In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and proper...In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and properties of the alloy were investigated in detail.The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing(ECAP)and rolling had good comprehensive properties after aging at 400℃.The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa,with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS,respectively.ECAP and cryogenic rolling introduced high density dislocations,leading to the inhibition of the softening effects and refinement of the grains.After a long time aging at 400℃,the alloy exhibited ultra-high strength with obvious increasing electrical conductivity.The high strength was attributed to the synergistic effect of work hardening,grain refinement strengthening and precipitation strengthening.The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.展开更多
Angular rolling technology can overcome the size limitation of plate mill equipment and product heavy steel plate with large unit weight or improve the production efficiency of small width spreading ratio product.With...Angular rolling technology can overcome the size limitation of plate mill equipment and product heavy steel plate with large unit weight or improve the production efficiency of small width spreading ratio product.With the DEFORM software,the numerical simulation study of the angular rolling process was carried out,and the relation laws of the width,rolling force and strain of the rolled piece under different angular rolling process conditions were obtained.The simulation results show that with the rotation angle increasing,the width of the rolled piece increases.Comparing with the conventional rolling process,the rolling force changes gradually during the biting and throwing stage of the angular rolling pass.With the rotation angle increasing,both the equivalent strains in the thickness direction and in the width direction gradually increase.According to the pattern and dimension's changing formula in the double-pass angular rolling process,the prediction model of angle,reduction and width spreading is built.The opening value of side guide is set for the rotation angle controlling.For one 5000 mm heavy plate mill,the automation control system was modified,and the angular rolling technology was applied online.The absolute deviation of target width does not exceed±20 mm and the relative deviation does not exceed 1%.The large unit weight plate that cannot be rolled with traditional process,can be produced now,and the annual output increases by 10000 t.展开更多
Sliding and spinning behaviors significantly affect the performance of rolling bearings,especially for dry-lubricated bearings,micro and macro sliding may lead to increased wear of the solid lubricating film.A unified...Sliding and spinning behaviors significantly affect the performance of rolling bearings,especially for dry-lubricated bearings,micro and macro sliding may lead to increased wear of the solid lubricating film.A unified rolling contact tribology analytical model is proposed for dry-lubricated angular contact ball bearings(ACBBs)considering the extreme conditions including high combined loads and rolling contact effects.A comprehensive solution framework is proposed to ensure the robustness of the model under different loading conditions.Equilibrium equations are solved to study the effects of friction coefficients,rotating speeds,and combined loads on the skidding and spinning characteristics of the ACBB.The results show that the rolling contact effects and combined loads significantly affect the skidding and spinning performance of the ACBB.Further analysis reveals that the skidding mechanism is related to the interaction between ball kinematical motion and traction forces.The developed analytical model is proved to more accurately predict the bearing kinematical and tribological behavior as it discards the raceway control hypothesis and considers the macro/micro-slipping,creepage,and self-spinning motions of the ball,which is validated using both the existing pure axial loading dry-lubricated ACBB model and the classical Jones–Harris model.The study would provide some guidance for the structure and lubrication design of dry-lubricated ACBBs.展开更多
In this paper,we present an alternative technique for detecting changes in the operating conditions of rolling element bearings(REBs)that can lead to premature failure.The developed technique is based on measuring the...In this paper,we present an alternative technique for detecting changes in the operating conditions of rolling element bearings(REBs)that can lead to premature failure.The developed technique is based on measuring the kinematics of the bearing cage.The rotational motion of the cage is driven by traction forces generated in the contacts of the rolling elements with the races.It is known that the cage angular frequency relative to shaft angular frequency depends on the bearing load,the bearing speed,and the lubrication condition since these factors determine the lubricant film thickness and the associated traction forces.Since a large percentage of REB failures are due to misalignment or lubrication problems,any evidence of these conditions should be interpreted as an incipient fault.In this paper,a novel method for the measurement of the instantaneous angular speed(IAS)of the cage is developed.The method is evaluated in a deep groove ball bearing test rig equipped with a cage IAS sensor,as well as a custom acoustic emission(AE)transducer and a piezoelectric accelerometer.The IAS of the cage is analyzed under different bearing loads and shaft speeds,showing the dependence of the cage angular speed with the calculated lubricant film thickness.Typical bearing faulty operating conditions(mixed lubrication regime,lubricant depletion,and misalignment)are recreated.It is shown that the cage IAS is dependent on the lubrication regime and is sensitive to misalignment.The AE signal is also used to evaluate the lubrication regime.Experimental results suggest that the proposed technique can be used as a condition monitoring tool in industrial environments to detect abnormal REB conditions that may lead to premature failure.展开更多
A commercial Al-Mg alloy was subjected to equal channel angular pressing of 4 passes with and without postrolling, and the effects of post-rolling on the deformation characteristics of the alloy at 723 K were examined...A commercial Al-Mg alloy was subjected to equal channel angular pressing of 4 passes with and without postrolling, and the effects of post-rolling on the deformation characteristics of the alloy at 723 K were examined. Post-rolling was found to influence the deformation behavior significantly. The deformation behavior of the alloy processed only by equal channel angular pressing was characterized by (a) localized deformation indicated by severe surface prominence and depression, (b) the strain rate sensitivity of 0.33, and (c) moderate high strain rate superplastic elongations. By contrast, that of the alloy processed by equal channel angular pressing and post-rolling (70 % thickness reduction) was manifested by (a) uniform deformation associated with grain boundary sliding throughout the sample, (b) a sigmoidal behavior showing the strain rate sensitivity of 0.45 at the intermediate strain rates in the logarithmic stress-strain rate curve, and (c) very large high strain rate superplastic elongations.展开更多
基金Project(U2202255)supported by the National Natural Science Foundation of ChinaProject(2024JJ2076)supported by the Hunan Provincial Natural Science Foundation of ChinaProject(2023Z092)supported by the Key Technology Research Program of Ningbo,China。
文摘In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and properties of the alloy were investigated in detail.The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing(ECAP)and rolling had good comprehensive properties after aging at 400℃.The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa,with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS,respectively.ECAP and cryogenic rolling introduced high density dislocations,leading to the inhibition of the softening effects and refinement of the grains.After a long time aging at 400℃,the alloy exhibited ultra-high strength with obvious increasing electrical conductivity.The high strength was attributed to the synergistic effect of work hardening,grain refinement strengthening and precipitation strengthening.The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.
