Paper-based friction materials are porous materials that exhibit anisotropy;they exhibit random pore sizes and quantities during their preparation,thereby rendering the control of their pore structure difficult.Compos...Paper-based friction materials are porous materials that exhibit anisotropy;they exhibit random pore sizes and quantities during their preparation,thereby rendering the control of their pore structure difficult.Composites with different pore structures are obtained by introducing chemical foaming technology during their preparation to regulate their pore structure and investigate the effect of pore structure on the properties of paper-based friction materials.The results indicate that the skeleton density,total pore area,average pore diameter,and porosity of the materials increase after chemical foaming treatment,showing a more open pore structure.The addition of an organic chemical foaming agent improves the curing degree of the matrix significantly.Consequently,the thermal stability of the materials improves significantly,and the hardness and elastic modulus of the matrix increase by 73.7%and 49.4%,respectively.The dynamic friction coefficient increases and the wear rate is reduced considerably after optimizing the pore structure.The wear rate,in particular,decreases by 47.7%from 2.83×10^(−8) to 1.48×10^(−8)cm^(3)/J as the foaming agent content increases.Most importantly,this study provides an effective method to regulate the pore structure of wet friction materials,which is conducive to achieving the desired tribological properties.展开更多
In this study,the effect of hot calendering process on the microstructure and properties of poly(p-phenylene terephthalamide)(PPTA) paper-based materials was investigated.The microstructures of the fracture surface,cr...In this study,the effect of hot calendering process on the microstructure and properties of poly(p-phenylene terephthalamide)(PPTA) paper-based materials was investigated.The microstructures of the fracture surface,crystalline structure,and single fiber strength of the PPTA paperbased materials as well as the different bonding behaviors between the PPTA fibers and PPTA fibrids obtained before and after the hot calendering process were examined.The results indicated that a high linear pressure would result in a limited improvement of the strength owing to the unimproved paper structure.The optimal values of tensile index and dielectric strength of 56.6 N·m/g and 27.6 kV/mm,respectively,could only be achieved with a synergistic effects of hot calendering temperature and linear pressure(240℃ and 110 k N/m,respectively).This result suggested it was possible to achieve a significant reinforcement and improvement in the interfacial bonding of functional PPTA paper-based materials,and avoid the formation of unexpected pleats and cracks in PPTA paper-based materials during the hot calendering process.展开更多
Three reaction systems of MoS_2-Fe, FeS -Fe, and Fe S-Fe-Mo were designed to investigate the use of FeS as an alternative to MoS_2 for producing Fe-based friction materials. Samples were prepared by powder metallurgy,...Three reaction systems of MoS_2-Fe, FeS -Fe, and Fe S-Fe-Mo were designed to investigate the use of FeS as an alternative to MoS_2 for producing Fe-based friction materials. Samples were prepared by powder metallurgy, and their phase compositions, microstructures, mechanical properties, and friction performance were characterized. The results showed that MoS_2 reacts with the matrix to produce iron-sulfides and Mo when sintered at 1050°C. Iron-sulfides produced in the MoS_2-Fe system were distributed uniformly and continuously in the matrix, leading to optimal mechanical properties and the lowest coefficient of friction among the systems studied. The lubricity observed was hypothesized to originate from the iron-sulfides produced. The Fe S-Fe-Mo system showed a phase composition, porosity, and density similar to those of the MoS_2-Fe system, but an uneven distribution of iron-sulfides and Mo in this system resulted in less-optimal mechanical properties. Finally, the Fe S-Fe system showed the poorest mechanical properties among the systems studied because of the lack of Mo reinforcement. In friction tests, the formation of a sulfide layer contributed to a decrease in coefficient of friction（COF） in all of the samples.展开更多
Molybdenum disulfide(MoS_2) is one of the most commonly used solid lubricants for Cu–Fe-based friction materials. Nevertheless, MoS_2 reacts with metal matrices to produce metal sulfides(e.g., FeS) and Mo during sint...Molybdenum disulfide(MoS_2) is one of the most commonly used solid lubricants for Cu–Fe-based friction materials. Nevertheless, MoS_2 reacts with metal matrices to produce metal sulfides(e.g., FeS) and Mo during sintering, and the lubricity of the composite may be related to the generation of FeS. Herein, the use of FeS as an alternative to MoS_2 for producing Cu–Fe-based friction materials was investigated. According to the reaction principle of thermodynamics, two composites—one with MoS_2(Fe–Cu–MoS_2 sample) and the other with FeS(FeS–Cu_2S–Cu–Fe–Mo sample), were prepared and their friction behaviors and mechanical properties were compared. The results showed that MoS_2 reacted with the Cu–Fe matrix to produce FeS, metallic ternary sulfides, and Mo when sintered at 1050°C. The MoS_2–Cu–Fe and FeS–Cu_2S–Cu–Fe–Mo samples thereby exhibited similar characteristics with respect to phase composition, density, hardness, and tribological behaviors. Micrographs of the worn surfaces revealed that the stable friction regime for both composites stemmed from the iron sulfides friction layers rather than from the molybdenum sulfides layers.展开更多
Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding （FSW） experiments. Defect-free weld was obtained when aluminum and m...Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding （FSW） experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al3Mg2 and Al12Mg17, were formed sequentially at Al6013/Mg interface.展开更多
A mathematical model is established to describe a contact problem between a deformable body and a foundation. The contact is bilateral and modelled with a nonlocal friction law, in which adhesion is taken into account...A mathematical model is established to describe a contact problem between a deformable body and a foundation. The contact is bilateral and modelled with a nonlocal friction law, in which adhesion is taken into account. Evolution of the bonding field is described by a first-order differential equation. The materials behavior is modelled with a nonlinear viscoelastic constitutive law. A variational formulation of the mechanical problem is derived, and the existence and uniqueness of the weak solution can be proven if the coefficient of friction is sufficiently small. The proof is based on arguments of time-dependent variational inequalities, differential equations, and the Banach fixed-point theorem.展开更多
Key methods developed and used in the USSR and in the Russian Federation to determine the impact and friction sensitivity of energetic materials and explosives have been discussed.Experimental methodologies and instru...Key methods developed and used in the USSR and in the Russian Federation to determine the impact and friction sensitivity of energetic materials and explosives have been discussed.Experimental methodologies and instruments that underlie the assessment of their production and handling safety have been described.Studies of a large number of compounds have revealed relationships between their sensitivity parameters and structure of individual compounds and compositions.The range of change of physical and chemical characteristics for the compounds we examined covers the entire region of their existence.Theoretical methodology and equations have been formulated to estimate the impact and friction sensitivity parameters of energetic materials and to evaluate the technological safety in use.The developed methodology is characterized by high-accuracy calculations and prediction of sensitivity parameters.展开更多
Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were ...Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy （SEM）, and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820℃. Density of the final samples decreased with increasing the amount of reinforcing elements （ZrSiO4） before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements （ZrSiO4）. With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0. 5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4 showed abrasive wear behaviour, increasing the amount of ZrSiO4 resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4 showed the best results.展开更多
A fixed-point observation method was designed to research the dynamic tribological performance of one certain resin-based friction materials. The friction test was performed through a constant speed friction tester un...A fixed-point observation method was designed to research the dynamic tribological performance of one certain resin-based friction materials. The friction test was performed through a constant speed friction tester under various temperature conditions. It was found that the dynamic tribological performance of materials has a good consistency with the dynamic evolution of worn surfaces. At lower temperatures, the friction coefficient and wear rate were constant, resulted from the stable worn surfaces. At higher temperatures, the friction coefficient increased gradually, while the wear rate decreased, due to the increasing contact area and Fe concentration. A fade occurred above 250 ℃, which can be explained by the degradation of binders.展开更多
Brake friction materials with different zinc powder contents(0,2,4,6,8 wt.%)were fabricated via powder metallurgy method.The results indicate that with the increasing zinc powder content,the density and thermal conduc...Brake friction materials with different zinc powder contents(0,2,4,6,8 wt.%)were fabricated via powder metallurgy method.The results indicate that with the increasing zinc powder content,the density and thermal conductivity of the materials gradually increase,while the hardness decreases monotonously.With increasing zinc powder content,the curve of the nominal friction coefficient shows fluctuating trend but the lowest friction coefficient also shows an increase.However,the wear rate and braking noise of the friction material monotonously decrease with increasing zinc content.This effect may be attributed to the transformation of the tribological mechanism from adhesive wear and abrasive wear to adhesive wear.The brake friction material with 4 wt.%zinc powder exhibits both the best tribological and noise performance.展开更多
