the composites.
文摘An investigation was carried out to modify the toughness of triethylene tetramine cured DGEBA （diglycidyl ether of bisphenol-A） resin using solid amine terminated poly （ethylene glycol） benzoate （ATPEGB） as modifier with and without red mud waste particles. The solid ATPEGB modifier synthesized from the acid catalyzed esterification reaction of poly （ethylene glycol） （PEG） and 4-amino benzoic acid was characterized by Fourier transform infrared spectroscopy （FT-IR） and ^1H-NMR （nuclear magnetic resonance） spectroscopies, viscosity measurements, and solubility parameter calculation. The unfilled and red mud waste filled modified epoxy networks were evaluated with impact, adhesive, tensile, flexural and thermal properties by differential scanning calorimetry （DSC）, thermogravimetric （TG） and dynamic mechanical analysis （DMA）. The effect of modifier concentration and red mud waste particles on toughening behavior was also investigated. The optimum properties were obtained at 12.5 phr （parts per hundred parts of resin） concentration of the modifier. The ATPEGB modified cured epoxy was thermally stable up to 315℃. The morphology on fracture surfaces of cured epoxy was also analyzed by scanning electron microscopy （SEM）.
基金financially supported by the National Natural Science Foundation of China (Nos. 51871076, 51671070, 51827801, 51671067, and 51671071)the Opening Funding of the State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, China (No. AWJ-Z16-02)the Chinese Scholarship Council (CSC) and the German Science Foundation (DFG) (Nos. PA 2275/2-1, PA 2275/4-1, and PA 2275/6-1)
文摘N^+ ion irradiation is utilized to tune the structure and mechanical properties of a Cu48Zr47.2Al4Nb0.8 bulk metallic glass composite(BMGC). Ion irradiation increases the disorder near the surface, as probed by neutron diffraction, and, moreover, causes the phase transformation from B2Cu Zr to B19’ CuZr martensitic phase in the studied BMGC. The tensile plasticity of the BMGC is dramatically improved after ion irradiation, which results from multiple shear banding on the surface and the martensitic transformation of the B2 to B19’ Cu Zr martensitic phase. The experimental results are strongly corroborated by complementary molecular dynamic simulations.
文摘A statistical approach is developed, based on a Monte Carlo method, in order to determine the statistical composition of a polyamide-6 sample composed of caprolactam （an AB-type monomer） and of a di-acid （A2 type） or a tri- acid （A3 type） as coupling agents. For this composition, the linear theological behavior of these systems is predicted using a tube-based theory. This allows us to show that while coupling agents of type A2 can be seen as flow improver, the effect of branching agents of type A3, depending on the synthesis recipe and the conversion level, can lead either to an increase or to a decrease of the viscosity. By adding specific amount of these agents, we also show that it is possible to obtain materials with the same zero-shear viscosity but with different shear thinning behavior. Furthermore, the polydispersity of linear samples of the same average number molecular weight, Mn, is discussed in function of the amount of A2 monomers they contain. Ranging from 2 to 1.5, this difference in polydispersity is expected to have a significant influence on the processing behavior of such materials.
文摘This paper reports that InAs/In0.53Ga0.47As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current density of 3kA/cm^2 has been obtained for diodes with AlAs barriers of ten monolayers, and an Ino.53Ga0.47As well of eight monolayers with four monolayers of InAs insert layer. The effects of growth interruption for smoothing potential barrier interfaces have been investigated by high resolution transmission electron microscope.
文摘Hybrid proton conducting membranes of poly（vinyl alcohol） （PVA） and phosphomolybdic acid （PMA） were prepared by solution casting method. The effect of PMA doping and PVA crosslinking density on the membrane properties and proton conductivity were investigated. The crosslinking reaction between the hydroxyl group of PVA and the aldehyde group of glutaraldehyde （GA） was characterized by IR spectroscopy. Proton conductivity of the membranes increases with an increase in concentration of the doped PMA and also with an increase in crosslinking density of the membranes. Proton conductivity results indicate that a significant amount of PMA was maintained in the membranes even after several hours of immersion in water. A maximum conductivity of 0.0101 S cm^-1 was obtained for the membrane with 33.3 wt% PMA and crosslinking density of 5.825 mol%. X-ray diffraction studies were carried out to investigate the influence of PMA doping and crosslinking density on the nature of the membranes. These properties make them very good candidates for polymer electrolyte membranes for direct methanol fuel cell application.
