The Influence of Diameter-to-thickness Ratios on the Response and Failure for Locally-dented Circular Tubes Submitted to Cyclic Bending

This paper describes the cyclic bending response and failure of 6061-T6 aluminum alloy locally-dented tubes (abbreviation: 6061-T6 LDT) with different diameter-to-thickness ratios (abbreviation: D _o/t ratio) of 16.5, 31.0 and 60.0. A small lateral local dent was created on the tube using a simple technique. A tube having a dent depth from very shallow to about 2.4 times the thickness of the tube wall is considered. From the first bending cycle, the moment-curvature relationship depicts a closed and stable loop. Due to small and localized dents, dent depth shows very small influence on its relationship. But, as the number of bending cycle increases, the ovalization-curvature relationship shows an increase and a ratchet-like distribution. However, the dent depth shows a dramatic effect to this relationship. Furthermore, for a certain D _o/t ratio, five non-paralleled straight lines of five different dent depths were found for the controlled curvature-number of cycles required to ignite failure relationship on a log-log scale. Finally, an empirical formula was introduced to describe the aforementioned relationship. As a result, the experimental and analytical data were found to agree well.