钻柱正弦屈曲对裂纹疲劳寿命的影响

Effect of sinus buckling on crack fatigue life in rotating drilling

针对钻进过程中由于屈曲段旋转产生的离心力导致的附加弯曲应力对该段的裂纹扩展与管柱寿命产生的影响,计算了屈曲段以ω角速度旋转时所产生的离心力,利用纵横弯曲梁理论求得了在该离心力作用下屈曲段所产生的最大附加弯矩和最大附加弯曲应力,并结合裂纹扩展理论,建立了考虑管柱旋转状态下屈曲对裂纹扩展寿命影响的模型,得出了以ω旋转的临界屈曲段裂纹扩展速率的解析表达式。算例表明,在钻进中由于发生正弦屈曲而产生的附加弯曲应力对该管柱上的裂纹扩展速率及其疲劳寿命有显著影响,在评价裂纹疲劳寿命时,不能忽视屈曲对裂纹寿命的影响。

Centrifugal force will be generated in the buckling interval of drill string during drilling, so additional bending stress will be yielded in the same section. This additional bending stress has great effect on string life and crack propagation. So the centrifugal force generated from rotation of the buckling interval with angular speed ω is calculated. The maximum additional bending moment and maximum additional bending stress are presented based on the beam - column theory. Combined with the crack propagation theory, a model about the effect of buckling on the crack propagation life considering the effect of string buckling is established, the analytic expression of crack propagation speed of critical buckling intervals with angular speed ω is obtained. Case study shows that the additional bending stress caused by sine buckling during drilling exerts great effect on crack fatigue life and crack propagation speed of buckled strings. The effect of buckling cannot be neglected while evaluating crack fatigue life.