It is a challenge to polish the interior surface of an additively manufactured component with complex structures and groove sizes less than 1 mm.Traditional polishing methods are disabled to polish the component,meanw...It is a challenge to polish the interior surface of an additively manufactured component with complex structures and groove sizes less than 1 mm.Traditional polishing methods are disabled to polish the component,meanwhile keeping the structure intact.To overcome this challenge,small-grooved components made of aluminum alloy with sizes less than 1 mm were fabricated by a custom-made printer.A novel approach to multi-phase jet(MPJ)polishing is proposed,utilizing a self-developed polisher that incorporates solid,liquid,and gas phases.In contrast,abrasive air jet(AAJ)polishing is recommended,employing a customized polisher that combines solid and gas phases.After jet polishing,surface roughness(Sa)on the interior surface of grooves decreases from pristine 8.596μm to 0.701μm and 0.336μm via AAJ polishing and MPJ polishing,respectively,and Sa reduces 92%and 96%,correspondingly.Furthermore,a formula defining the relationship between linear energy density and unit defect volume has been developed.The optimized parameters in additive manufacturing are that linear energy density varies from 0.135 J mm^(-1)to 0.22 J mm^(-1).The unit area defect volume achieved via the optimized parameters decreases to 1/12 of that achieved via non-optimized ones.Computational fluid dynamics simulation results reveal that material is removed by shear stress,and the alumina abrasives experience multiple collisions with the defects on the heat pipe groove,resulting in uniform material removal.This is in good agreement with the experimental results.The novel proposed setups,approach,and findings provide new insights into manufacturing complex-structured components,polishing the small-grooved structure,and keeping it unbroken.展开更多
Titanium alloys are excellent structural materials in engineering fields,but their poor tribological properties limit their further applications.Electroless plating is an effective method to enhance the tribological p...Titanium alloys are excellent structural materials in engineering fields,but their poor tribological properties limit their further applications.Electroless plating is an effective method to enhance the tribological performance of alloys,but it is difficult to efficiently apply to titanium alloys,due to titanium alloy’s strong chemical activity.In this work,the electroless Nickel-Boron(Ni-B)coating was successfully deposited on the surface of titanium alloy(Ti-6AL-4V)via a new pre-treatment process.Then,linearly reciprocating sliding wear tests were performed to evaluate the tribological behaviors of titanium alloy and its electroless Ni-B coatings.It was found that the Ni-B coatings can decrease the wear rate of the titanium alloy from 19.89×10^(−3)mm^(3)to 0.41×10^(−3)mm^(3),which attributes to the much higher hardness of Ni-B coatings.After heat treatment,the hardness of Ni-B coating further increases corresponding to coating crystallization and hard phase formation.However,heat treatment does not improve the tribological performance of Ni-B coating,due to the fact that higher brittleness and more severe oxidative wear exacerbate the damage of heat-treated coatings.Furthermore,the Ni-B coatings heat-treated both in air and nitrogen almost present the same tribological performance.The finding of this work on electroless coating would further extend the practical applications of titanium alloys in the engineering fields.展开更多
Small-scale electromagnetic soft actuators are characterized by a fast response and simplecontrol,holding prospects in the field of soft and miniaturized robotics.The use of liquid metal(LM)to replace a rigid conducto...Small-scale electromagnetic soft actuators are characterized by a fast response and simplecontrol,holding prospects in the field of soft and miniaturized robotics.The use of liquid metal(LM)to replace a rigid conductor inside soft actuators can reduce the rigidity and enhance the actuation performance and robustness.Despite research efforts,challenges persist in the flexible fabrication of LM soft actuators and in the improvement of actuation performance.To address these challenges,we developed a fast and robust electromagnetic soft microplate actuator based on a laser-induced selective adhesion transfer method.Equipped with unprecedentedly thin LM circuit and customized low Young’s modulus silicone rubber(1.03 kPa),our actuator exhibits an excellent deformation angle(265.25?)and actuation bending angular velocity(284.66 rad·s^(-1)).Furthermore,multiple actuators have been combined to build an artificial gripper with a wide range of functionalities.Our actuator presents new possibilities for designing small-scaleartificial machines and supports advancements in ultrafast soft and miniaturized robotics.展开更多
Split Hopkinson pressure bar (SHPB) has become a frequently used technique to measure the uniaxial compressive stress-strain relation of various engineering materials at high strain-rates. The accuracy of an SHPB test...Split Hopkinson pressure bar (SHPB) has become a frequently used technique to measure the uniaxial compressive stress-strain relation of various engineering materials at high strain-rates. The accuracy of an SHPB test is based on the assumption of uniaxial and uniform stress distribution within the specimen, which, however, is not always satisfied in an actual SHPB test due to the existence of some unavoidable negative factors, e.g., interface friction constrains. Kinetic interface friction tests based on a simple device for engineering materials testing on SHPB tests are performed. A kinetic interface friction model is proposed and validated by implementing it into a numerical model. It shows that the proposed simple device is sufficient to obtain kinetic interface friction results for common SHPB tests. The kinetic friction model should be used instead of the frequently used constant friction model for more accurate numerical simulation of SHPB tests.展开更多
