Summary Coiled tubing is continuous thin-walled steel tubing several thousands of meters in length without screwed connections. Cyclic plastic-bending deformation occurs during tubing spooling on the reel and when passing through the gooseneck arc guide. The coupling effect of cyclic plastic bending and internal pressure causes coiled-tubing diametral growth and wall thinning (referred to as ratcheting). This paper presents a numerical algorithm to calculate the deformations of the diameter and wall thickness on the basis of the incremental plasticity theory and the principle of virtual work. It is shown that predictions with the algorithm correlate well with experimental results.

A study on the microscopic morphology of real-world polymer blends and its mechanism of change showed that the microscopic morphology of equiproportional mixtures gradually changed from a dense body structure to a network structure with the addition of the total polymer concentration up to 20%; the microscopic morphology of mixtures with different proportions was characterized by the most uniform network structure of equiproportional mixtures when the total polymer concentration was 20%. The polymer acts as a defoamer in the mixed system. In this paper, the relationship between the microscopic morphology of each mixture and the physicochemical behavior of the two polymer chains in the mixed system was investigated on the basis of the Aifantis strain gradient theory. Molecular polymer microscopic interface and multiscale failure analysis are proposed. It is shown that for the dihedral angle distribution of four consecutive coarse-grained particles, the peaks obtained from all atomic-scale simulation data are reproduced in the coarse-grained model simulations. The deviation is within 2.5% in most places, except for the local area where the deviation exceeds 5%. Therefore, we have achieved good results for large-scale failures.