基金support from the National Key R&D Program of China(2020YFD0900900)Science and Technology Planning Project of Zhoushan of China(2022C41001)Zhejiang Ocean University(11135091221)。
文摘Low-value,renewable,carbon-rich resources,with different biomass feedstocks and their derivatives as typical examples,represent virtually inexhaustive carbon sources and carbon-related energy on Earth.Upon conversion to higher-value forms(referred to as“up-carbonization”here),these abundant feedstocks provide viable opportunities for energy-rich fuels and sustainable platform chemicals production.However,many of the current methods for such up-carbonization still lack sufficient energy,cost,and material efficiency,which affect their economics and carbon-emissions footprint.With external electricity precisely delivered,discharge plasmas enable many stubborn reactions to occur under mild conditions,by creating locally intensified and highly reactive environments.This technology emerges as a novel,versatile technology platform for integrated or stand-alone conversion of carbon-rich resources.The plasma-based processes are compatible for integration with increasingly abundant and cost-effective renewable electricity,making the whole conversion carbon-neutral and further paving the plasma-electrified upcarbonization to be performance-,environment-,and economics-viable.Despite the chief interest in this emerging area,no review article brings together the state-of-the-art results from diverse disciplines and underlies basic mechanisms and chemistry underpinned.As such,this review aims to fill this gap and provide basic guidelines for future research and transformation,by providing an overview of the application of plasma techniques for carbon-rich resource conversion,with particular focus on the perspective of discharge plasmas,the fundamentals of why plasmas are particularly suited for upcarbonization,and featured examples of plasma-enabled resource valorization.With parallels drawn and specificity highlighted,we also discuss the technique shortcomings,current challenges,and research needs for future work.
文摘Graphene, an extraordinary allotropy of carbon, the 2D nanosheet, have been synthesized through exfoliation of graphite in ortho dichloro benzene by sonication. The morphological changes in different interval of sonication have been investigated by Scanning Electron Microscopy (SEM) andTransmission Electron Microscopy (TEM). Raman Spectra confirmed the formation of defect free Graphene sheets. As prepared Graphene showed high thermal stability under N2 atmosphere. It has been observed that sonication for 4 hours, effectively exfoliates graphite to form Graphene sheets. However, further sonication leads to restacking of Graphene sheets. The formation of Graphene is supposed to be due to the Sonopolymerization of the solvent (ortho-dichloro benzene)and graphite solvent interaction.
文摘Nowadays with ever increasing demand of energy, developing of alternative power sources is an important issue all over the world. In this respect we have prepared nanocomposites based on metal oxide (titanium oxide) coated multiwalled carbon nanotubes (MWCNTs)/polyaniline (PANI) with graphene and without graphene and studied their electrochemical performance. The formation of the polymer in the nanocomposites was confirmed by the Fourier Transform Infrared Spectroscopy (FTIR) study. The morphological characterisations were carried out by the Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). To characterize the prepared nanocomposites electrode, a cyclic voltammetry test for measuring specific capacitance, and an impedance test were conducted. The highest value of specific capacitance obtained for the TiO2 coated MWCNTs/PANI nanocomposite was 443.57 F/g at 2 mV/s scan rate. Upon addition of graphene nanosheet to the TiO2 coated MWCNTs in a weight ratio of (9:1) the specific capacitance value increased to 666.3 F/g at the same scan rate, also resulting in an increase in energy density and power density.
文摘Based on dislocation theory, we investigate the mechanism of strain rate effect. Strain rate effect and dislocation motion are bridged by Orowan＇s relationship, and the stress dependence of dislocation velocity is considered as the dynamics relationship of dislocation motion. The mechanism of strain rate effect is then investigated qualitatively by using these two relationships although the kinematics relationship of dislocation motion is absent due to complicated styles of dislocation motion. The process of strain rate effect is interpreted and some details of strain rate effect are adequately discussed. The present analyses agree with the existing experimental results. Based on the analyses, we propose that strain rate criteria rather than stress criteria should be satisfied when a metal is fully yielded at a given strain rate.