The mechanical and wear properties of CFRP laminate were investigated using a method of cycling low velocity impact, to study the trend and mechanism of impact resistance of the CFRP laminate under repeated impact dur...The mechanical and wear properties of CFRP laminate were investigated using a method of cycling low velocity impact, to study the trend and mechanism of impact resistance of the CFRP laminate under repeated impact during its service process. The interface responses of CFRP laminate under di erent impact kinetic energy during the cycling impact process were studied were studied experimentally, such as impact contact duration, deformation and energy absorption. The worn surface morphologies were observed through optical microscopy and a 3?D surface profiler and the cross?sectional morphologies were observed through SEM to investigate the mechanism of impact material dam?age. Based on a single?degree?of?freedom damping vibration model, the normal contact sti ness and contact damp?ing of the material in di erent wear stages were calculated. It shows the failure process of CFRP laminate damaged by accumulated absorption energy under the cycling impact of di erent initial kinetic energy. The results indicate that the sti ness and damping coe cients will change at di erent impact velocities or cycle numbers. The damage mechanism of CFRP laminates under cycling low kinetic energy is delamination. After repeated experiments, it was found that there was a threshold value for the accumulated absorption energy before the failure of the CFRP laminate.展开更多
The present work employed the X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, and electron probe microanalysis techniques to identify the microstructural evolution and mechanical a...The present work employed the X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, and electron probe microanalysis techniques to identify the microstructural evolution and mechanical and abrasive behavior of high carbon steel during quenching-partitioning treatment with an aim to enhance the toughness and wear resistance of high carbon steel.Results showed that, with the increase in partitioning temperature from 250 to 400℃, the amount of retained austenite(RA) decreased resulting from the carbide precipitation effect after longer partitioning times.Moreover, the stability of RA generally increased because of the enhanced degree of carbon enrichment in RA.Given the factors affecting the toughness of high carbon steel, the stability of RA associated with size, carbon content, and morphology plays a significant role in determining the toughness of high carbon steel.The analysis of the wear resistance of samples with different mechanical properties shows that hardness is the primary factor affecting the wear resistance of high carbon steel, and the toughness is the secondary one.展开更多
The Issue of mixing efficiency in agitated tanks has drawn serious concern in many industrial processes. The turbulence model is very critical to predicting mixing process in agitated tanks. On the basis of computatio...The Issue of mixing efficiency in agitated tanks has drawn serious concern in many industrial processes. The turbulence model is very critical to predicting mixing process in agitated tanks. On the basis of computational fluid dynamics（CFD） software package Fluent 6.2, the mixing characteristics in a tank agitated by dual six-blade-Rushton-turbines（6-DT） are predicted using the detached eddy simulation（DES） method. A sliding mesh（SM） approach is adopted to solve the rotation of the impeller. The simulated flow patterns and liquid velocities in the agitated tank are verified by experimental data in the literature. The simulation results indicate that the DES method can obtain more flow details than Reynolds-averaged Navier-Stokes（RANS） model. Local and global mixing time in the agitated tank is predicted by solving a tracer concentration scalar transport equation. The simulated results show that feeding points have great influence on mixing process and mixing time. Mixing efficiency is the highest for the feeding point at location of midway of the two impellers. Two methods are used to determine global mixing time and get close result. Dimensionless global mixing time remains unchanged with increasing of impeller speed. Parallel, merging and diverging flow pattern form in the agitated tank, respectively, by changing the impeller spacing and clearance of lower impeller from the bottom of the tank. The global mixing time is the shortest for the merging flow, followed by diverging flow, and the longest for parallel flow. The research presents helpful references for design, optimization and scale-up of agitated tanks with multi-impeller.展开更多
In this paper, the numerical simulation on the flow field of a four-channel coal burner was investigated with Fluent software. The three-dimension model was created with UG software. The structure was meshed by using ...In this paper, the numerical simulation on the flow field of a four-channel coal burner was investigated with Fluent software. The three-dimension model was created with UG software. The structure was meshed by using Gambit software. The realizable K-ε turbulence model and simple method were adopted. The variation of the inner flow field of the burner was studied and analyzed. The results simulated to the burner by the realizable K-ε turbulence model show that the contours of theflowfield accord with the actual condition and the realizable K-ε model is proved to be feasible and the results of simulation are creditable. That will have important significance to the improvement of the structure and parameter optimization of the four-channel coal burner in the future.展开更多
The mechanical response of shock-loaded microelectromechanical systems (MEMS) is simulated to formulate guidelines for the design of dynamically reliable MEMS. MEMS are modeled as microstructures supported on elastic ...The mechanical response of shock-loaded microelectromechanical systems (MEMS) is simulated to formulate guidelines for the design of dynamically reliable MEMS. MEMS are modeled as microstructures supported on elastic substrates, and the shock loads are represented as pulses of acceleration applied by the package on the substrate over a finite time duration. For typical MEMS and shock loads, the response of the substrate is closely approximated by rigid-body motion. Results indicate that modeling the shock force as a quasi-static force for MEMS with low-natural frequencies may lead to erroneous results. A criterion is obtained to distinguish between the dynamic and quasi-static responses of the MEMS.展开更多
Versatile liquid manipulating surfaces combining patternable and controllable wettability have recently motivated considerable attention owing to their significant advantages in droplet-solid impacting behaviors,micro...Versatile liquid manipulating surfaces combining patternable and controllable wettability have recently motivated considerable attention owing to their significant advantages in droplet-solid impacting behaviors,microdroplet self-removal,and liquid–liquid interface reaction applications.However,developing a facile and efficient method to fabricate these versatile surfaces remains an enormous challenge.In this paper,a strategy for the fabrication of liquid manipulating surfaces with patternable and controllable wettability on Polyimide(PI)film based on femtosecond laser thermal accumulation engineering is proposed.Because of its controllable micro-/nanostructures and chemical composition through adjusting the local thermal accumulation,the wettability of PI film can be tuned from superhydrophilicity(~3.6°)to superhydrophobicity(~151.6°).Furthermore,three diverse surfaces with patternable and heterogeneous wettability were constructed and various applications were successfully realized,including water transport,droplet arrays,and liquid wells.This work may provide a facile strategy for achieving patternable and controllable wettability efficiently and developing multifunctional liquid steering surfaces.展开更多
