In this paper, the response of sharp-notched circular tubes with notch depths of 0.2, 0.4, 0.6, 0.8 and 1.0 mm subjected to bending creep and relaxation are investigated. The bending creep or relaxation is to bend the tube to a desired moment or curvature and hold that moment or curvature constant for a period of time. From the experimental result of bending creep, the creep curvature and ovalization increase with time. In addition, higher held moment leads to the higher creep curvature and ovalization of the tube's cross-section. From the experimental result for bending relaxation, the bending moment rapidly decreases with time and becomes a steady value. As for the ovalization, the amount increases a little with time and gradually becomes a steady value. Due to the constant ovalization caused by the constant curvature under bending relaxation, the tube does not buckle. Finally, the formulation proposed by Lee and Pan (2002) is modified for simulating both the creep curvature-time relationship in the first stage under bending creep and the relaxation moment-time relationship under bending relaxation for sharp-notched circular tubes with different notch depths. Through comparing with the experimental finding, the theoretical analysis can reasonably describe the experimental result. Keywords IntroductionThe circular tube components, which are used in several industrial applications such as offshore pipelines, platforms in offshore deep water, tubular components in nuclear reactors, etc., are often subjected to bending. It is well known that the ovalization of the tube cross-section is observed when a circular tube is subjected to bending. If the bending moment or curvature increases, the ovalization also increases. Increase in ovalization causes a progressive reduction in the bending rigidity, which can result in buckling of the tube components. Therefore, the study of the response of circular tubes subjected to bending is of importance in many industrial applications.In early stage, Kyriakides and his co-workers designed and constructed a tube cyclic bending machine, and conducted a series of experimental and theoretical investigations. Shaw and Kyriakides (1985) investigated the inelastic behavior of 6061-T6 aluminum and 1018 steel tubes subjected to cyclic bending. Kyriakides and Shaw (1987) extended the analysis of 6061-T6 aluminum and 1018 steel tubes to the stability conditions under cyclic bending. Corona and Kyriakides (1988) investigated the stability of 304 stainless steel tubes subjected to combined bending and external pressure. Corona and Vaze (1996) studied the response, buckling and collapse of long, thin-walled seamless steel square tubes under bending. Vaze and Corona (1998) experimentally investigated the elastic-plastic degradation and collapse of steel tubes with square cross-sections under cyclic bending. Corona et al. (2006) used a set of bending experiments to conduct on aluminum alloy tubes for investigating the yield anisotropy effects on the buckling. Response of sharp-notched ci...

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The elasto-plastic behavior of a titanium alloy tube subjected to cyclic bending was investigated. The curvature-ovalization measurement apparatus, designed by , was used for conducting the curvature-controlled experiment on the tubular specimen. The results reveal that the magnitudes of the bending moment and ovalization of the tube cross-section increase when the tube curvature increases. In addition, the ovalization of the tube cross-section increases in ratcheting manner when the number of bending cycles increase. Finally, the endochronic formulation, which was proposed by Pan and Leu (1997), is used to investigate the elasto-plastic behavior of titanium alloy tube under cyclic bending. Reasonable agreement between theoretical and experimental results is achieved.

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