A new experimental apparatus was set up to investigate the actual friction characteristics on the basis of speed control of the serve system.A modified friction model was proposed due to real time varying deformation ...A new experimental apparatus was set up to investigate the actual friction characteristics on the basis of speed control of the serve system.A modified friction model was proposed due to real time varying deformation resistance.The approach to identify the parameters of comprehensive friction behaviors based on the modified model was proposed and applied to the forging press.The impacts on parameters which the external load had were also investigated.The results show that friction force decreases with velocity in the low velocity regime whereas the friction force increases with the velocity in the high velocity regime under no external load.It is also shown that the Coulomb friction force,the maximum static friction force and the vicious friction coefficient change linearly with the external load taking the velocity at which the magnitude of the steady state friction force becomes minimum as the critical velocity.展开更多
Equal channel angular pressing （ECAP） is an effective thermo-mechanical process to make ultrafine grains. An investigation was carried out on the friction stir welding （FSW） of ECAPed AZ31 magnesium alloys with a ...Equal channel angular pressing （ECAP） is an effective thermo-mechanical process to make ultrafine grains. An investigation was carried out on the friction stir welding （FSW） of ECAPed AZ31 magnesium alloys with a thickness of 15 mm. For different process parameters, the optimum FSW conditions of ECAPed AZ31 magnesium alloys were examined. The basic characterization of weld formation and the mechanical properties of the joints were discussed. The results show that the effect of welding parameters on welding quality was evident and welding quality was sensitive to welding speed. Sound joints could be obtained when the welding speed was 37.5 mm/min and the rotation speed of the stir tool was 750 r/min. The maximum tensile strength （270 MPa） of FSW was 91% that of the base materials. The value of microhardness varied between advancing side and retreating side because of the speed field near the pin of the stir tool, which weakened the deformed stress field. The value of microhardness of the welding zone was lower than that of the base materials. The maximum value was located near the heat-affected zone （HAZ）. Remarkable ductile character was observed from the fracture morphologies of welded joints.展开更多
基金Project(51005251)supported by the National Natural Science Foundation of ChinaProject(2011CB706802)supported by the National Basic Research Development Program of China(973 Program)
文摘A new experimental apparatus was set up to investigate the actual friction characteristics on the basis of speed control of the serve system.A modified friction model was proposed due to real time varying deformation resistance.The approach to identify the parameters of comprehensive friction behaviors based on the modified model was proposed and applied to the forging press.The impacts on parameters which the external load had were also investigated.The results show that friction force decreases with velocity in the low velocity regime whereas the friction force increases with the velocity in the high velocity regime under no external load.It is also shown that the Coulomb friction force,the maximum static friction force and the vicious friction coefficient change linearly with the external load taking the velocity at which the magnitude of the steady state friction force becomes minimum as the critical velocity.
文摘Equal channel angular pressing （ECAP） is an effective thermo-mechanical process to make ultrafine grains. An investigation was carried out on the friction stir welding （FSW） of ECAPed AZ31 magnesium alloys with a thickness of 15 mm. For different process parameters, the optimum FSW conditions of ECAPed AZ31 magnesium alloys were examined. The basic characterization of weld formation and the mechanical properties of the joints were discussed. The results show that the effect of welding parameters on welding quality was evident and welding quality was sensitive to welding speed. Sound joints could be obtained when the welding speed was 37.5 mm/min and the rotation speed of the stir tool was 750 r/min. The maximum tensile strength （270 MPa） of FSW was 91% that of the base materials. The value of microhardness varied between advancing side and retreating side because of the speed field near the pin of the stir tool, which weakened the deformed stress field. The value of microhardness of the welding zone was lower than that of the base materials. The maximum value was located near the heat-affected zone （HAZ）. Remarkable ductile character was observed from the fracture morphologies of welded joints.