Reinforcing fillers are of great importance in tribological performance and tribofilm formation of polymeric composites.In this study,the tribological properties of aramid particle(AP)and short carbon fiber(SCF)reinfo...Reinforcing fillers are of great importance in tribological performance and tribofilm formation of polymeric composites.In this study,the tribological properties of aramid particle(AP)and short carbon fiber(SCF)reinforced polyimide(PI)composites were added to hexagonal boron nitride(h-BN),and silica(SiO_(2))nanoparticles sliding against alumina were comprehensively investigated.When sliding occurred with AP-reinforced PI composites,the tribological properties were not closely depended on the pressure×velocity(p×v)factors and the nanoparticles.The interactions between AP and its counterpart could not induce tribo-sintering of the transferred wear debris.As such,the tribofilm seemed to be in a viscous state,leading to higher friction and wear.However,the inclusion of hard SCF into the PI matrix changed the interfacial interactions with alumina.A robust tribofilm consisting of a high fraction of silica was generated when the SCF-reinforced PI was added to the SiO_(2) nanoparticles.It exhibited a high load-carrying capability and was easily sheared.This caused a significant decrease in the friction and wear of the PI composite at 8 MPa·1m/s.Moreover,due to their high melting point,few h-BN nanoparticles were observed in the tribofilm of the SCF-reinforced PI when hexagonal boron nitride was added.展开更多
Defect evolution in a single crystal silicon which is implanted with hydrogen atoms and then annealed is investigated in the present paper by means of molecular dynamics simulation. By introducing defect density based...Defect evolution in a single crystal silicon which is implanted with hydrogen atoms and then annealed is investigated in the present paper by means of molecular dynamics simulation. By introducing defect density based on statistical average, this work aims to quantitatively examine defect nucleation and growth at nanoscale during annealing in Smart-Cut technology. Research focus is put on the effects of the implantation energy, hydrogen implantation dose and annealing temperature on defect density in the statistical region. It is found that most de- fects nucleate and grow at the annealing stage, and that defect density increases with the increase of the annealing temperature and the decrease of the hydrogen implantation dose. In addition, the enhancement and the impediment effects of stress field on defect density in the annealing process are discussed.展开更多
Tribology behaviors of energetic crystals play critical roles in the friction-induced hotspot in highenergy explosive,however,the binder and energetic crystals are not distinguished properly in previous investigations...Tribology behaviors of energetic crystals play critical roles in the friction-induced hotspot in highenergy explosive,however,the binder and energetic crystals are not distinguished properly in previous investigations.In this study,for the first time,the nanoscale friction ofβ-octahydro-1,3,5,7-tetranitro1,3,5,7-tetrazocine(β-HMX)crystal is studied with nanoscratch tests under the ramping load mode.The results show that the nanoscale friction and wear ofβ-HMX crystal,as a typical energetic material,is highly depended on the applied load.The friction coefficient ofβ-HMX crystal is initially high when no discernible wear is observed,and then it decreases to a stable value which varies from~0.2 to~0.7,depending on the applied load,scratch direction,and crystal planes.Theβ-HMX(011)surfaces show weakly friction and wear anisotropy behavior;in contrast,theβ-HMX(110)surfaces show strongly friction and wear anisotropy behavior where the friction coefficient,critical load for the elastic–plastic deformation transition and plastic–cracking deformation transition,and deformation index at higher normal load are highly depended on the scratch directions.Further analyses indicate the slip system and direction ofβ-HMX surfaces play key roles in determining the nanoscale friction and wear ofβ-HMX surfaces.The obtained results can provide deeper insight into the friction and wear of energetic crystal materials.展开更多
High-performance devices usually have curved surfaces, requiring high accuracy of shape and low surface roughness. It is a challenge to achieve high accuracies for form and position on a device with low surface roughn...High-performance devices usually have curved surfaces, requiring high accuracy of shape and low surface roughness. It is a challenge to achieve high accuracies for form and position on a device with low surface roughness. However, due to the unique nonlinear rheology, magnetorheological fluids with hard abrasives are widely applied in ultra-precision surface finishing. Compared with conventional mechanical finishing, magnetorheological finishing displays obviously advantages, such as high precision shape of machined surface, low surface roughness and subsurface damage, and easy control for finishing processes. However, finishing performance depends on various factors, e.g. volume fraction and distribution of magnetic particles, types of hard abrasives and additives, strength of magnetic field, finishing forms. Therefore, a comprehensive review on related works is essential to understand the state-of-the-art of magnetorheological finishing and beneficial to inspire researchers to develop lower cost, higher machining accuracy and efficient approaches and setups, which demonstrates a significant guidance for development of high-performance parts in fields of aerospace, navigation and clinical medicine etc. This review starts from the rheological property of magnetorheological fluids, summarizing dynamically nonlinear rheological properties and stable finishing approaches. Then, the effect of components in magnetorheological fluids is discussed on finishing performance, consisting of magnetic particles, carrier fluid, additives and abrasives. Reasonable configuration of magnetorheological fluids, and different magnetorheological finishing methods are presented for variously curved surfaces. In addition, the current finishing forms and future directions are also addressed in this review.展开更多
