The behavior of rolling contact fatigue (RCF) of medium carbon bainitic back-up roll steel was investigated under its actual work conditions. A kind of asperity-scale surface originated cracks, which is lying parallel...The behavior of rolling contact fatigue (RCF) of medium carbon bainitic back-up roll steel was investigated under its actual work conditions. A kind of asperity-scale surface originated cracks, which is lying parallel or at an acute angle to the surfaces, initiated after unidirectional plastic flow of the material in thin surface layer had occurred. Theoretical analysis indicates that they nucleate due to plastic ratcheting induced by asperity contact stresses, and consequently are named as ratcheting cracks. After nucleating and initially propagating, they arrest at some depth and resume propagating till about 70%-80% of the RCF failure life by initially turning parallel to contact surfaces. Their behavior of initiation and propagation is confined to a thin layer prior to the formation of surface distress. According to the critical principle of the preventive grinding strategy, removing the asperity influenced surface layer at about 70%-80% of the RCF failure life can effectively prevent the ratcheting cracks from developing into surface distress, which can lead to the formation of macro-RCF failure soon.展开更多
The 3-D traction field in the pressure screw-pair of a 3 500 heavy and mediumplate mill press down system is successfully calculated by applying the 3-D frictional contactmultipole-BEM and the corresponding program th...The 3-D traction field in the pressure screw-pair of a 3 500 heavy and mediumplate mill press down system is successfully calculated by applying the 3-D frictional contactmultipole-BEM and the corresponding program that has been developed. The computing results show themedium diameter orientation is unreliable, especially under the interference of an outer forcecouple. Under such working conditions, the circumferential traction distribution on the screw teethis extremely uneven, which is the main reason for the destruction and short life time ofscrew-pairs. When utilizing the same precision (the relative tolerance is 10X10^(-5)), themultipole-BEM uses almost the same CPU time as used by the FEM, but the needed computer memory sizeis only one eightieth of that needed by the FEM (10 MB vs. 800 MB). The multipole-BEM is well suitedfor computing large-scale engineering problems.展开更多
基于物质点方法(material point method,MPM)理论框架,提出了处理饱和多孔介质与固体间动力接触问题的新方法。其中饱和多孔介质的动力学响应通过文献[1]中发展的耦合物质点方法进行分析,单相固体的力学行为由传统单相物质点方法进行预...基于物质点方法(material point method,MPM)理论框架,提出了处理饱和多孔介质与固体间动力接触问题的新方法。其中饱和多孔介质的动力学响应通过文献[1]中发展的耦合物质点方法进行分析,单相固体的力学行为由传统单相物质点方法进行预测。通过本文提出的接触算法使二者相结合,在保证饱和多孔介质与固体间不存在相互穿透的前提下,允许饱和多孔介质与固体间的相互滑动,以预测整个接触/碰撞系统的动力学响应。同时进行了数值算例计算,通过算例验证了此方法的正确性,展示了此方法有效性。展开更多
文摘The behavior of rolling contact fatigue (RCF) of medium carbon bainitic back-up roll steel was investigated under its actual work conditions. A kind of asperity-scale surface originated cracks, which is lying parallel or at an acute angle to the surfaces, initiated after unidirectional plastic flow of the material in thin surface layer had occurred. Theoretical analysis indicates that they nucleate due to plastic ratcheting induced by asperity contact stresses, and consequently are named as ratcheting cracks. After nucleating and initially propagating, they arrest at some depth and resume propagating till about 70%-80% of the RCF failure life by initially turning parallel to contact surfaces. Their behavior of initiation and propagation is confined to a thin layer prior to the formation of surface distress. According to the critical principle of the preventive grinding strategy, removing the asperity influenced surface layer at about 70%-80% of the RCF failure life can effectively prevent the ratcheting cracks from developing into surface distress, which can lead to the formation of macro-RCF failure soon.
基金This project is supported by National Natural Science Foundation of China(No.50075075) National "Ten-Five" Science and Technology Project of China(No.ZZ 01-13A-02-02-03). J
文摘The 3-D traction field in the pressure screw-pair of a 3 500 heavy and mediumplate mill press down system is successfully calculated by applying the 3-D frictional contactmultipole-BEM and the corresponding program that has been developed. The computing results show themedium diameter orientation is unreliable, especially under the interference of an outer forcecouple. Under such working conditions, the circumferential traction distribution on the screw teethis extremely uneven, which is the main reason for the destruction and short life time ofscrew-pairs. When utilizing the same precision (the relative tolerance is 10X10^(-5)), themultipole-BEM uses almost the same CPU time as used by the FEM, but the needed computer memory sizeis only one eightieth of that needed by the FEM (10 MB vs. 800 MB). The multipole-BEM is well suitedfor computing large-scale engineering problems.
文摘基于物质点方法(material point method,MPM)理论框架,提出了处理饱和多孔介质与固体间动力接触问题的新方法。其中饱和多孔介质的动力学响应通过文献[1]中发展的耦合物质点方法进行分析,单相固体的力学行为由传统单相物质点方法进行预测。通过本文提出的接触算法使二者相结合,在保证饱和多孔介质与固体间不存在相互穿透的前提下,允许饱和多孔介质与固体间的相互滑动,以预测整个接触/碰撞系统的动力学响应。同时进行了数值算例计算,通过算例验证了此方法的正确性,展示了此方法有效性。
