ABSTRACT--In this paper, the authors report the design and construction of a new measurement apparatus, along with the result of its testing. This apparatus can be placed at the midspan of the circular tube specimen and is suitable for simultaneous experimental determinations of the tube curvature and ovalization of the tube cross section. For testing the newly designed apparatus, the tube specimen of AISI 304 stainless steel was bent cyclically. It has been shown that the actual curvature and ovalization of the circular tube subjected to bending can be directly measured by the apparatus.
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.
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