Processing(grinding,polishing)of phosphate laser(PL)glass involves material removal at two vastly different(spatial)scales.In this study,the nano‐and macro‐tribological properties of PL glass are investigated by rub...Processing(grinding,polishing)of phosphate laser(PL)glass involves material removal at two vastly different(spatial)scales.In this study,the nano‐and macro‐tribological properties of PL glass are investigated by rubbing the glass against a SiO_(2) counter‐surface in both dry and humid conditions.The results indicate that the friction of the PL glass/SiO_(2) pair has opposing trends at the nano‐and macroscales.At the nanoscale,the friction coefficient(COF)in humid air is much higher than in dry air,which is attributed to the capillary effect of the absorbed water‐film at the interface.At the macroscale,on the other hand,the COF in humid air is lower than in dry air,because the water‐related mechanochemical wear makes the worn surface less susceptible to cracking.Material removal for PL glass is better facilitated by humid air than by dry air at both scales,because the stress‐enhanced hydrolysis accelerates the material‐removal process in glass.Moreover,the material‐removal is more sensitive to contact pressure at the macroscale,because stronger mechanical‐interaction occurs during material removal at the macroscale with the multi asperity contact mode.At the macroscale,the material removal is more sensitive to contact pressure in humid air compared to dry air.Because almost all mechanical energy is used to remove material in humid air,and most of the mechanical energy is used to produce cracks in PL glass in dry air.The results of this study can help optimize the multi‐scale surface processing of optical glasses.展开更多
A high-throughput approach based on magnetron co-sputtering of alloy libraries is employed to investigate mechanical properties of crystalline and amorphous alloys in a ternary palladium(Pd)-tungsten(W)-silicon(Si)sys...A high-throughput approach based on magnetron co-sputtering of alloy libraries is employed to investigate mechanical properties of crystalline and amorphous alloys in a ternary palladium(Pd)-tungsten(W)-silicon(Si)system with the aim to reveal the difference in plastic deformation response and extract the relevant structure-property relationships of the alloys in the system.It was found that in contrast to crystalline alloys,the amorphous ones,i.e.,metallic glasses,exhibited a much smaller fluctuation range in the plasticity parameters(Er2/H and Wp/Wt),indicating a significant difference in the plastic deformation mechanism controlling the mechanical properties for the respective alloys.We propose that the inhomogeneous deformation of amorphous alloys localized in thin shear bands is responsible for the weaker compositional dependence of both plasticity parameters,while dislocation gliding in crystalline materials is significantly more dependent on the exact structure,thus resulting in a larger scattering range.Based on the representative efficient cluster packing model,a set of composition-dependent atomic structural models is proposed to figure out the structure-property relationships of amorphous alloys in Pd-W-Si alloy system.展开更多
Micro-robots have the characteristics of small size,light weight and flexible movement.To design a micro three-legged crawling robot with multiple motion directions,a novel driving scheme based on the inverse piezoele...Micro-robots have the characteristics of small size,light weight and flexible movement.To design a micro three-legged crawling robot with multiple motion directions,a novel driving scheme based on the inverse piezoelectric effect of piezoelectric ceramics was proposed.The three legs of the robot were equipped with piezoelectric bimorphs as drivers,respectively.The motion principles were analyzed and the overall force analysis was carried out with the theoretical mechanics method.The natural frequency,mode shape and amplitude were analyzed with simulation software COMSOL Multiphysics,the optimal size was determined through parametric analysis,and then the micro three-legged crawling robot was manufactured.The effects of different driving voltages,different driving frequencies,different motion bases and different loads on the motion speed of the robot were tested.It is shown that the maximum speed of single-leg driving was 35.41 cm/s,the switching ability between different motion directions was measured,and the movements in six different directions were achieved.It is demonstrated the feasibility of multi-directional motion of the structure.The research may provide a reference for the design and development of miniature piezoelectric three-legged crawling robots.展开更多
基金the National Key Research and Development Program of China(2018YFA0703400)the Young Scientists Fund of the National Natural Science Foundation of China(52205447)Changjiang Scholars Program of the Chinese Ministry of Education。
文摘It is a challenge to polish the interior surface of an additively manufactured component with complex structures and groove sizes less than 1 mm.Traditional polishing methods are disabled to polish the component,meanwhile keeping the structure intact.To overcome this challenge,small-grooved components made of aluminum alloy with sizes less than 1 mm were fabricated by a custom-made printer.A novel approach to multi-phase jet(MPJ)polishing is proposed,utilizing a self-developed polisher that incorporates solid,liquid,and gas phases.In contrast,abrasive air jet(AAJ)polishing is recommended,employing a customized polisher that combines solid and gas phases.After jet polishing,surface roughness(Sa)on the interior surface of grooves decreases from pristine 8.596μm to 0.701μm and 0.336μm via AAJ polishing and MPJ polishing,respectively,and Sa reduces 92%and 96%,correspondingly.Furthermore,a formula defining the relationship between linear energy density and unit defect volume has been developed.The optimized parameters in additive manufacturing are that linear energy density varies from 0.135 J mm^(-1)to 0.22 J mm^(-1).The unit area defect volume achieved via the optimized parameters decreases to 1/12 of that achieved via non-optimized ones.Computational fluid dynamics simulation results reveal that material is removed by shear stress,and the alumina abrasives experience multiple collisions with the defects on the heat pipe groove,resulting in uniform material removal.This is in good agreement with the experimental results.The novel proposed setups,approach,and findings provide new insights into manufacturing complex-structured components,polishing the small-grooved structure,and keeping it unbroken.
