This work describes an experimental investigation into the influence of geometric micro-groove texture patterns on the tribological performance of stainless steel.Five geometries were studied:one with untextured and f...This work describes an experimental investigation into the influence of geometric micro-groove texture patterns on the tribological performance of stainless steel.Five geometries were studied:one with untextured and four with micro-groove textured making parallel,triangular,square and hexagonal patterns.The micro-groove textures were produced using an MFT-20laser system as well as a two-step laser surface texturing(LST)process.Tribological performance was measured using a pin-on-disk tribometer.The investigation showed that the two-step LST process could fabricate high-precision micro-grooves.The experimental data indicated that the micro-groove textured surfaces achieved the lower frictional coefficients than the untextured surface and the geometric patterns had significantly affected the tribological properties of samples in both lubricated and unlubricated states.The results were analyzed from the lubricant supplying and fluid dynamic pressure effect under lubricated conditions as well as abrasive capture and remove under dry friction conditions.展开更多
Nano-long chains were grafted over the replicated micro-grooves of shark skin in a novel attempt to replicate bio-synthetic drag reduction structure with high precision through synthetic bio-replication. Pre-treated s...Nano-long chains were grafted over the replicated micro-grooves of shark skin in a novel attempt to replicate bio-synthetic drag reduction structure with high precision through synthetic bio-replication. Pre-treated shark skin was used as casting template to prepare a flexible female die of silicone rubber by soft die formation. A waterborne epoxy resin was then used to graft long-chains of drag reduction agent and prepare a synthetic drag reduction shark skin with nano-long chain drag reduction interface and lifelike micro-grooves. Replication precision analysis shows that this technology could replicate the complicated three-dimensional morphology of a biological drag reduction surface with high precision. Drag reduction experiments show that the material had an excellent synthetic drag reduction effect, with a maximal drag reduction rate of up to 24.6% over the velocities tested.展开更多
A textured surface with a micro-groove structure exerts a distinct characteristic on drag reduction behavior. The fluid dynamic models of four textured surfaces are constructed in various profile geometries. Computati...A textured surface with a micro-groove structure exerts a distinct characteristic on drag reduction behavior. The fluid dynamic models of four textured surfaces are constructed in various profile geometries. Computational fluid dynamics is used to study the friction factors and drag reduction properties with various flow speeds on the textured surfaces. The friction coefficient varieties in the interface between the fluid and the textured surface are examined according to the simulation of the four geometries with V-shaped, saw tooth, rectangular, and semi-circular sections. The drag reduction efficiencies decrease with the increase in water velocity while it is less than a certain value. Moreover, the simulation results of the velocity, shear stress, energy, and turbulence effect on the V-shaped groove surface are presented in comparison with those of the smooth surface to illustrate the drag reduction mechanism. The results indicate that the peaks of the V-shaped grooves inhibit the lateral movement of the turbulent flow and generate the secondary vortex, which plays a key role in the impeding momentum exchange, thereby decreasing turbulent bursting intensity and reducing shear stress in the near-wall flow field. The kinetic energy and turbulence analysis shows that the vortex in the near-wall flow field on the textured surface is more stable compared to that on the smooth surface.展开更多
Surface modification,as a promising approach to improve biocompatibility of biomaterials,has captured extensive close attention among many researchers.Here,micro-milling technology was used in constructing pyramid mic...Surface modification,as a promising approach to improve biocompatibility of biomaterials,has captured extensive close attention among many researchers.Here,micro-milling technology was used in constructing pyramid micro-structures on the surface of Ti-6Al-4Vimplant.Cutting parameters,including spindle speed,feed rate and depth of cut,were optimized to control the generation of burrs.In addition,low melting point alloy was selected to extend the boundary of the workpiece as supporting material to prevent the generation of top burrs.The surface topographies were characterized using scanning electron microscope and laser scanning microscope.Results showed that the dimension of burrs decreased with the decrease of depth of cut,and the size of burrs decreased with the increase of feed rate.Moreover,burrs nearly not appeared on both sides of the micro-grooves machined with low melting point alloy(LMPA)coating.Pyramid micro-structure on the workpiece surface was built successfully by combining optimized cutting parameters(S=35kr/min,Vf=60mm/min,ap=5μm)and LMPA coating.展开更多
Using high-speed oil-filled spinning method,high quality micro copper tube with straight grooves（MCTSG） with an outer diameter of 6 mm was obtained.Then,MCTSG with an outer diameter of 3-6 mm was fabricated successf...Using high-speed oil-filled spinning method,high quality micro copper tube with straight grooves（MCTSG） with an outer diameter of 6 mm was obtained.Then,MCTSG with an outer diameter of 3-6 mm was fabricated successfully by multi-pass drawing processing method.The influence of drawing parameters on the forming of micro straight grooves was investigated based on the forming mechanism.The results show that the values of groove depth and width decrease,while the wall thickness increases as the drawing diameter decreases.At the same time,the groove depth and width increase,while the wall thickness decreases as the die angle increases.The drawing force increases as the reduction increases.Excessive copper tube reduction may results in groove folding and segmental teeth.The drawing force decreases firstly and then increases with the increases in die angle.When the die angle α is 16°,the drawing force is the smallest,indicating 16° is the optimal angle.展开更多
基金Project(51305023) supported by the National Natural Science Foundation of ChinaProject(FRF-GF-17-B20) supported by the Fundamental Research Funds for the Central Universities of China
文摘This work describes an experimental investigation into the influence of geometric micro-groove texture patterns on the tribological performance of stainless steel.Five geometries were studied:one with untextured and four with micro-groove textured making parallel,triangular,square and hexagonal patterns.The micro-groove textures were produced using an MFT-20laser system as well as a two-step laser surface texturing(LST)process.Tribological performance was measured using a pin-on-disk tribometer.The investigation showed that the two-step LST process could fabricate high-precision micro-grooves.The experimental data indicated that the micro-groove textured surfaces achieved the lower frictional coefficients than the untextured surface and the geometric patterns had significantly affected the tribological properties of samples in both lubricated and unlubricated states.The results were analyzed from the lubricant supplying and fluid dynamic pressure effect under lubricated conditions as well as abrasive capture and remove under dry friction conditions.
