Mean moment effect on sharp-notched circular tubes under cyclic bending

This study discusses an experimental investigation of the effect of the mean moment on the response and collapse of sharp-notched circular tubes subjected to cyclic bending. To highlight the influence of the mean moment effect, five different moment ratios r (minimum moment / maximum moment) were experimentally investigated. We found that the moment-curvature loop gradually shrinks, and stabilizes after a few cycles for r = -1. However, the moment-curvature loop exhibits ratcheting and increases with the number of cycles for r not equal -1. In addition, the ovalization-curvature curve shows unsymmetrical, ratcheting and increasing manner with the number of cycles for any r. Finally, the empirical formulation proposed by Chang et al. [1] was modified to simulate the relationship between the controlled moment range and the number of cycles necessary to produce buckling. The results of the experimental investigation and the simulation were in good agreement with each other.