钻柱涡动情况下疲劳损伤浅析

钻柱在井下工作环境恶劣,疲劳破坏是钻柱失效的主要形式。随着对钻柱工作环境的不断认识,理论和实践都证实疲劳破坏是一个累积的过程,疲劳寿命与钻柱在弯曲和扭转组合作用下的交变应力有关。建立了在涡动情况下钻柱的交变力学模型,分析了交变弯曲应力,应用形状改变对构件屈服区进行了渐进分析,扩展了线弹性断裂力学的应用范围,并用Forman模型预测了钻柱的疲劳寿命,使计算结果更加准确,引入疲劳损伤观点为钻柱使用安全性的判断增添了一种新方法,具有较好的应用前景。

Fatigue damage research for whirled drillstring

Due to the bad working conditions, fatigue damage becomes the main form of drillstring failure. With the increasing understandings of drillstring work environment, theory and practice proves that fatigue damage is a cumulative process, which is related to the flexural-torsional alternate bending stress acted on drillstring. The mechanical model of whirled drill-string is established, and the stress especially the alterative bending stress of the drill-string is analyzed in this paper. At the crack tip, the plastic deformation and the plastic zone correction is taken into account to broaden the applied scope of the liner-elastic mechanics in this paper. Moreover, the Forman fatigue life prediction model is used to predict the drillstring fatigue life, which makes the result better. Fatigue damage makes the safety coefficient of drilling string higher.