Multiaxial Cyclic Ratcheting in Coiled Tubing—Part II: Experimental Program and Model Evaluation

Abstract

An experimental program was conducted to evaluate the plasticity model proposed in a separate paper (Part I). Constant pressure, cyclic bend-straighten tests were performed to identify material parameters required by the analytical model. Block pressure, bend-straighten tests were conducted to evaluate the proposed model. Experiments were performed on full-size coiled tubing samples using a specialized test machine. Two commonly used coiled tubing materials and four specimen sizes were subjected to load histories consisting of bending-straightening cycles with varying levels of internal pressure. It was observed that cyclic ratcheting rates can be reversed without reversing the mean stress, i.e., diametral growth of coiled tubing can be followed by diametral shrinkage even when the internal pressure is kept positive, depending on the loading history. This material behavior is explained in the context of the new theory. The correlation between the predictions and the test data is very good. [S0094-4289(00)00502-8]