中文摘要：

钻杆的疲劳失效是引发钻井井下事故的主要原因,因此有必要对钻杆的应力-疲劳寿命曲线进行试验研究。采用旋转弯曲疲劳试验机,研究了常用的S135和G105钻杆的疲劳性能;采用疲劳寿命对数正态分布模型,得出了任意存活率对应的应力-疲劳寿命曲线;采用直接外推法和2 m-1外推法将疲劳曲线延伸到长寿命区域,并将其外推结果与配对升降法试验结果进行了对比。升降法试验得出S135和G105钻杆的疲劳强度（存活率为99%,置信度为95%）分别为550.19 MPa和454.79 MPa;由直接外推存活率99%的曲线得到疲劳寿命为1.0×10^7时,S135和G105钻杆对应强度分别为510.23 MPa和402.01 MPa;由2 m-1外推法外推存活率99%的曲线得到疲劳寿命为1.0×10^7时,S135和G105钻杆对应强度分别为532.95 MPa和428.98 MPa。试验表明,2种外推方法得到的疲劳强度均低于试验值,2 m-1外推法得到的疲劳强度值更接近升降法试验值,因此推荐使用2 m-1外推法对概率-应力-疲劳寿命曲线进行外推来得到完整的疲劳寿命曲线。

英文摘要：

Drill pipe failure due to fatigue is the main cause of the oilfield drilling accidents,so it is necessary to study the stress-fatigue life curves of drill pipes.The fatigue performances of S135 and G105drill pipe materials were studied by using the rotating bending fatigue testing machine.The logarithmic normal distribution model was adopted to obtain the stress-fatigue life curves corresponding to any survival rates.The direct extrapolation and 2m-1index method were adopted to extend the fatigue curve into longlife area and the extrapolated fatigue results were compared with the up-and-down method results.The upand-down method showed that the fatigue strengths of S135 and G105drill pipes（survival rate was 99%and confidence level was 95%）were 550.19 MPa and 454.79 MPa respectively.The corresponding strengths of drill pipes S135 and G105were 510.23 MPa and 402.01 MPa respectively when the fatigue life obtained by the curve with direct extrapolation survival rate of 99% was 1.0×10^7,while the 2m-1method showed that when the curve of survival rate 99% obtained a fatigue life of 1.0×10^7,the drill pipe strengths were 532.95 MPa and 428.98 MPa respectively.The tests turned out that the fatigue strengths extrapolated by these two methods were both less than the test values.The fatigue strength value measured by the 2m-1index method was closer to the test value by up-and-down method,so the 2m-1index method was recommended to extrapolate the probability-stress-fatigue life curves so that a complete fatigue life curve could be obtained.