Coiled tubing is a long, continuous string of steel tubing that is used in the oil well drilling and servicing industry. Bending strains imposed on coiled tubing as it is deployed and retrieved from a well are considerably into the plastic regime and can be as high as 3 percent. Progressive growth of tubing diameter occurs when tubing is cyclically bent-straightened under constant internal pressure, regardless of the fact that the hoop stress imposed by typical pressure levels is well below the material’s yield strength. A new incremental plasticity model is proposed in this study that can predict multiaxial cyclic ratcheting in coiled tubing more accurately than the conventional plasticity models. A new hardening rule is presented based on published experimental observations. The model also implements a new plastic modulus function. The predictions based on the new theory correlate well with experimental results presented in Part II of this paper. Some previously unexpected trends in coiled tubing deformation behavior were observed and correctly predicted using the proposed model. [S0094-4289(00)00402-3]
Multiaxial Cyclic Ratcheting in Coiled Tubing—Part I: Theoretical Modeling
Contributed by the Materials Division for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received by the Materials Division November 19, 1998; revised manuscript received September 21, 1999. Associate Technical Editor: H. Sehitoglu.
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Rolovic, R., and Tipton, S. M. (September 21, 1999). "Multiaxial Cyclic Ratcheting in Coiled Tubing—Part I: Theoretical Modeling ." ASME. J. Eng. Mater. Technol. April 2000; 122(2): 157–161. https://doi.org/10.1115/1.482781
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