基金Supported by Sichuan Provincial Science and Technology Program of China(Grant No.2018JY0245)National Natural Science Foundation of China(Grant No.51975492)Natural Science Foundation of Southwest University of Science and Technology of China(Grant No.19xz7163).
文摘Titanium alloys are excellent structural materials in engineering fields,but their poor tribological properties limit their further applications.Electroless plating is an effective method to enhance the tribological performance of alloys,but it is difficult to efficiently apply to titanium alloys,due to titanium alloy’s strong chemical activity.In this work,the electroless Nickel-Boron(Ni-B)coating was successfully deposited on the surface of titanium alloy(Ti-6AL-4V)via a new pre-treatment process.Then,linearly reciprocating sliding wear tests were performed to evaluate the tribological behaviors of titanium alloy and its electroless Ni-B coatings.It was found that the Ni-B coatings can decrease the wear rate of the titanium alloy from 19.89×10^(−3)mm^(3)to 0.41×10^(−3)mm^(3),which attributes to the much higher hardness of Ni-B coatings.After heat treatment,the hardness of Ni-B coating further increases corresponding to coating crystallization and hard phase formation.However,heat treatment does not improve the tribological performance of Ni-B coating,due to the fact that higher brittleness and more severe oxidative wear exacerbate the damage of heat-treated coatings.Furthermore,the Ni-B coatings heat-treated both in air and nitrogen almost present the same tribological performance.The finding of this work on electroless coating would further extend the practical applications of titanium alloys in the engineering fields.
基金supported by the National Natural Science Foundation of China(Nos.52122511,61927814,and U20A20290)Anhui Provincial Natural Science Foundation(2308085QF218)+5 种基金China National Postdoctoral Program for Innovative Talents(BX20230351)China Postdoctoral Science Foundation(2023M733382)National Key R&D Program of China(2021YFF0502700)Major Scientific and Technological Projects in Anhui Province(202203a05020014)Fundamental Research Funds for the Central Universities(WK5290000003 and WK2090000058)Youth Innovation Promotion Association CAS(Y2021118)。
文摘Small-scale electromagnetic soft actuators are characterized by a fast response and simplecontrol,holding prospects in the field of soft and miniaturized robotics.The use of liquid metal(LM)to replace a rigid conductor inside soft actuators can reduce the rigidity and enhance the actuation performance and robustness.Despite research efforts,challenges persist in the flexible fabrication of LM soft actuators and in the improvement of actuation performance.To address these challenges,we developed a fast and robust electromagnetic soft microplate actuator based on a laser-induced selective adhesion transfer method.Equipped with unprecedentedly thin LM circuit and customized low Young’s modulus silicone rubber(1.03 kPa),our actuator exhibits an excellent deformation angle(265.25?)and actuation bending angular velocity(284.66 rad·s^(-1)).Furthermore,multiple actuators have been combined to build an artificial gripper with a wide range of functionalities.Our actuator presents new possibilities for designing small-scaleartificial machines and supports advancements in ultrafast soft and miniaturized robotics.
文摘Split Hopkinson pressure bar (SHPB) has become a frequently used technique to measure the uniaxial compressive stress-strain relation of various engineering materials at high strain-rates. The accuracy of an SHPB test is based on the assumption of uniaxial and uniform stress distribution within the specimen, which, however, is not always satisfied in an actual SHPB test due to the existence of some unavoidable negative factors, e.g., interface friction constrains. Kinetic interface friction tests based on a simple device for engineering materials testing on SHPB tests are performed. A kinetic interface friction model is proposed and validated by implementing it into a numerical model. It shows that the proposed simple device is sufficient to obtain kinetic interface friction results for common SHPB tests. The kinetic friction model should be used instead of the frequently used constant friction model for more accurate numerical simulation of SHPB tests.
基金National Natural Science Foundation of China(Grant Nos.U1530136,51627806)Young Scientific Innovation Team of Science and Technology of Sichuan Province of China(Grant No.2017TD0017)Opening Project of Key Laboratory of Testing Technology for Manufacturing Process of China(Grant Nos.2016-01,Southwest University of Science and Technology)
文摘The mechanical and wear properties of CFRP laminate were investigated using a method of cycling low velocity impact, to study the trend and mechanism of impact resistance of the CFRP laminate under repeated impact during its service process. The interface responses of CFRP laminate under di erent impact kinetic energy during the cycling impact process were studied were studied experimentally, such as impact contact duration, deformation and energy absorption. The worn surface morphologies were observed through optical microscopy and a 3?D surface profiler and the cross?sectional morphologies were observed through SEM to investigate the mechanism of impact material dam?age. Based on a single?degree?of?freedom damping vibration model, the normal contact sti ness and contact damp?ing of the material in di erent wear stages were calculated. It shows the failure process of CFRP laminate damaged by accumulated absorption energy under the cycling impact of di erent initial kinetic energy. The results indicate that the sti ness and damping coe cients will change at di erent impact velocities or cycle numbers. The damage mechanism of CFRP laminates under cycling low kinetic energy is delamination. After repeated experiments, it was found that there was a threshold value for the accumulated absorption energy before the failure of the CFRP laminate.
