Seyed Amirreza Shamsdini - Institute of Mechanics, Iranian Space Research Center, Iranian Space Agency
Ali Nayebi - Mechanical engineering School, Shiraz University

It is useful to have knowledge of plastic deformation after cyclic bending happens on coiled tubing. In this article we analyze the elastic-plastic deformation in tubes with internal pressure and cyclic bending which is applicable in coiled tubing. With the aid of the Prager kinematic hardening model and the von-Mises yield criteria we first calculated the elastic loading region for various pressure and bending, then the plastic deformation is measured. The thin walled surface is divided into circumferential elements. The material constants are selected from the ۴۱۳۰ alloy steel data. Plastic strains are calculated with the return mapping method. For no plastic deformation history for the material, the theoretical calculations result in a yield surface in the curvature-pressure surface with an ellipse shape. The ellipse is inclined and this load interactiondiagram is known as the Bree diagram. The internal region of the ellipse is the region in which all deformations are elastic. For the Prager model the stabilization of the strain is observed and the model predicts plastic shakedown. With increasing the curvature the plastic shakedown occurs in earlier loading cycles.

Ratcheting, coiled tubing, kinematic hardening, cyclic bending