基金supported by Science Foundation Ireland through the I-Form Advanced Manufacturing Research Centre 16/RC/3872
文摘Desktop 3D printers have revolutionized how designers and makers prototype and manufacture certain products.Highly popular fuse deposition modeling(FDM)desktop printers have enabled a shift to low-cost consumer goods markets,through reduced capital equipment investment and consumable material costs.However,with this drive to reduce costs,the computer numerical control(CNC)systems implemented in FDM printers are often compromised by poor accuracy and contouring errors.This condition is most critical as users begin to use 3D-printed components in load-bearing applications or to perform mechanical functions.Improved methods of low-cost 3D printer calibration are needed before their open-design potential can be realized in applications,including 3D-printed orthotics and prosthetics.This paper applies methodologies associated with high-precision CNC machining systems,namely,kinematic error modeling and compensation coupled with standardized test methods from ISO230-4,such as the ballbar for kinematic and dynamic error measurements,to examine the influence and feasibility for use on low-cost CNC/3D printing platforms.Recently,the U.S.Food and Drug Administration's"Technical considerations for additive manufactured medical devices"highlighted the need to develop standards specific to additive manufacturing in regulated manufacturing environments.This paper shows the benefits of the methods described within ISO230-4 for error assessment,alongside applying kinematic error modeling and compensation to the popular kinematic configuration of an Ultimaker 3D printer.A Renishaw ballbar QC10 is used to quantify the Ultimaker's errors and thereby populate the error model.This method quantifies machine errors and populates these in a mathematical model of the CNC system.Then,a post-processor can be used to compensate the printing code.Subsequently,the ballbar is used to demonstrate the dramatic impact of the error compensation model on the accuracy and contouring of the Ultimaker printer with 58%reduction in overall circularity error and 90%reduction in squareness error.
文摘The Lonversion of polyacrylonitrile(PAN)fibre to carbon fibre consists of an oxidative stabili-zation process in which the PAN fibre is heated between 200-300℃ in air to give a thermally co-herent structure.The structural changes of PAN fibres during stabilization have been investigatedusing Fourier Transform Infrared Spectroscopy(FTIR)and Differential Scanning Calorimetry(DSC).An attempt has also been made to follow the conversion of the structure using Ramanspectroscopy as a complementary technique.The FTIR spectra of the fibres subjected to variousdegree of heat treatment show a continuous decrease in nitrile absorption and a simultaneous in-crease in intensity of the C=N and/or C=C bands as the stabilization proceeds.A conversion ra-tio(CR)is defined as the intensity of the C=N and/or C=C bands relative to that of the nitrilegroups.The exotherm present in the DSC experiments was observed to weaken progressively dur-ing the stabilization process.It is confirmed that the original PAN structure is dissipating and thenew ladder polymer is being formed.
文摘This study reports the variation of residual strains within the posterior ventral area of the Ensis siliqua mollusc shell, as determined using glancing incidence synchrotron X-ray diffraction. The outer layer of this structure exhibits a tensile strain, in contrast to a compressive strain observed within the inner layer. Fluctuations in unit cell parameters for the inner layer have been determined, showing that the microscopic prismatic layer of the structure exhibits a compressive strain orientated parallel to the surface of the shell. This is thought to enhance the crack deflection properties of this layer, and aid in resisting catastrophic failure. Further analysis of residual strains has been performed using the same method, throughout several stages of compressive testing of the anterior dorsal region of the shell. This identified no variation in residual strains at various levels of loading, and it is therefore proposed that load may be transferred via the organic matrix of mollusc shell structures. A Raman spectroscopic investigation, comparing whole and powdered shell with non-biogenic aragonite, has shown that residual strains are also present in this analagous material which is devoid of organic content. This indicates that the observed strain is not entirely due to the organic matrix.
