Studying and understanding of the surface topography variation are the basis for analyzing tribological problems,and characterization of worn surface is necessary.Fractal geometry offers a more accurate description fo...Studying and understanding of the surface topography variation are the basis for analyzing tribological problems,and characterization of worn surface is necessary.Fractal geometry offers a more accurate description for surface roughness that topographic surfaces are statistically self-similar and can be quantitatively evaluated by fractal parameters.The change regularity of worn surface topography is one of the most important aspects of running-in study.However,the existing research normally adopts only one friction matching pair to explore the surface topography change,which interrupts the running-in wear process and makes the experimental result lack authenticity and objectivity.In this paper,to investigate the change regularity of surface topography during the real running-in process,a series of running-in tests by changing friction pairs under the same operating conditions are conducted on UMT-II Universal Multifunction Tester.The surface profile data are acquired by MiaoXAM2.5X-50X Ultrahigh Precision Surface 3D Profiler and analyzed using fractal dimension D,scale coefficient C and characteristic roughness Ra ＊based on root mean square（RMS） method.The characterization effects of the three parameters are discussed and compared.The results obtained show that there exists remarkable fractal feature of surface topography during running-in process,both D and Ra ＊increase gradually,while C decreases slowly as the wear-in process goes on,and all parameters tend to be stable when the wear process steps into the normal wear process.Ra ＊illustrates higher sensitivity for rough surface characterization compared with the other two parameters.In addition,the running-in test carried with a set of identical surface properties is more scientific and reasonable than the traditional one.The proposed research further indicates that the fractal method can quantitatively measure the rough surface,which also provides an evidence for running-in process identification and tribology design.展开更多
Along with the growth and expansion of cities during the time, several parts of them have depreciated and they require repairing and inspection. Damaged places and repairing them are a problem that is significant and ...Along with the growth and expansion of cities during the time, several parts of them have depreciated and they require repairing and inspection. Damaged places and repairing them are a problem that is significant and liable of each period has been looking for excogitation and resolving problems according to the existing circumstances. However, expressed concern that it is still a problem, is worn texture, which is extending fast in all cities of the world, particularly in developing countries, and this problem has gripped cities and authorities. In spite of all weaknesses and deficiency, since the majority of worn-out tissues have significant cultural, social and economic values which give identity to the cities, so paying attention to these areas and how to intervene in them is very important. The purpose of this paper is to study and consider ways of rehabilitation and renovation of the old texture of Ab-Anbar-No district in Sari, which it has been done using analytical-descriptive method. In this study, the needed information has been collected by observation, providing necessary map, library research and rehabilitation and reconstruction strategies have gained by SWOT model for analysis and internal factors (strengths and weaknesses) and external factors (threats and opportunities) of this tissue have been considered comprehensively. The results of this study show that strategies for rehabilitation and renovation of Ab-Anbar-No district are one part of the guidance, control and planning system of urban rehabilitation and modernization, as a guide for decision-making. The considered limitation of weakness and strengths in physical, environmental and functional fields have a high vulnerability and also have optimization opportunities in the economic, social and legal-administrative fields in order to take advantages for reaching perfection.展开更多
Cu-based powder metallurgy brake materials are used for aircraft widely and successfully.The characteristics of worn surface of Cu-based powder metallurgy brake materials for aircraft after working under service condi...Cu-based powder metallurgy brake materials are used for aircraft widely and successfully.The characteristics of worn surface of Cu-based powder metallurgy brake materials for aircraft after working under service condition were studied,and two main wear mechanisms were discussed.The results show that the main components of worn surface are graphite,SiO2,Fe,Cu and oxide of Fe(Fe3O4 and FeO);the worn surface can be divided into three zones:severe wear zone,mild wear zone,and low wear zone; fatigue wear and grain wear are the main wear mechanisms of Cu-based materials.Some debris kept between brake discs reduce the wear rate to a certain extent by taking part in the regeneration of friction film.展开更多
The tribological characteristics of hypereutectic Al 17Si x La alloys against heat treated GCr15 bearing steel under unlubricated conditions were investigated using a block on ring type wear testing apparatus in air a...The tribological characteristics of hypereutectic Al 17Si x La alloys against heat treated GCr15 bearing steel under unlubricated conditions were investigated using a block on ring type wear testing apparatus in air at room temperature. Microstructures and chemical compositions of worn surface and wear debris were characterized by means of SEM with EDS and XRD patterns. XRD results show that wear behaviors of Al 17Si x La alloys are similar and the typical worn surface is characterized by smooth region and crater region. The mechanically mixed layer (MML) and the wear debris are very similar in microstructures and chemical compositions, both containing the fine equiaxed aggregates and large plates and blocks from the both sliding counterparts ( α (Al) and α Fe) and some reaction products (ternary oxides, i.e. Al Fe O and Fe Si O).展开更多