The 3D needled C/SiC brake materials modified with graphite were prepared by a combined process of the chemical vapor infiltration,slurry infiltration and liquid silicon infiltration process.The microstructure and fri...The 3D needled C/SiC brake materials modified with graphite were prepared by a combined process of the chemical vapor infiltration,slurry infiltration and liquid silicon infiltration process.The microstructure and frictional properties of the brake materials were investigated.The density and open porosity of the materials as-received were about(2.1±0.1)g/cm3and(5±1)%,respectively.The brake materials were composed of 59%C,39%SiC,and 2%Si(mass fraction).The content of Si in the C/SiC brake materials modified with graphite was far less than that in the C/SiC brake materials without being modified with graphite,and the Si was dispersed.The braking curve of the 3D needled C/SiC modified with graphite was smooth,which can ensure the smooth and comfortable braking.The frictional properties under wet condition of the 3D needled C/SiC modified with graphite showed no fading.And the linear wear rate of the C/SiC modified with graphite was lower than that of the C/SiC unmodified.展开更多
Mg alloys,as a new generation of biodegradable bone implant materials,are facing two tremendous challenges of enhancing strength and reducing degradation rate in physiological environment to meet clinical needs.In thi...Mg alloys,as a new generation of biodegradable bone implant materials,are facing two tremendous challenges of enhancing strength and reducing degradation rate in physiological environment to meet clinical needs.In this study,tricalcium phosphate(β-TCP)particles were dispersed in Mg–2 Zn–0.46 Y–0.5 Nd alloy by friction stir processing(FSP)to produce Mg-based functional gradient materials(Mg/β-TCP FGM).On the surface of Mg/β-TCP FGM,the hydroxyapatite(HA)coating was prepared by electrodeposition.The effects of FSP and electrochemical parameter on the microstructure,microhardness,bonding strength and corrosion performance of the Mg/β-TCP FGM were investigated.After four passes of FSP,a uniform and fine-grained structure was formed in Mg/β-TCP and the microhardness increased from 47.9 to 76.3 HV.Compared to the samples withoutβ-TCP,the bonding strength of the Mg/β-TCP FGM increased from 23.1±0.462 to 26.3±0.526 MPa and the addition of degradableβ-TCP contributed to the in situ growth of HA coating.The thickness of HA coating could be dominated by controlling the parameters of electrodeposition.According to the results of immersion tests and electrochemical tests in simulated body fluid,it indicated that the degradation rate of the Mg/β-TCP FGM could be adjusted.展开更多
Discarded train brake shoes mainly consist of steel-backed friction material. To be better reutilized, its essential features and its interaction in cement-based material need to be studied. Consequently, particle siz...Discarded train brake shoes mainly consist of steel-backed friction material. To be better reutilized, its essential features and its interaction in cement-based material need to be studied. Consequently, particle size analysis, SEM, IR and TGA were used to investigate two types of waste brake shoes, i e, mechanical grinding friction reclaimed material of waste brake-shoe（G-FRMWBS） and pyrolysis-friction reclaimed materials of waste brake-shoe（P-FRMWBS）. The latter exhibited less organic content, larger range of particle size distribution and smaller medium particle diameter. Both types contained inorganic particles of spherical and irregular shapes, striped with steel fiber. Upon isometric substituting fine aggregates, G-FRMWBS lifted the strength of mortar effectively that was increased by 16.6% and 17.5% when the replacing rate was 5%; the value went up to 19.2% and 19.2% when the replacing rate was 10%. Moreover, inclusion of FRMWBS enhanced the chloride penetration resistance, and optimized the pore characteristic and ITZ（interfacial transition zone） as well.展开更多
The perturbation method is applied to investigate the frictionally excited thermoelastic dynamic instability (TEDI) of a functionally graded material (FGM) coating in half-plane sliding against a homogeneous half-plan...The perturbation method is applied to investigate the frictionally excited thermoelastic dynamic instability (TEDI) of a functionally graded material (FGM) coating in half-plane sliding against a homogeneous half-plane. We assume that the thermoelastic properties of the FGM vary exponentially with thickness. We also examine the effects of the gradient index, sliding speed, and friction coefficient on the TEDI for various material combinations. The transverse normal stress for two different coating structures is calculated. Furthermore, the frictional sliding stability of two different coating structures is analyzed. The obtained results show that use of FGM coatings can improve the TEDI of this sliding system and reduce the possibility of interfacial failure by controlling the interfacial tensile stress.展开更多
In this study,effects of B addition on the sintering densification,microstructure,hardness,friction and wear properties of sintered Fe-2.4C-4Cr-1Mo-0.5P-0.7Si-2.5Cu(in wt%)were investigated.In spite of the decreased s...In this study,effects of B addition on the sintering densification,microstructure,hardness,friction and wear properties of sintered Fe-2.4C-4Cr-1Mo-0.5P-0.7Si-2.5Cu(in wt%)were investigated.In spite of the decreased sintered density,the addition of B changes the phase composition of the materials and their ratio.Moreover,hardness of either the matrix or the liquid solidification structure dramatically increases.These changes in micro structure result in higher friction coefficient and lower wear loss.It is observed that the addition of0.1 wt%B offers the optimum friction and wear properties with a running-in period of only 30 s and wear volume loss of 0.006 mm^(3) under the testing conditions.Such friction and wear properties are superior to those of the other two widely used cam materials,cast iron and 45 steel.展开更多
