油杆疲劳裂纹扩展中的闭合约束模型研究.pdfVIP

抽油杆疲劳裂纹扩展中的闭合约束模型研究 摘 要 当前，世界各国陆上石油生产均以机械采油为主。抽油杆是油田机械采油中 的主要受力构件,在油井中服役时，由于承受交变载荷而发生的疲劳断裂是造成 油井事故的重要原因之一。调查研究表明，这种断裂事故大多是由于抽油杆存在 表面裂纹缺陷扩展引起的疲劳断裂或腐蚀疲劳断裂造成的。 复杂的载荷状况、苛刻的工作环境对抽油杆材料的疲劳、蠕变性能造成很大 的影响。因此避免抽油杆断裂，安全生产将变得尤为重要。 本文以镍基合金和粉末合金为试验研究对象，研究了厚度以及应力比对疲劳 裂纹扩展的影响，研究发现，室温条件下，当应力比 R 较小时，两种材料裂纹 扩展的厚度约束效应非常明显；然而当 R 较大时，在较低的应力强度因子幅值 时，厚度对疲劳裂纹扩展的影响并不大；应力比对疲劳裂纹扩展的影响非常明显， 同样的应力强度因子幅值条件下，应力比越大疲劳裂纹扩展越快，而且随着ΔK 的增大应力比的影响越明显。在疲劳裂纹扩展速率分析的基础上，利用国际上现 行的三维疲劳裂纹扩展闭合约束模型，Guo 与 Newman 模型进行了疲劳裂纹归一 化处理，对其中的关键问题进行了讨论。 关键词：抽油杆，疲劳断裂，应力强度因子，裂纹扩展速率，闭合约束 I 抽油杆疲劳裂纹扩展中的闭合约束模型研究 Abstract At present, mechanical oil extraction is the main method for land-based oil-producing, and so sucker rod may be the major stress component. Fatigue fracture, caused by the cycle load, is one of the substantial reasons leading to oil well accidents. From the foregoing investigations, it is found that it may be surface cracks emanating in sucker rod, which lead to the following fatigue fracture or corrosion fatigue, cause the failure of components. The sucker rod’s material weary and slow-changing performances are tremendously influenced by the complex load condition and the harsh working conditions. Hence it will be especially important to avoid sucker rod’s break and to ensure the safety in production. This article has studied how thickness as well as the stress ratio influences the fatigue crack growth. Under the condition of room temperature, when stress ratio R is less, the effects of thickness constraint are obvious for two different nickel based materials, however, when R is bigger,