Effect of sinus buckling on crack fatigue life in rotating drilling

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.