基金supported by the Natural Science Foundation of Southwest University of Science and Technology (No.19zx7163)the National Natural Science Foundation of China (No.51975492)。
文摘The present work employed the X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, and electron probe microanalysis techniques to identify the microstructural evolution and mechanical and abrasive behavior of high carbon steel during quenching-partitioning treatment with an aim to enhance the toughness and wear resistance of high carbon steel.Results showed that, with the increase in partitioning temperature from 250 to 400℃, the amount of retained austenite(RA) decreased resulting from the carbide precipitation effect after longer partitioning times.Moreover, the stability of RA generally increased because of the enhanced degree of carbon enrichment in RA.Given the factors affecting the toughness of high carbon steel, the stability of RA associated with size, carbon content, and morphology plays a significant role in determining the toughness of high carbon steel.The analysis of the wear resistance of samples with different mechanical properties shows that hardness is the primary factor affecting the wear resistance of high carbon steel, and the toughness is the secondary one.
基金Supported by Key Scientific Research Project of Sichuan Provincial Education Department(Grant No.15ZA0107)Doctor Foundation of Southwest University of Science and Technology(Grant No.11zx7162)
文摘The Issue of mixing efficiency in agitated tanks has drawn serious concern in many industrial processes. The turbulence model is very critical to predicting mixing process in agitated tanks. On the basis of computational fluid dynamics（CFD） software package Fluent 6.2, the mixing characteristics in a tank agitated by dual six-blade-Rushton-turbines（6-DT） are predicted using the detached eddy simulation（DES） method. A sliding mesh（SM） approach is adopted to solve the rotation of the impeller. The simulated flow patterns and liquid velocities in the agitated tank are verified by experimental data in the literature. The simulation results indicate that the DES method can obtain more flow details than Reynolds-averaged Navier-Stokes（RANS） model. Local and global mixing time in the agitated tank is predicted by solving a tracer concentration scalar transport equation. The simulated results show that feeding points have great influence on mixing process and mixing time. Mixing efficiency is the highest for the feeding point at location of midway of the two impellers. Two methods are used to determine global mixing time and get close result. Dimensionless global mixing time remains unchanged with increasing of impeller speed. Parallel, merging and diverging flow pattern form in the agitated tank, respectively, by changing the impeller spacing and clearance of lower impeller from the bottom of the tank. The global mixing time is the shortest for the merging flow, followed by diverging flow, and the longest for parallel flow. The research presents helpful references for design, optimization and scale-up of agitated tanks with multi-impeller.
文摘In this paper, the numerical simulation on the flow field of a four-channel coal burner was investigated with Fluent software. The three-dimension model was created with UG software. The structure was meshed by using Gambit software. The realizable K-ε turbulence model and simple method were adopted. The variation of the inner flow field of the burner was studied and analyzed. The results simulated to the burner by the realizable K-ε turbulence model show that the contours of theflowfield accord with the actual condition and the realizable K-ε model is proved to be feasible and the results of simulation are creditable. That will have important significance to the improvement of the structure and parameter optimization of the four-channel coal burner in the future.
文摘The mechanical response of shock-loaded microelectromechanical systems (MEMS) is simulated to formulate guidelines for the design of dynamically reliable MEMS. MEMS are modeled as microstructures supported on elastic substrates, and the shock loads are represented as pulses of acceleration applied by the package on the substrate over a finite time duration. For typical MEMS and shock loads, the response of the substrate is closely approximated by rigid-body motion. Results indicate that modeling the shock force as a quasi-static force for MEMS with low-natural frequencies may lead to erroneous results. A criterion is obtained to distinguish between the dynamic and quasi-static responses of the MEMS.
基金This research is supported by National Natural Science Foundation of China(Nos.52075557,51805553)Natural Science Foundation of Hunan Province(No.2021JJ20067)+1 种基金The Science and Technology Innovation Program of Hunan Province(No.2021RC3011)Open access funding provided by Shanghai Jiao Tong University
文摘Versatile liquid manipulating surfaces combining patternable and controllable wettability have recently motivated considerable attention owing to their significant advantages in droplet-solid impacting behaviors,microdroplet self-removal,and liquid–liquid interface reaction applications.However,developing a facile and efficient method to fabricate these versatile surfaces remains an enormous challenge.In this paper,a strategy for the fabrication of liquid manipulating surfaces with patternable and controllable wettability on Polyimide(PI)film based on femtosecond laser thermal accumulation engineering is proposed.Because of its controllable micro-/nanostructures and chemical composition through adjusting the local thermal accumulation,the wettability of PI film can be tuned from superhydrophilicity(~3.6°)to superhydrophobicity(~151.6°).Furthermore,three diverse surfaces with patternable and heterogeneous wettability were constructed and various applications were successfully realized,including water transport,droplet arrays,and liquid wells.This work may provide a facile strategy for achieving patternable and controllable wettability efficiently and developing multifunctional liquid steering surfaces.
