The zirconium(Zr)alloy fuel cladding is one of the key structural components of a nuclear reactor and the first and most important line of defense for accommodating fission products.During the operation of nuclear rea...The zirconium(Zr)alloy fuel cladding is one of the key structural components of a nuclear reactor and the first and most important line of defense for accommodating fission products.During the operation of nuclear reactors,Zr alloy fuel cladding is subjected to extreme harsh environments,such as high temperature,high pressure and high flow rate for a long period of time.The wear and corrosion resistance of Zr alloys is important for the safe operation of nuclear reactors.Surface modification can effectively improve the corrosion and wear resistance of fuel cladding.Compared with coating technology,nitriding technology does not have problems for bonding between the coating and the substrate.Current research on surface nitriding of Zr alloys mainly focuses on plasma nitriding and ion implantation techniques.Research on laser nitriding of Zr alloy surfaces and their fretting wear characteristics is scarce.In this study,the surface of Zr alloy was treated with laser nitriding at different laser energies.The microstructure of Zr alloy treated with different laser energies and its fretting wear performance were studied.The results showed that after nitriding with different laser energies,the surface of the Zr alloy showed a typical molten state after melting,vaporizing and cooling under the thermal effect of the laser,and this state was more obvious with the increase of the laser energy.At the same time,doping of N atoms and formation of the ZrN phase led to different cooling rates in the molten zone that produced large tensile stresses after cooling.This led to cracks on the surface of Zr alloys after laser nitriding at different energies,and the crack density increased with increasing laser energy.This also led to an increase in the surface roughness of the Zr alloy with increasing laser energy after laser nitriding treatment.Due to the presence of water in the industrial nitrogen,nitrides were generated on the surface of the sample along with some oxides.When the laser energy was 100 mJ,there was no ZrN generation,and N existed mainly as a diffusion layer within the Zr alloy substrate.ZrN generated when the laser energy reached 200 mJ and above,which increased with the increase of laser energy.Due to the generation of ZrN phase and the presence of some oxides,the surface Vickers hardness of Zr alloys after laser nitriding treatment at different energies increased by 37.5%compared to Zr alloys.After laser nitriding treatment,the wear mechanism of Zr alloys changed.For the untreated Zr alloys,the wear mechanism was dominated by delamination and spalling wear,accompanied by oxidative and abrasive wear.The phenomenon of delamination and peeling decreased with the increase of laser energy.Wear mechanisms changed to predominantly abrasive wear with oxidative wear and delamination spalling.The wear volume of sample nitriding with laser energy 400 mJ was reduced by 46.5%compared with that of untreated Zr alloy.展开更多
Aiming at the issue of sliding ratio,an internal gear pair is proposed which consists of an involute internal gear and a pinion with quadratic curve teeth.Particularly,the contact pattern is point contact and the pini...Aiming at the issue of sliding ratio,an internal gear pair is proposed which consists of an involute internal gear and a pinion with quadratic curve teeth.Particularly,the contact pattern is point contact and the pinion is generated based on an involute gear.The generation method and mathematical models of the gear pair are presented.The sliding ratio is calculated and the general calculation formulas of sliding ratios are developed.Also,the comparison between the involute gear and proposed gear is made.The adaptability of center distance and contact stress are also discussed.In addition,the gear pair was manufactured and inspected according to the exactitude solid model of the gear pair.In order to confirm this model to be effective,the efficiency experiment and the contrast experiment with the involute gear pair were performed.Furthermore,these two types of pinions were analyzed by scanning electron microscope and wear depths were measured by measuring center.The experiment results show that the efficiency of the internal gear pair is stable at a range about 97.1%to 98.6%and wear depth is less than 50%of the involute gear pair.The internal gear pair is expected to have excellent transmission performance.展开更多
