Collapse of elliptical-notched circular tubes under cyclic bending

In this paper, an experimental investigation of the response and collapse of elliptical-notched tubes subjected to cyclic bending is discussed. It was found from moment-curvature curves that the loops show cyclic hardening and gradually steady after a few cycles. The ovalization-curvature curves show an unsymmetrical, ratcheting and increasing manner with the number of cycles. Based on the experimental relationship between the controlled curvature and the number of cycles necessary to produce buckling, the empirical formulation proposed by Kyriakides and Shaw in 1987 was modified for simulating the aforementioned relationship. In addition, it was found that the experimental curve of the ovalization and the number of cycles could be divided into three stages. The empirical relationship proposed by Chang and Pan in 2009 was modified for simulating the aforementioned curve of the initial and secondary stages. It has been shown that the simulations were in good agreement with the experimental data.