基金The authors are grateful for the financial support received from National Natural Science Foundation of China(Grant Nos.51475446 and 51975492)the Research Foundation of Southwest University of Science and Technology(Grant Nos.18zx7162 and 18zx7125)Sichuan Science and Technology Program(Grant No.18YYJC0905).
文摘Reinforcing fillers are of great importance in tribological performance and tribofilm formation of polymeric composites.In this study,the tribological properties of aramid particle(AP)and short carbon fiber(SCF)reinforced polyimide(PI)composites were added to hexagonal boron nitride(h-BN),and silica(SiO_(2))nanoparticles sliding against alumina were comprehensively investigated.When sliding occurred with AP-reinforced PI composites,the tribological properties were not closely depended on the pressure×velocity(p×v)factors and the nanoparticles.The interactions between AP and its counterpart could not induce tribo-sintering of the transferred wear debris.As such,the tribofilm seemed to be in a viscous state,leading to higher friction and wear.However,the inclusion of hard SCF into the PI matrix changed the interfacial interactions with alumina.A robust tribofilm consisting of a high fraction of silica was generated when the SCF-reinforced PI was added to the SiO_(2) nanoparticles.It exhibited a high load-carrying capability and was easily sheared.This caused a significant decrease in the friction and wear of the PI composite at 8 MPa·1m/s.Moreover,due to their high melting point,few h-BN nanoparticles were observed in the tribofilm of the SCF-reinforced PI when hexagonal boron nitride was added.
基金Project supported by the National Natural Science Foundation of China(No.11372261)the Excellent Young Scientists Supporting Project of Science and Technology Department of Sichuan Province(No.2013JQ0030)+3 种基金the Supporting Project of Department of Education of Sichuan Province(No.2014zd3132)the Opening Project of Key Laboratory of Testing Technology for Manufacturing Process,Southwest University of Science and Technology-Ministry of Education(No.12zxzk02)the Fund of Doctoral Research of Southwest University of Science and Technology(No.12zx7106)the Postgraduate Innovation Fund Project of Southwest University of Science and Technology(No.14ycxjj0121)
文摘Defect evolution in a single crystal silicon which is implanted with hydrogen atoms and then annealed is investigated in the present paper by means of molecular dynamics simulation. By introducing defect density based on statistical average, this work aims to quantitatively examine defect nucleation and growth at nanoscale during annealing in Smart-Cut technology. Research focus is put on the effects of the implantation energy, hydrogen implantation dose and annealing temperature on defect density in the statistical region. It is found that most de- fects nucleate and grow at the annealing stage, and that defect density increases with the increase of the annealing temperature and the decrease of the hydrogen implantation dose. In addition, the enhancement and the impediment effects of stress field on defect density in the annealing process are discussed.
基金The authors gratefully acknowledge the financial support of this work by President Foundation of China Academy of Engineering Physics(YZJJLX2020005)National Natural Science Foundation of China(Grant No.51975492)。
文摘Tribology behaviors of energetic crystals play critical roles in the friction-induced hotspot in highenergy explosive,however,the binder and energetic crystals are not distinguished properly in previous investigations.In this study,for the first time,the nanoscale friction ofβ-octahydro-1,3,5,7-tetranitro1,3,5,7-tetrazocine(β-HMX)crystal is studied with nanoscratch tests under the ramping load mode.The results show that the nanoscale friction and wear ofβ-HMX crystal,as a typical energetic material,is highly depended on the applied load.The friction coefficient ofβ-HMX crystal is initially high when no discernible wear is observed,and then it decreases to a stable value which varies from~0.2 to~0.7,depending on the applied load,scratch direction,and crystal planes.Theβ-HMX(011)surfaces show weakly friction and wear anisotropy behavior;in contrast,theβ-HMX(110)surfaces show strongly friction and wear anisotropy behavior where the friction coefficient,critical load for the elastic–plastic deformation transition and plastic–cracking deformation transition,and deformation index at higher normal load are highly depended on the scratch directions.Further analyses indicate the slip system and direction ofβ-HMX surfaces play key roles in determining the nanoscale friction and wear ofβ-HMX surfaces.The obtained results can provide deeper insight into the friction and wear of energetic crystal materials.
基金funded by the National Key Research and Development Program of China (2018YFA0703400)the Young Scientists Fund of the National Natural Science Foundation of China (52205447)+2 种基金Changjiang Scholars Program of Chinese Ministry of Educationthe Xinghai Science Funds for Distinguished Young Scholars at Dalian University of Technologythe Collaborative Innovation Center of Major Machine Manufacturing in Liaoning。
文摘High-performance devices usually have curved surfaces, requiring high accuracy of shape and low surface roughness. It is a challenge to achieve high accuracies for form and position on a device with low surface roughness. However, due to the unique nonlinear rheology, magnetorheological fluids with hard abrasives are widely applied in ultra-precision surface finishing. Compared with conventional mechanical finishing, magnetorheological finishing displays obviously advantages, such as high precision shape of machined surface, low surface roughness and subsurface damage, and easy control for finishing processes. However, finishing performance depends on various factors, e.g. volume fraction and distribution of magnetic particles, types of hard abrasives and additives, strength of magnetic field, finishing forms. Therefore, a comprehensive review on related works is essential to understand the state-of-the-art of magnetorheological finishing and beneficial to inspire researchers to develop lower cost, higher machining accuracy and efficient approaches and setups, which demonstrates a significant guidance for development of high-performance parts in fields of aerospace, navigation and clinical medicine etc. This review starts from the rheological property of magnetorheological fluids, summarizing dynamically nonlinear rheological properties and stable finishing approaches. Then, the effect of components in magnetorheological fluids is discussed on finishing performance, consisting of magnetic particles, carrier fluid, additives and abrasives. Reasonable configuration of magnetorheological fluids, and different magnetorheological finishing methods are presented for variously curved surfaces. In addition, the current finishing forms and future directions are also addressed in this review.