Flanks of end mills are prone to wear in a long machining process.Regrinding is widely used in workshops to restore the flank to an original-like state.However,the traditional method involves material waste by trial a...Flanks of end mills are prone to wear in a long machining process.Regrinding is widely used in workshops to restore the flank to an original-like state.However,the traditional method involves material waste by trial and error and dramatically decreases the potential regrinding.Moreover,over-cut would happen to the flutes of worn cutters in the regrinding processes because of improper wheel path.This study presented a new approach to planning the wheel path for regrinding worn end mills to minimize material loss and recover the over-cut.In planning,a scaling method was developed to determine the maximum size of the new cutter according to the similarity of cutter shapes before and after regrinding.Then,the wheel path is first generated by envelope theory to regrind the worn area with a four-axis computer numerical control grinder according to the new size of cutters.Moreover,a second regrinding strategy is applied to recover the flute shape over-cut in the first grinding.Finally,the proposed method is verified by an experiment.Results showed that the proposed approach could save 25%of cutter material compared with the traditional method and ensure at least three regrinding times.This work effectively provides a general regrinding solution for the worn flank with maximum material-saving and regrinding period.展开更多
As a kind of natural nanometer materials,the attapulgite has been widely used in industry,agriculture,environment,food substance,medicament and many other fields.Few researches about attapulgite used in lubricant oil ...As a kind of natural nanometer materials,the attapulgite has been widely used in industry,agriculture,environment,food substance,medicament and many other fields.Few researches about attapulgite used in lubricant oil as additive were made,and those were only at a preliminary stage of exploration.The tribological characteristics of attapulgite powders with the different contents added to CD 15W/40 lubricant oil were researched through"plane-on-plane"configuration friction and wear tester,and the self-repairing performance of 45#steel worn surface was examined via ring-on-block configuration test.XRD,SEM,EDS,TEM were employed to analyze the surface morphologies and elementary composition of the samples'worn surface.Furthermore,wear self-repairing mechanism of attapulgite additive to lubricant oil was explored.The results showed that:the optimal content of attapulgite powders in oil CD 15W/40 was 0.5 wt%,and the stable friction coefficient can be reduced to 0.02,then the friction reduction performance can be enhanced by 82.5%;Smooth worn surface were formed of the chemical reaction film containing elements O,Si,Fe;Friction reduction and self-repairing mechanism had a relation with the crystal structure of attapulgite.展开更多
基金supported by National Natural Science Foundation of China (Grant No.50975276,Grant No.50475164)National Basic Research Program of China (973 Program,Grant No.2007CB607605)Doctoral Programs Foundation of Ministry of Education of China (Grant No.200802900513)
文摘Studying and understanding of the surface topography variation are the basis for analyzing tribological problems,and characterization of worn surface is necessary.Fractal geometry offers a more accurate description for surface roughness that topographic surfaces are statistically self-similar and can be quantitatively evaluated by fractal parameters.The change regularity of worn surface topography is one of the most important aspects of running-in study.However,the existing research normally adopts only one friction matching pair to explore the surface topography change,which interrupts the running-in wear process and makes the experimental result lack authenticity and objectivity.In this paper,to investigate the change regularity of surface topography during the real running-in process,a series of running-in tests by changing friction pairs under the same operating conditions are conducted on UMT-II Universal Multifunction Tester.The surface profile data are acquired by MiaoXAM2.5X-50X Ultrahigh Precision Surface 3D Profiler and analyzed using fractal dimension D,scale coefficient C and characteristic roughness Ra ＊based on root mean square（RMS） method.The characterization effects of the three parameters are discussed and compared.The results obtained show that there exists remarkable fractal feature of surface topography during running-in process,both D and Ra ＊increase gradually,while C decreases slowly as the wear-in process goes on,and all parameters tend to be stable when the wear process steps into the normal wear process.Ra ＊illustrates higher sensitivity for rough surface characterization compared with the other two parameters.In addition,the running-in test carried with a set of identical surface properties is more scientific and reasonable than the traditional one.The proposed research further indicates that the fractal method can quantitatively measure the rough surface,which also provides an evidence for running-in process identification and tribology design.