基金supported by the National Natural Science Foundation of China (50775006)the National Defense Basic Science Research Special Foundation (D2120060002)the Key Project of National High-Tech R&D Program of China (2009AA043802)
文摘Nano-long chains were grafted over the replicated micro-grooves of shark skin in a novel attempt to replicate bio-synthetic drag reduction structure with high precision through synthetic bio-replication. Pre-treated shark skin was used as casting template to prepare a flexible female die of silicone rubber by soft die formation. A waterborne epoxy resin was then used to graft long-chains of drag reduction agent and prepare a synthetic drag reduction shark skin with nano-long chain drag reduction interface and lifelike micro-grooves. Replication precision analysis shows that this technology could replicate the complicated three-dimensional morphology of a biological drag reduction surface with high precision. Drag reduction experiments show that the material had an excellent synthetic drag reduction effect, with a maximal drag reduction rate of up to 24.6% over the velocities tested.
基金National Natural Science Foundation of China (No.52205453)Natural Science Foundation of Shanghai,China (No.22ZR1402700)Opening Foundation of Shanghai Collaborative Innovation Center of High Performance Fibers and Composites (Province-Minitry Joint),China (No.X12812101/019)。
基金This research work was jointly supported by the National Natural Science Foundation of China，the State Key Program of National Natural Science Foundation of China
文摘A textured surface with a micro-groove structure exerts a distinct characteristic on drag reduction behavior. The fluid dynamic models of four textured surfaces are constructed in various profile geometries. Computational fluid dynamics is used to study the friction factors and drag reduction properties with various flow speeds on the textured surfaces. The friction coefficient varieties in the interface between the fluid and the textured surface are examined according to the simulation of the four geometries with V-shaped, saw tooth, rectangular, and semi-circular sections. The drag reduction efficiencies decrease with the increase in water velocity while it is less than a certain value. Moreover, the simulation results of the velocity, shear stress, energy, and turbulence effect on the V-shaped groove surface are presented in comparison with those of the smooth surface to illustrate the drag reduction mechanism. The results indicate that the peaks of the V-shaped grooves inhibit the lateral movement of the turbulent flow and generate the secondary vortex, which plays a key role in the impeding momentum exchange, thereby decreasing turbulent bursting intensity and reducing shear stress in the near-wall flow field. The kinetic energy and turbulence analysis shows that the vortex in the near-wall flow field on the textured surface is more stable compared to that on the smooth surface.
基金supported by the National Natural Science Foundations of China(Nos.51175306,51425503)the Tai Shan Scholar Foundation,the Fundamental Research Funds for the Central Universities(No.2014JC020)the Opening fund of State Key Laboratory of Nonlinear Mechanics
文摘Surface modification,as a promising approach to improve biocompatibility of biomaterials,has captured extensive close attention among many researchers.Here,micro-milling technology was used in constructing pyramid micro-structures on the surface of Ti-6Al-4Vimplant.Cutting parameters,including spindle speed,feed rate and depth of cut,were optimized to control the generation of burrs.In addition,low melting point alloy was selected to extend the boundary of the workpiece as supporting material to prevent the generation of top burrs.The surface topographies were characterized using scanning electron microscope and laser scanning microscope.Results showed that the dimension of burrs decreased with the decrease of depth of cut,and the size of burrs decreased with the increase of feed rate.Moreover,burrs nearly not appeared on both sides of the micro-grooves machined with low melting point alloy(LMPA)coating.Pyramid micro-structure on the workpiece surface was built successfully by combining optimized cutting parameters(S=35kr/min,Vf=60mm/min,ap=5μm)and LMPA coating.
基金Project(U0834002)supported by the Joint Funds of NSFC-Guangdong of ChinaProject(2009ZM0121)supported by the Fundamental Research Funds for the Central Universities,ChinaProjects(LYM09024)supported by Training Program for Excellent Young Teachers with Innovation of Guangdong University,China
文摘Using high-speed oil-filled spinning method,high quality micro copper tube with straight grooves（MCTSG） with an outer diameter of 6 mm was obtained.Then,MCTSG with an outer diameter of 3-6 mm was fabricated successfully by multi-pass drawing processing method.The influence of drawing parameters on the forming of micro straight grooves was investigated based on the forming mechanism.The results show that the values of groove depth and width decrease,while the wall thickness increases as the drawing diameter decreases.At the same time,the groove depth and width increase,while the wall thickness decreases as the die angle increases.The drawing force increases as the reduction increases.Excessive copper tube reduction may results in groove folding and segmental teeth.The drawing force decreases firstly and then increases with the increases in die angle.When the die angle α is 16°,the drawing force is the smallest,indicating 16° is the optimal angle.