The collision and wear caused by inevitable clearance in kinematic pair have an effect on the dynamic characteristics of the mechanism.Therefore,we established the dynamic model of a 3RSR(R is the revolute joint and S...The collision and wear caused by inevitable clearance in kinematic pair have an effect on the dynamic characteristics of the mechanism.Therefore,we established the dynamic model of a 3RSR(R is the revolute joint and S is the spherical joint)parallel mechanism with spherical joint clearance based on the modified Flores contact force model and the modified Coulomb friction model using Newton-Euler method.The standard quaternion was introduced in the constraint equation,and the four-order Runge-Kutta method was adopted to solve the 3RSR dynamic model.The simulation results were compared and analyzed with the numerical results.The geometrical parameters of the worn ball socket were solved based on the Archard wear model,and the geometrical reconstruction of the worn surface was carried out.The geometric reconstruction parameters were substituted into the dynamic model,which was to analyze the dynamic response of the 3RSR parallel mechanism with wear and spherical joint clearance.The simulation results show that the irregular wear occurs in the spherical joint with clearance under the presence of the impact and friction force.The long-term wear will increase the fluctuation of the contact force,thereby decreasing the movement stability of the mechanism.展开更多
Because of various error factors,the detecting errors in the real-time experimental data of the wear depth affect the accuracy of the detecting data.The self-made spherical plain bearing tester was studied,and its tes...Because of various error factors,the detecting errors in the real-time experimental data of the wear depth affect the accuracy of the detecting data.The self-made spherical plain bearing tester was studied,and its testing principle of the wear depth of the spherical plain bearing was introduced.Meanwhile,the error factors affecting the wear-depth detecting precision were analyzed.Then,the comprehensive error model of the wear-depth detecting system of the spherical plain bearing was built by the multi-body system theory(MBS).In addition,the thermal deformation of the wear-depth detecting system caused by varying the environmental temperature was detected.Finally,according to the above experimental parameters,the thermal errors of the related parts of the comprehensive error model were calculated by FEM.The results show that the difference between the simulation value and the experimental value is less than 0.005 mm,and the two values are close.The correctness of the comprehensive error model is verified under the thermal error experimental conditions.展开更多
In order to solve fretting instability problem of gear shaft shoulder due to torsional vibration in mechanical system, the mathematical model of fretting instability vibration of gear shaft shoulder was established by...In order to solve fretting instability problem of gear shaft shoulder due to torsional vibration in mechanical system, the mathematical model of fretting instability vibration of gear shaft shoulder was established by adopting the method of combining kinematics and tribology, and the numerical analysis was applied to the fretting instability mechanism of gear shaft shoulder by introducing the friction instability damping ratio. The numerical results show that the main factors causing the unstable and vibrating gear shaft shoulder are the large tightening torque and too large static friction coefficient. The reasonable values of the static friction coefficient, the amount of interference and tightening torque can effectively mitigate the fretting instability phenomenon of gear shaft shoulder. The experimental results verify that damping plays a significant role in eliminating the vibration of gear shaft control system.展开更多
A new roll shifting strategy with varying stroke and varying step was investigated,Two characteristic parameters including cat ear height and gap contour smoothness were introduced to assess the effect of shifting str...A new roll shifting strategy with varying stroke and varying step was investigated,Two characteristic parameters including cat ear height and gap contour smoothness were introduced to assess the effect of shifting strategy on roll wear,and the relation between characteristic parameters and shifting strategy was established.Both varying stroke and varying step can reduce cat ear height and gap contour smoothness,so the shifting strategy with varying stroke and varying step is better than the one with either varying stroke or varying step,Based on the effect of shifting control parameters on characteristic parameters of roll wear,the selection principle of these shifting control parameters was gained.A case study was conducted to validate the proposed roll shifting strategy,reducing uncontrollable quartic loading gap contour,improving strip profile and extending rolling length of a rolling campaign.展开更多