文摘Along with the growth and expansion of cities during the time, several parts of them have depreciated and they require repairing and inspection. Damaged places and repairing them are a problem that is significant and liable of each period has been looking for excogitation and resolving problems according to the existing circumstances. However, expressed concern that it is still a problem, is worn texture, which is extending fast in all cities of the world, particularly in developing countries, and this problem has gripped cities and authorities. In spite of all weaknesses and deficiency, since the majority of worn-out tissues have significant cultural, social and economic values which give identity to the cities, so paying attention to these areas and how to intervene in them is very important. The purpose of this paper is to study and consider ways of rehabilitation and renovation of the old texture of Ab-Anbar-No district in Sari, which it has been done using analytical-descriptive method. In this study, the needed information has been collected by observation, providing necessary map, library research and rehabilitation and reconstruction strategies have gained by SWOT model for analysis and internal factors (strengths and weaknesses) and external factors (threats and opportunities) of this tissue have been considered comprehensively. The results of this study show that strategies for rehabilitation and renovation of Ab-Anbar-No district are one part of the guidance, control and planning system of urban rehabilitation and modernization, as a guide for decision-making. The considered limitation of weakness and strengths in physical, environmental and functional fields have a high vulnerability and also have optimization opportunities in the economic, social and legal-administrative fields in order to take advantages for reaching perfection.
基金Project(2003AA305680)supported by the Hi-Tech Research and Development Program of China
文摘Cu-based powder metallurgy brake materials are used for aircraft widely and successfully.The characteristics of worn surface of Cu-based powder metallurgy brake materials for aircraft after working under service condition were studied,and two main wear mechanisms were discussed.The results show that the main components of worn surface are graphite,SiO2,Fe,Cu and oxide of Fe(Fe3O4 and FeO);the worn surface can be divided into three zones:severe wear zone,mild wear zone,and low wear zone; fatigue wear and grain wear are the main wear mechanisms of Cu-based materials.Some debris kept between brake discs reduce the wear rate to a certain extent by taking part in the regeneration of friction film.
文摘The tribological characteristics of hypereutectic Al 17Si x La alloys against heat treated GCr15 bearing steel under unlubricated conditions were investigated using a block on ring type wear testing apparatus in air at room temperature. Microstructures and chemical compositions of worn surface and wear debris were characterized by means of SEM with EDS and XRD patterns. XRD results show that wear behaviors of Al 17Si x La alloys are similar and the typical worn surface is characterized by smooth region and crater region. The mechanically mixed layer (MML) and the wear debris are very similar in microstructures and chemical compositions, both containing the fine equiaxed aggregates and large plates and blocks from the both sliding counterparts ( α (Al) and α Fe) and some reaction products (ternary oxides, i.e. Al Fe O and Fe Si O).
基金supported by the National Key R&D Program of China(Grant No.2020YFB1711603)the Key Technology R&D Program of Shandong Province,China(Grant No.2020CXGC010304)the National Natural Science Foundation of China(Grant No.52175473).
文摘Flanks of end mills are prone to wear in a long machining process.Regrinding is widely used in workshops to restore the flank to an original-like state.However,the traditional method involves material waste by trial and error and dramatically decreases the potential regrinding.Moreover,over-cut would happen to the flutes of worn cutters in the regrinding processes because of improper wheel path.This study presented a new approach to planning the wheel path for regrinding worn end mills to minimize material loss and recover the over-cut.In planning,a scaling method was developed to determine the maximum size of the new cutter according to the similarity of cutter shapes before and after regrinding.Then,the wheel path is first generated by envelope theory to regrind the worn area with a four-axis computer numerical control grinder according to the new size of cutters.Moreover,a second regrinding strategy is applied to recover the flute shape over-cut in the first grinding.Finally,the proposed method is verified by an experiment.Results showed that the proposed approach could save 25%of cutter material compared with the traditional method and ensure at least three regrinding times.This work effectively provides a general regrinding solution for the worn flank with maximum material-saving and regrinding period.
基金National Natural Science Foundations of China(50735006,50904072)"973"Project(2007CB607601)China Postdoctoral Science Foundation(20090461452)
文摘As a kind of natural nanometer materials,the attapulgite has been widely used in industry,agriculture,environment,food substance,medicament and many other fields.Few researches about attapulgite used in lubricant oil as additive were made,and those were only at a preliminary stage of exploration.The tribological characteristics of attapulgite powders with the different contents added to CD 15W/40 lubricant oil were researched through"plane-on-plane"configuration friction and wear tester,and the self-repairing performance of 45#steel worn surface was examined via ring-on-block configuration test.XRD,SEM,EDS,TEM were employed to analyze the surface morphologies and elementary composition of the samples'worn surface.Furthermore,wear self-repairing mechanism of attapulgite additive to lubricant oil was explored.The results showed that:the optimal content of attapulgite powders in oil CD 15W/40 was 0.5 wt%,and the stable friction coefficient can be reduced to 0.02,then the friction reduction performance can be enhanced by 82.5%;Smooth worn surface were formed of the chemical reaction film containing elements O,Si,Fe;Friction reduction and self-repairing mechanism had a relation with the crystal structure of attapulgite.
