How deep drilling(oil, etc) avoids drill twisting on its axis? Wouldn’t kilometers long steel drills be akin to licorice?
In: 1257
The ability of the drill to resist twisting is enhanced by its geometry: a hollow pipe. The same amount of steel formed into a solid rod would be much less stiff (more strain per unit stress), and the difference between the stress in the center (zero) and the stress in the perimeter of a solid rod is much greater than the variation in stress of the pipe.
Differential stress will result in failure of the material if the stress is high enough to reach a plasticity point. A rod that’s stressed to the point of plastic deformation will snap because the outer portion is twisted and undergoes plastic deformation, while the center is not. For a pipe, even if you were to stress the pipe to the point of plastic deformation, so long as there’s sufficient weight on the pipe to keep it from collapsing, you’ll still have a pipe, as the stress on the inner portion and the outer portion of the pipe is nearly equal – you’d have a slightly twisted pipe.
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