This paper investigates the bending behavior of very high strength (VHS) circular steel tubes. The tested VHS tube has a normal yield stress of 1350 MPa and an ultimate strength of 1500 MPa. A total of 12 specimens, with the normal diameter ranging from 31.8 to 75 mm and the tube thickness between 1.6 and 2.0 mm, were tested. Large bending deflection was achieved for VHS tubes with the diameter to thickness ratio up to 24. Full plastic moment was reached for tubes with the section slenderness of 197 or less. New plastic slenderness limits of 117 and 153 were proposed based on the beam plastic rotation capacity of 4 and 3. A yield slenderness limit of 264 was proposed for VHS tubes.

Section slenderness limits of very high strength circular steel tubes in bending

Buckling life estimation of circular tubes under cyclic bending

The influence of the diameter-to-thickness ratio on the stability of circular tubes under cyclic bending

This paper presents the experimental result on the response and stability of thin walled tubes subjected to cyclic bending with different curvature-rates. The curvature ovalization measurement apparatus, designed by Pan et al. (1998), was used fo conducting the present curvature-controlled experiments on thin-walled tubular specimens of 304 stainless steel. It is observed that the higher the applied curvature-rate the greater is the degree of hardening of metal tube. However, the ovalization of tube cross-section increases when the applied curvature-rate increases. Furthermore due to the higher degree of the ovalization of tube cross-section for higher curvature rates under cyclic bending, the number of cycles to produce buckling is correspondingly reduced.

Viscoplastic Collapse of Thin-Walled Tubes Under Cyclic Bending

In this paper, an experimental investigation of the mechanical behavior and buckling failureof sharp-notched circular tubes subjected to cyclic bending is discussed. The unnotched and sharp-notchedcircular tubes of SUS 304 stainless steel were tested under symmetric curvature-controlled cyclic bending.It was found from moment-curvature curves that the loops show cyclic hardening and gradually steadyafter a few cycles for all tested tubes. The ovalization-curvature curves show an unsymmetric, ratchetingand increasing manner with the number of cycles. In addition, it was found that six almost parallel linescorresponding to unnotched and five different notch-depth (0.2, 0.4, 0.6, 0.8 and 1.0 mm) tubes werenoted from the experimental relationship between the cyclic controlled curvature and the number of cyclesnecessary to produce buckling on a log-log scale. An empirical formulation was proposed so that it couldbe used for simulating the aforementioned relationship. By comparing with the experimental finding, thesimulation was in good agreement with the experimental data.

Mechanical behavior and buckling failure of sharp-notched circular tubes under cyclic bending

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.

A Curvature-ovalization measurement apparatus for 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 and Lee, et al. 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.

Experimental and Theoretical Evaluations of the Effect between Diameter-to-Thickness Ratio and Curvature-Rate on the Stability of Circular Tubes under Cyclic Bending

Viscoplastic collapse of sharp-notched circular tubes under cyclic bending

This paper presents the experimental and theoretical results of the viscoplastic response and collapse of 316L stainless steel tubes subjected to cyclic bending. The tube bending machine and curvature-ovalization measurement apparatus, which was designed by Pan et al. (1998), were used for conducting the cyclic curvature-controlled experiment. Three different curvature-rates were controlled to highlight the characteristic of viscoplastic response and collapse. Next, the endochronic theory and the principle of virtual work were used to simulate the viscoplastic response of 316L stainless steel tubes under cyclic bending. In addition, a proposed theoretical formulation (Lee and Pan 2001) was used to simulate the relationship between the controlled cyclic curvature and the number of cycles to produce buckling under cyclic bending at different curvature-rates (viscoplastic collapse). It has been shown that the theoretical simulations of the response and collapse correlate well with the experimental data.

Viscoplastic response and collapse of 316L stainless steel tubes under cyclic bending

In this paper, different curvature-rates are controlled to highlight the characteristic of viscoplastic response in cyclic bending tests. The curvature-ovalization apparatus, which was designed by Pan et al. (1998), is used for conducting the curvature-controlled experiments on thin-walled tubular specimens for AISI 304 stainless steel under cyclic bending. The results reveals that the faster the curvature-rate implies, the fast degree of hardening of the metal tube. However, the ovalization of the tube cross-section increases when the curvature-rate increases.

Chien Min Hsu

Papers

A Curvature-ovalization measurement apparatus for circular tubes under cyclic bending

Experimental and Theoretical Evaluations of the Effect between Diameter-to-Thickness Ratio and Curvature-Rate on the Stability of Circular Tubes under Cyclic Bending

Viscoplastic collapse of sharp-notched circular tubes under cyclic bending

Viscoplastic response and collapse of 316L stainless steel tubes under cyclic bending

Viscoplastic analysis of thin-walled tubes under cyclic bending