Abstract: This paper proved that the fatigue limit curve of the diagram is very safety by the study of the recommended-modified Goodmen-stress diagram of the API RP 11BR.According to the calculation of its allowable safety coefficient,the maximum allowable stress in the diagram was reduced with the increasing of component of the alternating stresses,it met the requirement of the allowable stress of the sucker rod,and met the conventional principle of the fatigue design.The paper suggested that the work range of the tensile safety of the recommended API diagram be extended to the work range of the tensile-compress safety that the stress ratio r is less than 0~-1,so as to calculate the parameters of the down section of the sucker rod.It was presented that the minimum fatigue limit was regarded as the allowable stress when the stress ratio r of the down section of the sucker rod is less than -1,and its stress strength condition is σ_min≥[σ_min].

Key words: sucker rod, stress ratio, fatigue limit, fatigue strength, allowable safety coefficient

摘要： 研究APIRP11BR推荐的修正的古德曼应力图后得出:该图的疲劳极限曲线是一条偏于安全的疲劳极限图线;对许用安全系数的计算表明,该图推荐的最大许用应力随交变应力中的交变分量的增大而减小,符合抽油杆对许用应力的要求,对应的许用安全系数符合常规疲劳设计的取值原则,是合理、科学的;建议将API推荐图上的拉拉载荷安全工作区扩大到应力比r<0～-1的拉压载荷工作区,以用于对抽油杆柱下部杆段的计算;当下部杆段的应力比r<-1时,建议以最小疲劳极限作为许用应力,其强度条件为σ_min≥[σ_min]。

关键词: 抽油杆, 应力比, 疲劳极限, 疲劳强度, 许用安全系数