Friction stir spot welding technique was used to join dissimilar combinations of aluminium alloy(Al5052)with copperalloy(C27200)and friction stir spot welding windows such as tool rotational speed–dwell time and tool...Friction stir spot welding technique was used to join dissimilar combinations of aluminium alloy(Al5052)with copperalloy(C27200)and friction stir spot welding windows such as tool rotational speed–dwell time and tool rotational speed?plungedepth diagrams for effective joining of these materials were developed.Using a central composite design model,empirical relationswere developed to predict the changes in tensile shear failure load values and interface hardness of the joints with three processparameters such as tool rotational speed,plunge depth and dwell time.The adequacy of the developed model was verified usingANOVA analysis at95%confidence level.Response surface methodology was used to optimize the developed model to maximizetensile strength and minimize interface hardness.A high tensile shear failure load value of3850N and low interface hardness valueof HV81was observed for joints made under optimum conditions,and validation experiments confirmed the high predictability ofthe developed model with error less than2%.The operating windows developed shall act as reference maps for future designengineers in choosing appropriate friction stir spot welding process parameter values to obtain good joints.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 friction sheets working process was analyzed. It is found that its characteristic is microregion instantaneous high temperature and the current cooling method, making the sheets cooled by the lubricating oil flowi...The friction sheets working process was analyzed. It is found that its characteristic is microregion instantaneous high temperature and the current cooling method, making the sheets cooled by the lubricating oil flowing through the friction surface, is not very efficient. Then, intelligent materials concept was introduced, the component and microstructure of intelligent Cu-based friction materials were designed, and the intelligent Cu-based wet friction materials as well as sheets were manufactured. And the intelligent friction materials working principle, i.e. the materials cooling the friction microregion in real time or the friction sheets cutting the peak value of microregion instantaneous high temperature during friction process, was given depending on the characteristics of the materials’ and friction sheets’ working process. Finally, it is indicated that the intelligent friction sheets excell the currently used friction sheets in properties, including anti-heating property, anti-wearing property as well as friction characteristic.展开更多
In order to study the effects of preparation process on the performance and microstructure of the materials, semi-metal friction materials doping rare earths were produced. Different influencing factors in preparation...In order to study the effects of preparation process on the performance and microstructure of the materials, semi-metal friction materials doping rare earths were produced. Different influencing factors in preparation processes (forming pressure, hot-pressing temperature, etc.) were investigated and the optimum technological parameters were selected. The results showed that preparation processes has correlation with the properties of the materials. The morphology of worn surface was observed by scanning electronic microscope, and the conclusion was drawn that wear mechanisms of the materials were mainly abrasive wear, adhesive wear and fatigue wear. Doping RE in the materials can improve the interfacial bonding among the components of semi-metal friction materials and make the structure of the materials more impact.展开更多
Rare earth compounds as modifiers used widely in modern friction materials can enhance the interfacial binding of constituents of materials and improve the comprehensive properties of materials evidently. However, the...Rare earth compounds as modifiers used widely in modern friction materials can enhance the interfacial binding of constituents of materials and improve the comprehensive properties of materials evidently. However, there are still few reports on application of rare earth in automotive friction materials. In order to study the effect mechanism of rare earths in friction materials, a rare earth compound was selected as additive and the effects of materials doped with or without rare earth on friction and wear properties of materials were studied. The microstructure and worn surface morphology were observed by scanning electron microscopy and the macro performance was discussed. Worn surface element constitution of materials was analyzed by energy dispersive spectroscopy. Effect mechanism of rare earths on friction and wear behaviors of friction materials were discussed. The results show that doping rare earths in friction materials can stabilize friction coefficient, lower the wear rate of materials and increase the impact strength of materials. The flexibility and fracture resistance of materials is greatly improved. Worn surface of materials doped with rare earth is compact and the surface adhesion is greatly enhanced.展开更多
基金This research was supported by the National Natural Science Foundation of China(Nos.51872176 and 52172102)the Shaanxi Key Industry Innovation Chain Project(No.2021ZDLGY14-04)+1 种基金the Science Fund for Distinguished Young Scholars of Shaanxi Province(No.2019JC-32)the Fundamental Research Funds for the Central Universities(No.G2020KY05130).