The present study reports investigations on rheological,mechanical,thermal,tribological and morphological properties of feedstock filaments prepared with polylactic acid-polyether ketone ketone-hydroxyapatite-chitosan...The present study reports investigations on rheological,mechanical,thermal,tribological and morphological properties of feedstock filaments prepared with polylactic acid-polyether ketone ketone-hydroxyapatite-chitosan(PLA-PEKK-HAp-CS)composite for 3D printing of functional prototypes.The study consists of a series of melt processing operations on melt flow index(MFI)setup as per ASTM D-1238 for melt flow certainty followed by fixation of reinforcement composition/proportion as 94%PEKK-4%HAp-2%CS(B)by mass in PLA matrix(A).The blending of reinforcement and preparation of feedstock filament for fused deposition modeling(FDM)set up has been performed on commercial twin screw extruder(TSE).The results of study suggest that feedstock filaments prepared with blend of 95%A-5%B(by mass)at 200℃processing temperature and 100 r/min rotational speed on TSE resulted into better tensile properties(35.9 MPa peak strength and 32.3 MPa break strength)with 6.24%surface porosity,42.67 nm surface roughness(R_(a))and acceptable heat capacity(2.14 J/g).However as regards to tribological behavior,the minimum wear of 316μm was observed for sample with poor tensile properties.As regards to crash application for scaffolds the maximum toughness of 1.16 MPa was observed for 85%A-15%B(by mass)at 200℃processing temperature and 150 r/min rotational speed on TSE.展开更多
Nanoparticles are increasingly being used to improve the friction and wear performance of polymers. In this study, we investigated the tribological behavior and energy dissipation characteristics of nano-Al_2O_3-reinf...Nanoparticles are increasingly being used to improve the friction and wear performance of polymers. In this study, we investigated the tribological behavior and energy dissipation characteristics of nano-Al_2O_3-reinforced polytetrafluoroethylenepolyphenylene sulfide(PTFE-PPS) composites in a sliding system. The tribological behaviors of the composites were evaluated under different normal loads(100–300 N) at a high linear velocity(2 m/s) using a block-on-ring tester. Addition of the nano-Al_2O_3 filler improved the antiwear performance of the PTFE-PPS composites, and the friction coefficient increased slightly. The lowest wear rate was obtained when the nano-Al_2O_3 content was 3%(volume fraction). Further, the results indicated a linear correlation between wear and the amount of energy dissipated, even though the wear mechanism changed with the nano-Al_2O_3 content, independent of the normal load applied.展开更多
The prediction of the wheel wear is a fundamental problem in heavy haul railway. A numerical methodology is introduced to simulate the wheel wear evolution of heavy haul freight car. The methodology includes the spati...The prediction of the wheel wear is a fundamental problem in heavy haul railway. A numerical methodology is introduced to simulate the wheel wear evolution of heavy haul freight car. The methodology includes the spatial coupling dynamics of vehicle and track, the three-dimensional rolling contact analysis of wheel-rail, the Specht's material wear model, and the strategy for reproducing the actual operation conditions of railway. The freight vehicle is treated as a full 3D rigid multi-body model. Every component is built detailedly and various contact interactions between parts are accurately simulated, taking into account the real clearances. The wheel-rail rolling contact calculation is carried out based on Hertz's theory and Kalker's FASTSIM algorithm. The track model is built based on field measurements. The material loss due to wear is evaluated according to the Specht's model in which the wear coefficient varies with the wear intensity. In order to exactly reproduce the actual operating conditions of railway,dynamic simulations are performed separately for all possible track conditions and running velocities in each iterative step.Dimensionless weight coefficients are introduced that determine the ratios of different cases and are obtained through site survey. For the wheel profile updating, an adaptive step strategy based on the wear depth is introduced, which can effectively improve the reliability and stability of numerical calculation. At last, the wear evolution laws are studied by the numerical model for different wheels of heavy haul freight vehicle running in curves. The results show that the wear of the front wheelset is more serious than that of the rear wheelset for one bogie, and the difference is more obvious for the outer wheels. The wear of the outer wheels is severer than that of the inner wheels. The wear of outer wheels mainly distributes near the flange and the root; while the wear of inner wheels mainly distributes around the nominal rolling circle. For the outer wheel of front wheelset of each bogie, the development of wear is gradually concentrated on the flange and the developing speed increases continually with the increase of traveled distance.展开更多
