An analytical model for contact area and contact stress considering the loading history in incremental sheet forming(ISF)was established.Then,by integrating with the directional characteristics of friction force and h...An analytical model for contact area and contact stress considering the loading history in incremental sheet forming(ISF)was established.Then,by integrating with the directional characteristics of friction force and horizontal force in the process,a friction test method reflecting the forming characteristics of ISF was proposed.Friction coefficients during the forming processes of parts with different wall angles were measured under various plane curves,process paths,and lubrication conditions.Furthermore,the accuracy of the analytical model,as well as the measured friction coefficients and their variation trends,was verified through comparative analysis with experimental results,simulation data,and outcomes from other existing models.The results indicate that the influence of the plane curve characteristics and process paths of parts on the friction condition is not significant.Under the lubrication conditions of L-HM46 oil,MoS_(2)grease,graphite powder,and dry friction,the friction coefficient shows a gradually increasing trend.Notably,when the wall angle is≤40°,the friction coefficient remains relatively constant;however,when the wall angle exceeds 40°,the friction coefficient increases progressively.展开更多
The basic technology and properties of the brake blocks made of modified needle-like wollastonite and fibrous sepiolite were intensively researched.The impact strengthes and fixed velocity friction of the brake blocks...The basic technology and properties of the brake blocks made of modified needle-like wollastonite and fibrous sepiolite were intensively researched.The impact strengthes and fixed velocity friction of the brake blocks prepared by different recipes were tested. The testing results show that it is feasible for needle-like wollastonite and fibrous sepiolite to take the place of asbestos as the reinforced materials of friction materials.The braking effect of the brake blocks is the best when the ratio of the needle-like wollastonite to the fibrous sepiolite was 1∶6.展开更多
Titanium has been increasingly applied to biomedical application because of its improved mechanical characteristics, corrosion resistance and biocompatibility. However their application remains limited, due to the low...Titanium has been increasingly applied to biomedical application because of its improved mechanical characteristics, corrosion resistance and biocompatibility. However their application remains limited, due to the low strength and poor wear resistance of unalloyed titanium. The purpose of this study is to evaluate the friction and wear behavior of high-strength titanium alloys: Ti-6Al-7Nb used in femoral stem (total hip prosthesis). The oscillating friction and wear tests have been carried out in ambient air with oscillating tribotester in accord with standards ISO 7148, ASTM G99-95a, ASTM G 133-95 under different conditions of normal applied load (3, 6 and 10 N) and sliding speed (1, 15 and 25 mm.s-1), and as a counter pair we used the ball of 100C 6, 10 mm of diameter. The surface morphology of the titanium alloys has been characterized by SEM, EDAX, micro hardness, roughness analysis measurements. The behavior observed for both samples suggests that the wear and friction mechanism during the test is the same for Ti alloys, and to increase resistance to wear and friction of biomedical titanium alloys used in total hip prosthesis (femoral stems) the surface coating and treatment are required.展开更多
This paper reviews 19 apparatuses having highvelocity capabilities,describes a rotary-shear low to highvelocity friction apparatus installed at Institute of Geology,China Earthquake Administration,and reports results ...This paper reviews 19 apparatuses having highvelocity capabilities,describes a rotary-shear low to highvelocity friction apparatus installed at Institute of Geology,China Earthquake Administration,and reports results from velocity-jump tests on Pingxi fault gouge to illustrate technical problems in conducting velocity-stepping tests at high velocities.The apparatus is capable of producing plate to seismic velocities（44 mm/a to 2.1 m/s for specimens of 40 mm in diameter）,using a 22 kW servomotor with a gear/belt system having three velocity ranges.A speed range can be changed by 103 or 106by using five electromagnetic clutches without stopping the motor.Two cam clutches allow fivefold velocity steps,and the motor speed can be increased from zero to 1,500 rpm in 0.1-0.2 s by changing the controlling voltage.A unique feature of the apparatus is a large specimen chamber where different specimen assemblies can be installed easily.In addition to a standard specimen assembly for friction experiments,two pressure vessels were made for pore pressures to 70 MPa;one at room temperature and the other at temperatures to 500 °C.Velocity step tests are needed to see if the framework of rate-and-state friction is applicable or not at high velocities.We report results from velocity jump tests from 1.4 mm/s to 1.4 m/s on yellowish gouge from a Pingxi fault zone,located at the northeastern part of the Longmenshan fault system that caused the 2008 Wenchuan earthquake.An instantaneous increase in friction followed by dramatic slip weakening was observed for the yellowish gouge with smooth sliding surfaces of host rock,but no instantaneous response was recognized for the same gouge with roughened sliding surfaces.Instantaneous and transient frictional properties upon velocity steps cannot be separated easily at high velocities,and technical improvements for velocity step tests are suggested.展开更多