文摘Paper-based friction materials are porous materials that exhibit anisotropy;they exhibit random pore sizes and quantities during their preparation,thereby rendering the control of their pore structure difficult.Composites with different pore structures are obtained by introducing chemical foaming technology during their preparation to regulate their pore structure and investigate the effect of pore structure on the properties of paper-based friction materials.The results indicate that the skeleton density,total pore area,average pore diameter,and porosity of the materials increase after chemical foaming treatment,showing a more open pore structure.The addition of an organic chemical foaming agent improves the curing degree of the matrix significantly.Consequently,the thermal stability of the materials improves significantly,and the hardness and elastic modulus of the matrix increase by 73.7%and 49.4%,respectively.The dynamic friction coefficient increases and the wear rate is reduced considerably after optimizing the pore structure.The wear rate,in particular,decreases by 47.7%from 2.83×10^(−8) to 1.48×10^(−8)cm^(3)/J as the foaming agent content increases.Most importantly,this study provides an effective method to regulate the pore structure of wet friction materials,which is conducive to achieving the desired tribological properties.
基金the financial support to this research from the open fund of state key laboratory for modification of chemical fibers and polymer materials (LK1601)projects of education department of Shaanxi provincial government (15JF012)National Natural Science Foundation of China (51402180)
文摘In this study,the effect of hot calendering process on the microstructure and properties of poly(p-phenylene terephthalamide)(PPTA) paper-based materials was investigated.The microstructures of the fracture surface,crystalline structure,and single fiber strength of the PPTA paperbased materials as well as the different bonding behaviors between the PPTA fibers and PPTA fibrids obtained before and after the hot calendering process were examined.The results indicated that a high linear pressure would result in a limited improvement of the strength owing to the unimproved paper structure.The optimal values of tensile index and dielectric strength of 56.6 N·m/g and 27.6 kV/mm,respectively,could only be achieved with a synergistic effects of hot calendering temperature and linear pressure(240℃ and 110 k N/m,respectively).This result suggested it was possible to achieve a significant reinforcement and improvement in the interfacial bonding of functional PPTA paper-based materials,and avoid the formation of unexpected pleats and cracks in PPTA paper-based materials during the hot calendering process.
基金Financial supports from the National Natural Science Foundation of China(No.51572026)the State Key Laboratory of Traction Power,Southwest Jiaotong University,China(No.TPL1612)
文摘Three reaction systems of MoS_2-Fe, FeS -Fe, and Fe S-Fe-Mo were designed to investigate the use of FeS as an alternative to MoS_2 for producing Fe-based friction materials. Samples were prepared by powder metallurgy, and their phase compositions, microstructures, mechanical properties, and friction performance were characterized. The results showed that MoS_2 reacts with the matrix to produce iron-sulfides and Mo when sintered at 1050°C. Iron-sulfides produced in the MoS_2-Fe system were distributed uniformly and continuously in the matrix, leading to optimal mechanical properties and the lowest coefficient of friction among the systems studied. The lubricity observed was hypothesized to originate from the iron-sulfides produced. The Fe S-Fe-Mo system showed a phase composition, porosity, and density similar to those of the MoS_2-Fe system, but an uneven distribution of iron-sulfides and Mo in this system resulted in less-optimal mechanical properties. Finally, the Fe S-Fe system showed the poorest mechanical properties among the systems studied because of the lack of Mo reinforcement. In friction tests, the formation of a sulfide layer contributed to a decrease in coefficient of friction（COF） in all of the samples.