基金The authors are grateful for financial support from the National Natural Science Foundation of China(Nos.51975492 and 51575462)the Scientific Research Fund of Sichuan Provincial Education Department,China(18ZA0504)+3 种基金the Research Fund Supported by Sichuan Science and Technology Program(2018JY0245)the Research Foundation of Southwest University of Science and Technology(18zx7162)the Tribology Science Fund of State Key Laboratory of Tribology(SKLTKF19B15)the Project National United Engineering Laboratory for Advanced Bearing Tribology,Henan University of Science and Technology(201910).
文摘Processing(grinding,polishing)of phosphate laser(PL)glass involves material removal at two vastly different(spatial)scales.In this study,the nano‐and macro‐tribological properties of PL glass are investigated by rubbing the glass against a SiO_(2) counter‐surface in both dry and humid conditions.The results indicate that the friction of the PL glass/SiO_(2) pair has opposing trends at the nano‐and macroscales.At the nanoscale,the friction coefficient(COF)in humid air is much higher than in dry air,which is attributed to the capillary effect of the absorbed water‐film at the interface.At the macroscale,on the other hand,the COF in humid air is lower than in dry air,because the water‐related mechanochemical wear makes the worn surface less susceptible to cracking.Material removal for PL glass is better facilitated by humid air than by dry air at both scales,because the stress‐enhanced hydrolysis accelerates the material‐removal process in glass.Moreover,the material‐removal is more sensitive to contact pressure at the macroscale,because stronger mechanical‐interaction occurs during material removal at the macroscale with the multi asperity contact mode.At the macroscale,the material removal is more sensitive to contact pressure in humid air compared to dry air.Because almost all mechanical energy is used to remove material in humid air,and most of the mechanical energy is used to produce cracks in PL glass in dry air.The results of this study can help optimize the multi‐scale surface processing of optical glasses.
基金financially supported by the National Natural Science Foundation of China(No.51975492)the Research Fund Supported by Sichuan Science and Technology Program(No.2018JY0245)+1 种基金the Natural Science Foundation of Southwest University of Science and Technology(No.19xz7163)supported by the National Science Foundation of the United States(No.NSF CMMI-1901959)。
文摘A high-throughput approach based on magnetron co-sputtering of alloy libraries is employed to investigate mechanical properties of crystalline and amorphous alloys in a ternary palladium(Pd)-tungsten(W)-silicon(Si)system with the aim to reveal the difference in plastic deformation response and extract the relevant structure-property relationships of the alloys in the system.It was found that in contrast to crystalline alloys,the amorphous ones,i.e.,metallic glasses,exhibited a much smaller fluctuation range in the plasticity parameters(Er2/H and Wp/Wt),indicating a significant difference in the plastic deformation mechanism controlling the mechanical properties for the respective alloys.We propose that the inhomogeneous deformation of amorphous alloys localized in thin shear bands is responsible for the weaker compositional dependence of both plasticity parameters,while dislocation gliding in crystalline materials is significantly more dependent on the exact structure,thus resulting in a larger scattering range.Based on the representative efficient cluster packing model,a set of composition-dependent atomic structural models is proposed to figure out the structure-property relationships of amorphous alloys in Pd-W-Si alloy system.
基金supported by the National Natural Science Foundation of China (grant no.51505133)by Key Research Project in Colleges and Universities of Henan Province (23A460010)by Opening Project of Henan Engineering Laboratory of Photoelectric Sensor and Intelligent Measurement and Control,Henan Polytechnic University (grant no.HELPSIMC-2020-006).
文摘Micro-robots have the characteristics of small size,light weight and flexible movement.To design a micro three-legged crawling robot with multiple motion directions,a novel driving scheme based on the inverse piezoelectric effect of piezoelectric ceramics was proposed.The three legs of the robot were equipped with piezoelectric bimorphs as drivers,respectively.The motion principles were analyzed and the overall force analysis was carried out with the theoretical mechanics method.The natural frequency,mode shape and amplitude were analyzed with simulation software COMSOL Multiphysics,the optimal size was determined through parametric analysis,and then the micro three-legged crawling robot was manufactured.The effects of different driving voltages,different driving frequencies,different motion bases and different loads on the motion speed of the robot were tested.It is shown that the maximum speed of single-leg driving was 35.41 cm/s,the switching ability between different motion directions was measured,and the movements in six different directions were achieved.It is demonstrated the feasibility of multi-directional motion of the structure.The research may provide a reference for the design and development of miniature piezoelectric three-legged crawling robots.