基金financially supported by the Fundamental Research Funds for the Central Universities(Grant Nos.N160704003,N170708020,N2107007).
文摘Angular rolling technology can overcome the size limitation of plate mill equipment and product heavy steel plate with large unit weight or improve the production efficiency of small width spreading ratio product.With the DEFORM software,the numerical simulation study of the angular rolling process was carried out,and the relation laws of the width,rolling force and strain of the rolled piece under different angular rolling process conditions were obtained.The simulation results show that with the rotation angle increasing,the width of the rolled piece increases.Comparing with the conventional rolling process,the rolling force changes gradually during the biting and throwing stage of the angular rolling pass.With the rotation angle increasing,both the equivalent strains in the thickness direction and in the width direction gradually increase.According to the pattern and dimension's changing formula in the double-pass angular rolling process,the prediction model of angle,reduction and width spreading is built.The opening value of side guide is set for the rotation angle controlling.For one 5000 mm heavy plate mill,the automation control system was modified,and the angular rolling technology was applied online.The absolute deviation of target width does not exceed±20 mm and the relative deviation does not exceed 1%.The large unit weight plate that cannot be rolled with traditional process,can be produced now,and the annual output increases by 10000 t.
基金Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province(20210046)(jiēbǎng guàshuài)“Open Competition”Project:Preparation Technology and Product Development of Key New Materials for 5G Communication。
基金This work was funded by the National Natural Science Foundation of China(Nos.52175119 and 61633001).The authors are also grateful for the support of Xi’an Aerospace Propulsion Institution(China Aerospace Science and Technology Corporation).
文摘Sliding and spinning behaviors significantly affect the performance of rolling bearings,especially for dry-lubricated bearings,micro and macro sliding may lead to increased wear of the solid lubricating film.A unified rolling contact tribology analytical model is proposed for dry-lubricated angular contact ball bearings(ACBBs)considering the extreme conditions including high combined loads and rolling contact effects.A comprehensive solution framework is proposed to ensure the robustness of the model under different loading conditions.Equilibrium equations are solved to study the effects of friction coefficients,rotating speeds,and combined loads on the skidding and spinning characteristics of the ACBB.The results show that the rolling contact effects and combined loads significantly affect the skidding and spinning performance of the ACBB.Further analysis reveals that the skidding mechanism is related to the interaction between ball kinematical motion and traction forces.The developed analytical model is proved to more accurately predict the bearing kinematical and tribological behavior as it discards the raceway control hypothesis and considers the macro/micro-slipping,creepage,and self-spinning motions of the ball,which is validated using both the existing pure axial loading dry-lubricated ACBB model and the classical Jones–Harris model.The study would provide some guidance for the structure and lubrication design of dry-lubricated ACBBs.
文摘In this paper,we present an alternative technique for detecting changes in the operating conditions of rolling element bearings(REBs)that can lead to premature failure.The developed technique is based on measuring the kinematics of the bearing cage.The rotational motion of the cage is driven by traction forces generated in the contacts of the rolling elements with the races.It is known that the cage angular frequency relative to shaft angular frequency depends on the bearing load,the bearing speed,and the lubrication condition since these factors determine the lubricant film thickness and the associated traction forces.Since a large percentage of REB failures are due to misalignment or lubrication problems,any evidence of these conditions should be interpreted as an incipient fault.In this paper,a novel method for the measurement of the instantaneous angular speed(IAS)of the cage is developed.The method is evaluated in a deep groove ball bearing test rig equipped with a cage IAS sensor,as well as a custom acoustic emission(AE)transducer and a piezoelectric accelerometer.The IAS of the cage is analyzed under different bearing loads and shaft speeds,showing the dependence of the cage angular speed with the calculated lubricant film thickness.Typical bearing faulty operating conditions(mixed lubrication regime,lubricant depletion,and misalignment)are recreated.It is shown that the cage IAS is dependent on the lubrication regime and is sensitive to misalignment.The AE signal is also used to evaluate the lubrication regime.Experimental results suggest that the proposed technique can be used as a condition monitoring tool in industrial environments to detect abnormal REB conditions that may lead to premature failure.
文摘A commercial Al-Mg alloy was subjected to equal channel angular pressing of 4 passes with and without postrolling, and the effects of post-rolling on the deformation characteristics of the alloy at 723 K were examined. Post-rolling was found to influence the deformation behavior significantly. The deformation behavior of the alloy processed only by equal channel angular pressing was characterized by (a) localized deformation indicated by severe surface prominence and depression, (b) the strain rate sensitivity of 0.33, and (c) moderate high strain rate superplastic elongations. By contrast, that of the alloy processed by equal channel angular pressing and post-rolling (70 % thickness reduction) was manifested by (a) uniform deformation associated with grain boundary sliding throughout the sample, (b) a sigmoidal behavior showing the strain rate sensitivity of 0.45 at the intermediate strain rates in the logarithmic stress-strain rate curve, and (c) very large high strain rate superplastic elongations.