基金financially supported by the National Natural Science Foundation of China (No. 51572026)
文摘Molybdenum disulfide(MoS_2) is one of the most commonly used solid lubricants for Cu–Fe-based friction materials. Nevertheless, MoS_2 reacts with metal matrices to produce metal sulfides(e.g., FeS) and Mo during sintering, and the lubricity of the composite may be related to the generation of FeS. Herein, the use of FeS as an alternative to MoS_2 for producing Cu–Fe-based friction materials was investigated. According to the reaction principle of thermodynamics, two composites—one with MoS_2(Fe–Cu–MoS_2 sample) and the other with FeS(FeS–Cu_2S–Cu–Fe–Mo sample), were prepared and their friction behaviors and mechanical properties were compared. The results showed that MoS_2 reacted with the Cu–Fe matrix to produce FeS, metallic ternary sulfides, and Mo when sintered at 1050°C. The MoS_2–Cu–Fe and FeS–Cu_2S–Cu–Fe–Mo samples thereby exhibited similar characteristics with respect to phase composition, density, hardness, and tribological behaviors. Micrographs of the worn surfaces revealed that the stable friction regime for both composites stemmed from the iron sulfides friction layers rather than from the molybdenum sulfides layers.
文摘Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding （FSW） experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al3Mg2 and Al12Mg17, were formed sequentially at Al6013/Mg interface.
文摘A mathematical model is established to describe a contact problem between a deformable body and a foundation. The contact is bilateral and modelled with a nonlocal friction law, in which adhesion is taken into account. Evolution of the bonding field is described by a first-order differential equation. The materials behavior is modelled with a nonlinear viscoelastic constitutive law. A variational formulation of the mechanical problem is derived, and the existence and uniqueness of the weak solution can be proven if the coefficient of friction is sufficiently small. The proof is based on arguments of time-dependent variational inequalities, differential equations, and the Banach fixed-point theorem.
文摘Key methods developed and used in the USSR and in the Russian Federation to determine the impact and friction sensitivity of energetic materials and explosives have been discussed.Experimental methodologies and instruments that underlie the assessment of their production and handling safety have been described.Studies of a large number of compounds have revealed relationships between their sensitivity parameters and structure of individual compounds and compositions.The range of change of physical and chemical characteristics for the compounds we examined covers the entire region of their existence.Theoretical methodology and equations have been formulated to estimate the impact and friction sensitivity parameters of energetic materials and to evaluate the technological safety in use.The developed methodology is characterized by high-accuracy calculations and prediction of sensitivity parameters.
文摘Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy （SEM）, and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820℃. Density of the final samples decreased with increasing the amount of reinforcing elements （ZrSiO4） before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements （ZrSiO4）. With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0. 5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4 showed abrasive wear behaviour, increasing the amount of ZrSiO4 resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4 showed the best results.
基金Funded by the National High-Tech R&D Program of China(863 Program)(SS2015AA042502)
文摘A fixed-point observation method was designed to research the dynamic tribological performance of one certain resin-based friction materials. The friction test was performed through a constant speed friction tester under various temperature conditions. It was found that the dynamic tribological performance of materials has a good consistency with the dynamic evolution of worn surfaces. At lower temperatures, the friction coefficient and wear rate were constant, resulted from the stable worn surfaces. At higher temperatures, the friction coefficient increased gradually, while the wear rate decreased, due to the increasing contact area and Fe concentration. A fade occurred above 250 ℃, which can be explained by the degradation of binders.
基金Project(2016YFB1100103)supported by the National Key Research and Development Program of ChinaProject(KC1703004)supported by the Science and Technology Planning Project of Changsha City,ChinaProject(2018ZZTS127)supported by the Fundamental Research Funds for the Central Universities of Central South University,China。
文摘Brake friction materials with different zinc powder contents(0,2,4,6,8 wt.%)were fabricated via powder metallurgy method.The results indicate that with the increasing zinc powder content,the density and thermal conductivity of the materials gradually increase,while the hardness decreases monotonously.With increasing zinc powder content,the curve of the nominal friction coefficient shows fluctuating trend but the lowest friction coefficient also shows an increase.However,the wear rate and braking noise of the friction material monotonously decrease with increasing zinc content.This effect may be attributed to the transformation of the tribological mechanism from adhesive wear and abrasive wear to adhesive wear.The brake friction material with 4 wt.%zinc powder exhibits both the best tribological and noise performance.