China's railway prestressed concrete bridge has more than 600000 holes,prestressed engineering is a key force system affecting the safety and durability of the prestressed concrete bridge structure,its constructio...China's railway prestressed concrete bridge has more than 600000 holes,prestressed engineering is a key force system affecting the safety and durability of the prestressed concrete bridge structure,its construction quality is easily affected by traditional manual operation technology,resulting in low construction efficiency and control accuracy,easy to form a hidden danger of quality and safety,it is difficult to meet the needs of less humanized,standardized intelligent construction trend.Based on the research on the intelligent prestressed construction control and testing technology and equipment for railway bridges,this paper proposes the integration of intelligent prestressed tension control and tunnel friction test of railway bridges,intelligent grouting control of tunnel and intelligent testing of beam construction quality,and sets up a complete technical system and integrated equipment for intelligent prestressed construction of bridges based on the industrial Internet of Things(IoT).Overall,improve the quality and efficiency of bridge production,construction,and management.展开更多
Previous studies have demonstrated that the surge in jacking force during the Guanjingkou project is caused by the contact conditions of the debris bentonite slurry outside the pipe.Therefore,this paper further system...Previous studies have demonstrated that the surge in jacking force during the Guanjingkou project is caused by the contact conditions of the debris bentonite slurry outside the pipe.Therefore,this paper further systematically investigates the influence of different debris slurry mass ratios(SLRs)and different particle size distributions(PSDs)on the pipe-rock friction characteristics using friction tests.The test results reveal that under the same PSD,an adequate amount of slurry(with an SLR of 1:4)consistently yields the lowest friction coefficient.When the SLR is between 1:2 and 1:3,the viscosity of the slurry reaches its peak,resulting in the highest friction coefficient.Additionally,when the PSD is 1:1:5 and 1:1:15,the friction coefficient is primarily governed by the plowing effect at the contact surface.When the PSD is 5:1:1 and 15:1:1,the friction coefficient is mainly controlled by the void ratio(VR)of debris.In the case of PSDs 1:5:1 and 1:15:1,the friction coefficient is jointly controlled by the adhesion effect of high-viscosity slurry and the plowing effect at the contact surface,and it gradually shifts towards being dominated by the VR as the amount of debris increases.Regardless of the SLRs and PSDs,the continuous deposition of debris and the injection of slurry incessantly exacerbate both the plowing and adhesion effects,creating a vicious cycle.This is the reason why the high-pressure water flushing method can not only fail to resolve the issue but also accelerate the occurrence of the surge in jacking force.展开更多
基金the National Key R&D Program of China(No.2023YFB3407003)the National Natural Science Foundation of China(No.52375378).
文摘An analytical model for contact area and contact stress considering the loading history in incremental sheet forming(ISF)was established.Then,by integrating with the directional characteristics of friction force and horizontal force in the process,a friction test method reflecting the forming characteristics of ISF was proposed.Friction coefficients during the forming processes of parts with different wall angles were measured under various plane curves,process paths,and lubrication conditions.Furthermore,the accuracy of the analytical model,as well as the measured friction coefficients and their variation trends,was verified through comparative analysis with experimental results,simulation data,and outcomes from other existing models.The results indicate that the influence of the plane curve characteristics and process paths of parts on the friction condition is not significant.Under the lubrication conditions of L-HM46 oil,MoS_(2)grease,graphite powder,and dry friction,the friction coefficient shows a gradually increasing trend.Notably,when the wall angle is≤40°,the friction coefficient remains relatively constant;however,when the wall angle exceeds 40°,the friction coefficient increases progressively.
文摘The basic technology and properties of the brake blocks made of modified needle-like wollastonite and fibrous sepiolite were intensively researched.The impact strengthes and fixed velocity friction of the brake blocks prepared by different recipes were tested. The testing results show that it is feasible for needle-like wollastonite and fibrous sepiolite to take the place of asbestos as the reinforced materials of friction materials.The braking effect of the brake blocks is the best when the ratio of the needle-like wollastonite to the fibrous sepiolite was 1∶6.
文摘Titanium has been increasingly applied to biomedical application because of its improved mechanical characteristics, corrosion resistance and biocompatibility. However their application remains limited, due to the low strength and poor wear resistance of unalloyed titanium. The purpose of this study is to evaluate the friction and wear behavior of high-strength titanium alloys: Ti-6Al-7Nb used in femoral stem (total hip prosthesis). The oscillating friction and wear tests have been carried out in ambient air with oscillating tribotester in accord with standards ISO 7148, ASTM G99-95a, ASTM G 133-95 under different conditions of normal applied load (3, 6 and 10 N) and sliding speed (1, 15 and 25 mm.s-1), and as a counter pair we used the ball of 100C 6, 10 mm of diameter. The surface morphology of the titanium alloys has been characterized by SEM, EDAX, micro hardness, roughness analysis measurements. The behavior observed for both samples suggests that the wear and friction mechanism during the test is the same for Ti alloys, and to increase resistance to wear and friction of biomedical titanium alloys used in total hip prosthesis (femoral stems) the surface coating and treatment are required.
