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Structural Engineering and Mechanics
  Volume 28, Number 5, March30 2008, pages 495-514
DOI: http://dx.doi.org/10.12989/sem.2008.28.5.495
 


Mean moment effect on circular thin-walled tubes under cyclic bending
Kao-Hua Chang, Wen-Fung Pan and Kuo-Long Lee

 
Abstract
    In this paper, experimental and theoretical investigations of the effect of the mean moment on the response and collapse of circular thin-walled tubes subjected to cyclic bending are discussed. To highlight the influence of the mean moment effect, three different moment ratios r (minimum moment/ maximum moment) of -1, -0.5 and 0, respectively, were experimentally investigated. It has been found that the moment-curvature loop gradually shrinks with the number of cycles, and becomes stable after a few cycles for symmetric cyclic bending (r = -1). However, the moment-curvature loop exhibits ratcheting and increases with the number of cycles for unsymmetric cyclic bending (r = -0.5 or 0). In addition, although the three groups of tested specimens had three different moment ratios, when plotted in a log-log scale, three parallel straight lines describe the relationship between the controlled moment range and the number of cycles necessary to produce buckling. Finally, the endochronic theory combined with the principle of virtual work was used to simulate the relationship among the moment, curvature and ovalization of thin-walled tubes under cyclic bending. An empirical formulation was proposed for simulating the relationship between the moment range and the number of cycles necessary to produce buckling for thin-walled tubes subjected to cyclic bending with different moment ratios. The results of the experimental investigation and the simulation are in good agreement with each other.
 
Key Words
    moment-controlled; mean moment; moment ratio; thin-walled tube; cyclic bending; ovalization; collapse; endochronic theory.
 
Address
Kao-Hua Chang and Wen-Fung Pan: Dept. of Engineering Science, National Cheng Kung University, Tainan, Taiwan 701, R.O.C.
Kuo-Long Lee: Dept. of Computer Application Engineering, Far East College, Tainan County, Taiwan 744, R.O.C.
 

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