The majority of this research has concentrated on developing the self-support friction stir welding（SSFSW） tool which consists of a big concave upper shoulder and a small convex lower shoulder, and procedures for ma...The majority of this research has concentrated on developing the self-support friction stir welding（SSFSW） tool which consists of a big concave upper shoulder and a small convex lower shoulder, and procedures for making reliable welds in aluminum hollow extrusion. The 5-mm-thick 6082-T6 aluminum alloy was self-support friction stir welded at a constant tool rotation speed of 800 r/min. The effect of welding speed on microstructure and mechanical properties was investigated. The results of transverse tensile test indicated that the tensile strength of joints increased and the elongation decreased with increasing welding speed. The whole values of microhardness of SSFSW joints increased with increasing welding speed from 10 to 200 mm/min. The defectfree joints were obtained at lower welding speeds and the tensile fracture was located at the heat-affected zone（HAZ） adjacent to the thermo-mechanically affected zone（TMAZ） on the advancing side. The investigation of the flow pattern of the softened metal around the SSFSW tool revealed that the flow pattern of the softened metal was driven by two shoulders and the stir pin. The failure of specimens in tension presented the ductile fracture mode.展开更多
The elastic support/dry friction damper is a type of damper which is used for active vibration control in a rotor system.To establish the analytical model of this type of damper,a two-dimensional friction model-ball/p...The elastic support/dry friction damper is a type of damper which is used for active vibration control in a rotor system.To establish the analytical model of this type of damper,a two-dimensional friction model-ball/plate model was proposed.By using this ball/plate model,a dynamics model of rotor with elastic support/dry friction dampers was established and experimentally verified.Moreover,the damping performance of the elastic support/dry friction damper was studied numerically with respect to some variable parameters.The numerical study shows that the damping performance of the elastic support/dry friction damper is closely related to the stiffness distribution of the rotor-support system,the damper location,the pressing force between the moving and stationary disk,the friction coefficient,the tangential contact stiffness of the contact interface,and the stiffness of the stationary disk.In general,the damper should be located on an elastic support which has a large vibration amplitude in order to achieve a better damping performance,and the more vibration energy in this elastic support concentrates,the better performance of the damper will be.The larger the tangential contact stiffness of the contact interface,and the stiffness of the stationary disk are,the better performance of the damper will be.There will be an optimal value of the friction force at which the damper performs best.展开更多
利用一种电磁型主控式干摩擦阻尼器(active magnetic dry friction damper,AMDFD)来改变支承的阻尼,以实现对航空发动机转子系统支承结构外传振动的有效控制。在传统的双转子系统动力学模型基础上,建立了能够表征支承外传振动的AMDFD-...利用一种电磁型主控式干摩擦阻尼器(active magnetic dry friction damper,AMDFD)来改变支承的阻尼,以实现对航空发动机转子系统支承结构外传振动的有效控制。在传统的双转子系统动力学模型基础上,建立了能够表征支承外传振动的AMDFD-双转子-轴承座动力学模型;采用转速区间开关控制器和无模型自适应控制器,对AMDFD抑制转子支承结构外传振动的有效性进行了仿真分析,并阐明了AMDFD抑制支承结构外传振动的内在机理。在搭建的AMDFD-双转子系统试验台上,进行了双转子系统加速通过多阶临界转速区时支承结构外传振动的主动控制试验。结果表明,利用转速区间的开关控制器和无模型自适应控制器,AMDFD能够有效地降低各支承位置在各阶临界转速区的外传振动,降低幅度均超过了52%。展开更多
基金supported by the National Natural Science Foundation of China (Nos. 50904020 and 50974046)the Fundamental Research Funds for the Central Universities (No. HIT. NSRIF. 2012007)
文摘The majority of this research has concentrated on developing the self-support friction stir welding（SSFSW） tool which consists of a big concave upper shoulder and a small convex lower shoulder, and procedures for making reliable welds in aluminum hollow extrusion. The 5-mm-thick 6082-T6 aluminum alloy was self-support friction stir welded at a constant tool rotation speed of 800 r/min. The effect of welding speed on microstructure and mechanical properties was investigated. The results of transverse tensile test indicated that the tensile strength of joints increased and the elongation decreased with increasing welding speed. The whole values of microhardness of SSFSW joints increased with increasing welding speed from 10 to 200 mm/min. The defectfree joints were obtained at lower welding speeds and the tensile fracture was located at the heat-affected zone（HAZ） adjacent to the thermo-mechanically affected zone（TMAZ） on the advancing side. The investigation of the flow pattern of the softened metal around the SSFSW tool revealed that the flow pattern of the softened metal was driven by two shoulders and the stir pin. The failure of specimens in tension presented the ductile fracture mode.
基金supported by the National Natural Science Foundation of China(No.51405393)
文摘The elastic support/dry friction damper is a type of damper which is used for active vibration control in a rotor system.To establish the analytical model of this type of damper,a two-dimensional friction model-ball/plate model was proposed.By using this ball/plate model,a dynamics model of rotor with elastic support/dry friction dampers was established and experimentally verified.Moreover,the damping performance of the elastic support/dry friction damper was studied numerically with respect to some variable parameters.The numerical study shows that the damping performance of the elastic support/dry friction damper is closely related to the stiffness distribution of the rotor-support system,the damper location,the pressing force between the moving and stationary disk,the friction coefficient,the tangential contact stiffness of the contact interface,and the stiffness of the stationary disk.In general,the damper should be located on an elastic support which has a large vibration amplitude in order to achieve a better damping performance,and the more vibration energy in this elastic support concentrates,the better performance of the damper will be.The larger the tangential contact stiffness of the contact interface,and the stiffness of the stationary disk are,the better performance of the damper will be.There will be an optimal value of the friction force at which the damper performs best.
文摘利用一种电磁型主控式干摩擦阻尼器(active magnetic dry friction damper,AMDFD)来改变支承的阻尼,以实现对航空发动机转子系统支承结构外传振动的有效控制。在传统的双转子系统动力学模型基础上,建立了能够表征支承外传振动的AMDFD-双转子-轴承座动力学模型;采用转速区间开关控制器和无模型自适应控制器,对AMDFD抑制转子支承结构外传振动的有效性进行了仿真分析,并阐明了AMDFD抑制支承结构外传振动的内在机理。在搭建的AMDFD-双转子系统试验台上,进行了双转子系统加速通过多阶临界转速区时支承结构外传振动的主动控制试验。结果表明,利用转速区间的开关控制器和无模型自适应控制器,AMDFD能够有效地降低各支承位置在各阶临界转速区的外传振动,降低幅度均超过了52%。