基金Project(46-QP-2009)supported by the Research Fund of State Key Laboratory of Solidification Processing(NWPU),ChinaProject supported by the Program for Changjiang Scholars and Innovative Research Team in Chinese University
文摘The 3D needled C/SiC brake materials modified with graphite were prepared by a combined process of the chemical vapor infiltration,slurry infiltration and liquid silicon infiltration process.The microstructure and frictional properties of the brake materials were investigated.The density and open porosity of the materials as-received were about(2.1±0.1)g/cm3and(5±1)%,respectively.The brake materials were composed of 59%C,39%SiC,and 2%Si(mass fraction).The content of Si in the C/SiC brake materials modified with graphite was far less than that in the C/SiC brake materials without being modified with graphite,and the Si was dispersed.The braking curve of the 3D needled C/SiC modified with graphite was smooth,which can ensure the smooth and comfortable braking.The frictional properties under wet condition of the 3D needled C/SiC modified with graphite showed no fading.And the linear wear rate of the C/SiC modified with graphite was lower than that of the C/SiC unmodified.
基金financial support of the National Natural Science Foundation of China(No.U1804251)the National Key Research and Development Program of China(Nos.2018YFC1106703 and 2017YFB0702504).
文摘Mg alloys,as a new generation of biodegradable bone implant materials,are facing two tremendous challenges of enhancing strength and reducing degradation rate in physiological environment to meet clinical needs.In this study,tricalcium phosphate(β-TCP)particles were dispersed in Mg–2 Zn–0.46 Y–0.5 Nd alloy by friction stir processing(FSP)to produce Mg-based functional gradient materials(Mg/β-TCP FGM).On the surface of Mg/β-TCP FGM,the hydroxyapatite(HA)coating was prepared by electrodeposition.The effects of FSP and electrochemical parameter on the microstructure,microhardness,bonding strength and corrosion performance of the Mg/β-TCP FGM were investigated.After four passes of FSP,a uniform and fine-grained structure was formed in Mg/β-TCP and the microhardness increased from 47.9 to 76.3 HV.Compared to the samples withoutβ-TCP,the bonding strength of the Mg/β-TCP FGM increased from 23.1±0.462 to 26.3±0.526 MPa and the addition of degradableβ-TCP contributed to the in situ growth of HA coating.The thickness of HA coating could be dominated by controlling the parameters of electrodeposition.According to the results of immersion tests and electrochemical tests in simulated body fluid,it indicated that the degradation rate of the Mg/β-TCP FGM could be adjusted.
基金Funded by National Natural Science Foundation of China(Nos.51408380,No.51478278)Science and Technology Plan of Hebei Province,China(No.14273805D)+1 种基金He Bei Education Department(No.QN2016156)the Young Top Talent Science Research Project of Colleges and Universities in He Bei Province(No.BJ2014053)
文摘Discarded train brake shoes mainly consist of steel-backed friction material. To be better reutilized, its essential features and its interaction in cement-based material need to be studied. Consequently, particle size analysis, SEM, IR and TGA were used to investigate two types of waste brake shoes, i e, mechanical grinding friction reclaimed material of waste brake-shoe（G-FRMWBS） and pyrolysis-friction reclaimed materials of waste brake-shoe（P-FRMWBS）. The latter exhibited less organic content, larger range of particle size distribution and smaller medium particle diameter. Both types contained inorganic particles of spherical and irregular shapes, striped with steel fiber. Upon isometric substituting fine aggregates, G-FRMWBS lifted the strength of mortar effectively that was increased by 16.6% and 17.5% when the replacing rate was 5%; the value went up to 19.2% and 19.2% when the replacing rate was 10%. Moreover, inclusion of FRMWBS enhanced the chloride penetration resistance, and optimized the pore characteristic and ITZ（interfacial transition zone） as well.
基金National NaturalScience Foundation of China (Grants 11502089 and 11725207).
文摘The perturbation method is applied to investigate the frictionally excited thermoelastic dynamic instability (TEDI) of a functionally graded material (FGM) coating in half-plane sliding against a homogeneous half-plane. We assume that the thermoelastic properties of the FGM vary exponentially with thickness. We also examine the effects of the gradient index, sliding speed, and friction coefficient on the TEDI for various material combinations. The transverse normal stress for two different coating structures is calculated. Furthermore, the frictional sliding stability of two different coating structures is analyzed. The obtained results show that use of FGM coatings can improve the TEDI of this sliding system and reduce the possibility of interfacial failure by controlling the interfacial tensile stress.