文摘The zirconium(Zr)alloy fuel cladding is one of the key structural components of a nuclear reactor and the first and most important line of defense for accommodating fission products.During the operation of nuclear reactors,Zr alloy fuel cladding is subjected to extreme harsh environments,such as high temperature,high pressure and high flow rate for a long period of time.The wear and corrosion resistance of Zr alloys is important for the safe operation of nuclear reactors.Surface modification can effectively improve the corrosion and wear resistance of fuel cladding.Compared with coating technology,nitriding technology does not have problems for bonding between the coating and the substrate.Current research on surface nitriding of Zr alloys mainly focuses on plasma nitriding and ion implantation techniques.Research on laser nitriding of Zr alloy surfaces and their fretting wear characteristics is scarce.In this study,the surface of Zr alloy was treated with laser nitriding at different laser energies.The microstructure of Zr alloy treated with different laser energies and its fretting wear performance were studied.The results showed that after nitriding with different laser energies,the surface of the Zr alloy showed a typical molten state after melting,vaporizing and cooling under the thermal effect of the laser,and this state was more obvious with the increase of the laser energy.At the same time,doping of N atoms and formation of the ZrN phase led to different cooling rates in the molten zone that produced large tensile stresses after cooling.This led to cracks on the surface of Zr alloys after laser nitriding at different energies,and the crack density increased with increasing laser energy.This also led to an increase in the surface roughness of the Zr alloy with increasing laser energy after laser nitriding treatment.Due to the presence of water in the industrial nitrogen,nitrides were generated on the surface of the sample along with some oxides.When the laser energy was 100 mJ,there was no ZrN generation,and N existed mainly as a diffusion layer within the Zr alloy substrate.ZrN generated when the laser energy reached 200 mJ and above,which increased with the increase of laser energy.Due to the generation of ZrN phase and the presence of some oxides,the surface Vickers hardness of Zr alloys after laser nitriding treatment at different energies increased by 37.5%compared to Zr alloys.After laser nitriding treatment,the wear mechanism of Zr alloys changed.For the untreated Zr alloys,the wear mechanism was dominated by delamination and spalling wear,accompanied by oxidative and abrasive wear.The phenomenon of delamination and peeling decreased with the increase of laser energy.Wear mechanisms changed to predominantly abrasive wear with oxidative wear and delamination spalling.The wear volume of sample nitriding with laser energy 400 mJ was reduced by 46.5%compared with that of untreated Zr alloy.
基金Project(51575062)supported by the National Natural Science Foundation of ChinaProject(SM2014D202)supported by the Fund of Shanghai Key Laboratory of Spacecraft Mechanism,China
文摘Aiming at the issue of sliding ratio,an internal gear pair is proposed which consists of an involute internal gear and a pinion with quadratic curve teeth.Particularly,the contact pattern is point contact and the pinion is generated based on an involute gear.The generation method and mathematical models of the gear pair are presented.The sliding ratio is calculated and the general calculation formulas of sliding ratios are developed.Also,the comparison between the involute gear and proposed gear is made.The adaptability of center distance and contact stress are also discussed.In addition,the gear pair was manufactured and inspected according to the exactitude solid model of the gear pair.In order to confirm this model to be effective,the efficiency experiment and the contrast experiment with the involute gear pair were performed.Furthermore,these two types of pinions were analyzed by scanning electron microscope and wear depths were measured by measuring center.The experiment results show that the efficiency of the internal gear pair is stable at a range about 97.1%to 98.6%and wear depth is less than 50%of the involute gear pair.The internal gear pair is expected to have excellent transmission performance.
