Multiaxial cyclic ratcheting in coiled tubing - Part II: Experimental program and model evaluation

An experimental program was conducted to evaluate the plasticity model prop osed in a separate paper (Part I). Constant pressure, cyclic bend-straighte n tests were performed to identify material parameters required by the anal ytical model. Block pressure, bend-straighten tests were conducted to evalu ate the proposed model. Experiments were performed on full-size coiled tubi ng samples using a specialized test machine. Two commonly sued coiled tubin g materials and four specimen sizes were subjected to load histories consis ting of bending-straightening cycles with varying levels of internal pressu re. It was observed that cyclic ratcheting rates can be reversed without re versing the mean stress, i. e., diametral growth of coiled tubing can be fo llowed by diametral shrinkage even when the internal pressure is kept posit ive, depending on the loading history. This material behavior is explained in the context of the new theory. The correlation between the predictions a nd the test data is very good. [S0094-4289(00)00502-8].