基金financially supported by the National High-tech R&D Program (No.2013AA031101)the Major Science and Technology Projects (No.2012ZX04009011)the Technology Project of Huairou District in Beijing (No.2017-8)。
文摘In this study,effects of B addition on the sintering densification,microstructure,hardness,friction and wear properties of sintered Fe-2.4C-4Cr-1Mo-0.5P-0.7Si-2.5Cu(in wt%)were investigated.In spite of the decreased sintered density,the addition of B changes the phase composition of the materials and their ratio.Moreover,hardness of either the matrix or the liquid solidification structure dramatically increases.These changes in micro structure result in higher friction coefficient and lower wear loss.It is observed that the addition of0.1 wt%B offers the optimum friction and wear properties with a running-in period of only 30 s and wear volume loss of 0.006 mm^(3) under the testing conditions.Such friction and wear properties are superior to those of the other two widely used cam materials,cast iron and 45 steel.
文摘Friction stir spot welding technique was used to join dissimilar combinations of aluminium alloy(Al5052)with copperalloy(C27200)and friction stir spot welding windows such as tool rotational speed–dwell time and tool rotational speed?plungedepth diagrams for effective joining of these materials were developed.Using a central composite design model,empirical relationswere developed to predict the changes in tensile shear failure load values and interface hardness of the joints with three processparameters such as tool rotational speed,plunge depth and dwell time.The adequacy of the developed model was verified usingANOVA analysis at95%confidence level.Response surface methodology was used to optimize the developed model to maximizetensile strength and minimize interface hardness.A high tensile shear failure load value of3850N and low interface hardness valueof HV81was observed for joints made under optimum conditions,and validation experiments confirmed the high predictability ofthe developed model with error less than2%.The operating windows developed shall act as reference maps for future designengineers in choosing appropriate friction stir spot welding process parameter values to obtain good joints.
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.
文摘The friction sheets working process was analyzed. It is found that its characteristic is microregion instantaneous high temperature and the current cooling method, making the sheets cooled by the lubricating oil flowing through the friction surface, is not very efficient. Then, intelligent materials concept was introduced, the component and microstructure of intelligent Cu-based friction materials were designed, and the intelligent Cu-based wet friction materials as well as sheets were manufactured. And the intelligent friction materials working principle, i.e. the materials cooling the friction microregion in real time or the friction sheets cutting the peak value of microregion instantaneous high temperature during friction process, was given depending on the characteristics of the materials’ and friction sheets’ working process. Finally, it is indicated that the intelligent friction sheets excell the currently used friction sheets in properties, including anti-heating property, anti-wearing property as well as friction characteristic.
文摘In order to study the effects of preparation process on the performance and microstructure of the materials, semi-metal friction materials doping rare earths were produced. Different influencing factors in preparation processes (forming pressure, hot-pressing temperature, etc.) were investigated and the optimum technological parameters were selected. The results showed that preparation processes has correlation with the properties of the materials. The morphology of worn surface was observed by scanning electronic microscope, and the conclusion was drawn that wear mechanisms of the materials were mainly abrasive wear, adhesive wear and fatigue wear. Doping RE in the materials can improve the interfacial bonding among the components of semi-metal friction materials and make the structure of the materials more impact.
文摘Rare earth compounds as modifiers used widely in modern friction materials can enhance the interfacial binding of constituents of materials and improve the comprehensive properties of materials evidently. However, there are still few reports on application of rare earth in automotive friction materials. In order to study the effect mechanism of rare earths in friction materials, a rare earth compound was selected as additive and the effects of materials doped with or without rare earth on friction and wear properties of materials were studied. The microstructure and worn surface morphology were observed by scanning electron microscopy and the macro performance was discussed. Worn surface element constitution of materials was analyzed by energy dispersive spectroscopy. Effect mechanism of rare earths on friction and wear behaviors of friction materials were discussed. The results show that doping rare earths in friction materials can stabilize friction coefficient, lower the wear rate of materials and increase the impact strength of materials. The flexibility and fracture resistance of materials is greatly improved. Worn surface of materials doped with rare earth is compact and the surface adhesion is greatly enhanced.
