Experimental and theoretical evaluations of the effect between diameter-to-thickness ratio and curvature-rate on the stability of circular tubes under cyclic bending

This paper presents the experimental and theoretical results of the effect between diameter-to-thickness ratio (D/t ratio) and curvature-rate on the response and collapse of circular tubes subjected to cyclic bending. In experimental tests, four different D/t ratios of circular tubes and three different controlled curvature-rates were used. It was observed from experimental data that if circular tubes with a certain D/t ratio were used to test by three different curvature-rates, three parallel straight lines can be seen from the relationship between the controlled curvature and the number of cycles to produce buckling in log-log scale. In addition, it was also found that the distances among three parallel straight lines for the tubes with a higher D/t ratio are wider than that with a lower D/t ratio. Finally, theoretical formulations proposed by Lee and Pan((1)) and Lee, et al.((2)) were combined and modified so that it can be used for simulating the relationship between the controlled curvature and the number of cycles to produce buckling for circular tubes with different D/t ratios subjected to cyclic bending with different curvature-rates. The theoretical simulation was compared with the experimental data. Good agreement between the experimental and theoretical results has been achieved.