基金supported by State Key Laboratory of Earthquake Dynamics (Project No.LED2014A06 & LED2010A05)
文摘This paper reviews 19 apparatuses having highvelocity capabilities,describes a rotary-shear low to highvelocity friction apparatus installed at Institute of Geology,China Earthquake Administration,and reports results from velocity-jump tests on Pingxi fault gouge to illustrate technical problems in conducting velocity-stepping tests at high velocities.The apparatus is capable of producing plate to seismic velocities（44 mm/a to 2.1 m/s for specimens of 40 mm in diameter）,using a 22 kW servomotor with a gear/belt system having three velocity ranges.A speed range can be changed by 103 or 106by using five electromagnetic clutches without stopping the motor.Two cam clutches allow fivefold velocity steps,and the motor speed can be increased from zero to 1,500 rpm in 0.1-0.2 s by changing the controlling voltage.A unique feature of the apparatus is a large specimen chamber where different specimen assemblies can be installed easily.In addition to a standard specimen assembly for friction experiments,two pressure vessels were made for pore pressures to 70 MPa;one at room temperature and the other at temperatures to 500 °C.Velocity step tests are needed to see if the framework of rate-and-state friction is applicable or not at high velocities.We report results from velocity jump tests from 1.4 mm/s to 1.4 m/s on yellowish gouge from a Pingxi fault zone,located at the northeastern part of the Longmenshan fault system that caused the 2008 Wenchuan earthquake.An instantaneous increase in friction followed by dramatic slip weakening was observed for the yellowish gouge with smooth sliding surfaces of host rock,but no instantaneous response was recognized for the same gouge with roughened sliding surfaces.Instantaneous and transient frictional properties upon velocity steps cannot be separated easily at high velocities,and technical improvements for velocity step tests are suggested.
基金Scientific and Technological Development Project of China Railway Design Group Co.,Ltd.(No.2022A02480005)Technology Development Project of China Railway Design Group Co.,Ltd.(No.2023A0248001).
文摘China's railway prestressed concrete bridge has more than 600000 holes,prestressed engineering is a key force system affecting the safety and durability of the prestressed concrete bridge structure,its construction quality is easily affected by traditional manual operation technology,resulting in low construction efficiency and control accuracy,easy to form a hidden danger of quality and safety,it is difficult to meet the needs of less humanized,standardized intelligent construction trend.Based on the research on the intelligent prestressed construction control and testing technology and equipment for railway bridges,this paper proposes the integration of intelligent prestressed tension control and tunnel friction test of railway bridges,intelligent grouting control of tunnel and intelligent testing of beam construction quality,and sets up a complete technical system and integrated equipment for intelligent prestressed construction of bridges based on the industrial Internet of Things(IoT).Overall,improve the quality and efficiency of bridge production,construction,and management.
基金the funding support from the National Natural Science Foundations for Young Scientists of China(Grant No.52208391)Doctoral Foundation Project of Guizhou University(Grant No.2021e78).
文摘Previous studies have demonstrated that the surge in jacking force during the Guanjingkou project is caused by the contact conditions of the debris bentonite slurry outside the pipe.Therefore,this paper further systematically investigates the influence of different debris slurry mass ratios(SLRs)and different particle size distributions(PSDs)on the pipe-rock friction characteristics using friction tests.The test results reveal that under the same PSD,an adequate amount of slurry(with an SLR of 1:4)consistently yields the lowest friction coefficient.When the SLR is between 1:2 and 1:3,the viscosity of the slurry reaches its peak,resulting in the highest friction coefficient.Additionally,when the PSD is 1:1:5 and 1:1:15,the friction coefficient is primarily governed by the plowing effect at the contact surface.When the PSD is 5:1:1 and 15:1:1,the friction coefficient is mainly controlled by the void ratio(VR)of debris.In the case of PSDs 1:5:1 and 1:15:1,the friction coefficient is jointly controlled by the adhesion effect of high-viscosity slurry and the plowing effect at the contact surface,and it gradually shifts towards being dominated by the VR as the amount of debris increases.Regardless of the SLRs and PSDs,the continuous deposition of debris and the injection of slurry incessantly exacerbate both the plowing and adhesion effects,creating a vicious cycle.This is the reason why the high-pressure water flushing method can not only fail to resolve the issue but also accelerate the occurrence of the surge in jacking force.