基金Project(2018YFB1307900)supported by the National Key R&D Program of ChinaProject(51775473)supported by the National Natural Science Foundation of China+3 种基金Projects(E2018203140,E2019203109)supported by the Natural Science Foundation of Hebei Province,ChinaProject(ZD2019020)supported by the Key Research Project in Higher Education Institutions of Hebei Province,ChinaProject(2017KSYS009)supported by the Key Laboratory of Robotics and Intelligent Equipment of Guangdong Regular Institutions of Higher Education,ChinaProject(KCYCXPT2017006)supported by the Innovation Center of Robotics and Intelligent Equipment of Dongguan University of Technology,China。
文摘The collision and wear caused by inevitable clearance in kinematic pair have an effect on the dynamic characteristics of the mechanism.Therefore,we established the dynamic model of a 3RSR(R is the revolute joint and S is the spherical joint)parallel mechanism with spherical joint clearance based on the modified Flores contact force model and the modified Coulomb friction model using Newton-Euler method.The standard quaternion was introduced in the constraint equation,and the four-order Runge-Kutta method was adopted to solve the 3RSR dynamic model.The simulation results were compared and analyzed with the numerical results.The geometrical parameters of the worn ball socket were solved based on the Archard wear model,and the geometrical reconstruction of the worn surface was carried out.The geometric reconstruction parameters were substituted into the dynamic model,which was to analyze the dynamic response of the 3RSR parallel mechanism with wear and spherical joint clearance.The simulation results show that the irregular wear occurs in the spherical joint with clearance under the presence of the impact and friction force.The long-term wear will increase the fluctuation of the contact force,thereby decreasing the movement stability of the mechanism.
基金Project(2014E00468R)supported by Technological Innovation Fund of Aviation Industry Corporation of China
文摘Because of various error factors,the detecting errors in the real-time experimental data of the wear depth affect the accuracy of the detecting data.The self-made spherical plain bearing tester was studied,and its testing principle of the wear depth of the spherical plain bearing was introduced.Meanwhile,the error factors affecting the wear-depth detecting precision were analyzed.Then,the comprehensive error model of the wear-depth detecting system of the spherical plain bearing was built by the multi-body system theory(MBS).In addition,the thermal deformation of the wear-depth detecting system caused by varying the environmental temperature was detected.Finally,according to the above experimental parameters,the thermal errors of the related parts of the comprehensive error model were calculated by FEM.The results show that the difference between the simulation value and the experimental value is less than 0.005 mm,and the two values are close.The correctness of the comprehensive error model is verified under the thermal error experimental conditions.
基金Project(2008AA11A116)supported by the National High Technology Research and Development Program of ChinaProject(9140A2011QT4801)supported by advanced research of the Weapon Equipment Key Fund Program,ChinaProject(61075002)supported by the Independent Subject of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body of Hunan University,China
文摘In order to solve fretting instability problem of gear shaft shoulder due to torsional vibration in mechanical system, the mathematical model of fretting instability vibration of gear shaft shoulder was established by adopting the method of combining kinematics and tribology, and the numerical analysis was applied to the fretting instability mechanism of gear shaft shoulder by introducing the friction instability damping ratio. The numerical results show that the main factors causing the unstable and vibrating gear shaft shoulder are the large tightening torque and too large static friction coefficient. The reasonable values of the static friction coefficient, the amount of interference and tightening torque can effectively mitigate the fretting instability phenomenon of gear shaft shoulder. The experimental results verify that damping plays a significant role in eliminating the vibration of gear shaft control system.
基金Project(50974039) supported by the National Natural Science Foundation of China
文摘A new roll shifting strategy with varying stroke and varying step was investigated,Two characteristic parameters including cat ear height and gap contour smoothness were introduced to assess the effect of shifting strategy on roll wear,and the relation between characteristic parameters and shifting strategy was established.Both varying stroke and varying step can reduce cat ear height and gap contour smoothness,so the shifting strategy with varying stroke and varying step is better than the one with either varying stroke or varying step,Based on the effect of shifting control parameters on characteristic parameters of roll wear,the selection principle of these shifting control parameters was gained.A case study was conducted to validate the proposed roll shifting strategy,reducing uncontrollable quartic loading gap contour,improving strip profile and extending rolling length of a rolling campaign.
