| Summary: | 碩士 === 國立成功大學 === 工程科學系碩博士班 === 95 === This thesis presents an experimental investigation on the mechanical behavior and buckling failure of circular tubes (316L and SUS 304 stainless steel tubes) with different outside and inside diameters subjected to cyclic bending. In this study, the tube bending machine and curvature-ovalization measurement apparatus were used to conduct the curvature-controlled cyclic bending to buckling test. Three different outside and inside diameters with three different outside-diameter / wall-thickness (Do/t) ratios of 316L and SUS 304 stainless steel tubes were tested. It can be observed from the experimental moment-curvature curves that the SUS 304 and 316L stainless steel tubes harden cyclically and become steady after a few cycles for curvature- controlled cyclic bending. As for the ovalization-curvature curve, the ovalization of the tube cross-section increases in a ratcheting manner with the number of cycles. Owing to the progressive accumulation of the ovalization of the tube cross-section during cyclic bending, the tubes buckle eventually. In addition, three almost parallel straight lines were observed from the relationship between the controlled curvature and the number of cycles to produce buckling for three different outside and inside diameters with three different Do/t ratios of steel tubes in the log-log scale. Finally, a theoretical formulation was proposed to simulate the relationship between the controlled curvature and the number of cycles to produce buckling for three different outside and inside diameters with three different Do/t ratios of circular tubes. When compared with the experimental data, the theoretical analysis can properly simulate the experimental result.
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