基金Guru Nanak at Dev Engg. College, Ludhiana (GNDEC) and SERB (File No. IMRC/AISTDF/R&D/P-10/2017) for providing financial/technical assistance to carry out the research
文摘The present study reports investigations on rheological,mechanical,thermal,tribological and morphological properties of feedstock filaments prepared with polylactic acid-polyether ketone ketone-hydroxyapatite-chitosan(PLA-PEKK-HAp-CS)composite for 3D printing of functional prototypes.The study consists of a series of melt processing operations on melt flow index(MFI)setup as per ASTM D-1238 for melt flow certainty followed by fixation of reinforcement composition/proportion as 94%PEKK-4%HAp-2%CS(B)by mass in PLA matrix(A).The blending of reinforcement and preparation of feedstock filament for fused deposition modeling(FDM)set up has been performed on commercial twin screw extruder(TSE).The results of study suggest that feedstock filaments prepared with blend of 95%A-5%B(by mass)at 200℃processing temperature and 100 r/min rotational speed on TSE resulted into better tensile properties(35.9 MPa peak strength and 32.3 MPa break strength)with 6.24%surface porosity,42.67 nm surface roughness(R_(a))and acceptable heat capacity(2.14 J/g).However as regards to tribological behavior,the minimum wear of 316μm was observed for sample with poor tensile properties.As regards to crash application for scaffolds the maximum toughness of 1.16 MPa was observed for 85%A-15%B(by mass)at 200℃processing temperature and 150 r/min rotational speed on TSE.
基金Project(51165022)supported by the National Natural Science Foundation of ChinaProject(20122117)supported by the Lanzhou Science and Technology Bureau Foundation,ChinaProject(1310RJZA036)supported by the Natural Science Foundation of Gansu Province,China
文摘Nanoparticles are increasingly being used to improve the friction and wear performance of polymers. In this study, we investigated the tribological behavior and energy dissipation characteristics of nano-Al_2O_3-reinforced polytetrafluoroethylenepolyphenylene sulfide(PTFE-PPS) composites in a sliding system. The tribological behaviors of the composites were evaluated under different normal loads(100–300 N) at a high linear velocity(2 m/s) using a block-on-ring tester. Addition of the nano-Al_2O_3 filler improved the antiwear performance of the PTFE-PPS composites, and the friction coefficient increased slightly. The lowest wear rate was obtained when the nano-Al_2O_3 content was 3%(volume fraction). Further, the results indicated a linear correlation between wear and the amount of energy dissipated, even though the wear mechanism changed with the nano-Al_2O_3 content, independent of the normal load applied.
基金Project(U1234211)supported of the National Natural Science Foundation of ChinaProject(20120009110020)supported by the Specialized Research Fund for Ph.D. Programs of Foundation of Ministry of Education of ChinaProject(SHGF-11-32)supported the Scientific and Technological Innovation Project of China Shenhua Energy Company Limited
文摘The prediction of the wheel wear is a fundamental problem in heavy haul railway. A numerical methodology is introduced to simulate the wheel wear evolution of heavy haul freight car. The methodology includes the spatial coupling dynamics of vehicle and track, the three-dimensional rolling contact analysis of wheel-rail, the Specht's material wear model, and the strategy for reproducing the actual operation conditions of railway. The freight vehicle is treated as a full 3D rigid multi-body model. Every component is built detailedly and various contact interactions between parts are accurately simulated, taking into account the real clearances. The wheel-rail rolling contact calculation is carried out based on Hertz's theory and Kalker's FASTSIM algorithm. The track model is built based on field measurements. The material loss due to wear is evaluated according to the Specht's model in which the wear coefficient varies with the wear intensity. In order to exactly reproduce the actual operating conditions of railway,dynamic simulations are performed separately for all possible track conditions and running velocities in each iterative step.Dimensionless weight coefficients are introduced that determine the ratios of different cases and are obtained through site survey. For the wheel profile updating, an adaptive step strategy based on the wear depth is introduced, which can effectively improve the reliability and stability of numerical calculation. At last, the wear evolution laws are studied by the numerical model for different wheels of heavy haul freight vehicle running in curves. The results show that the wear of the front wheelset is more serious than that of the rear wheelset for one bogie, and the difference is more obvious for the outer wheels. The wear of the outer wheels is severer than that of the inner wheels. The wear of outer wheels mainly distributes near the flange and the root; while the wear of inner wheels mainly distributes around the nominal rolling circle. For the outer wheel of front wheelset of each bogie, the development of wear is gradually concentrated on the flange and the developing speed increases continually with the increase of traveled distance.
