局部凹痕圓管之循環彎曲退化與失效

In this paper, we present an experiment and an analysis method for inspecting the deterioration and failure of locally-dented 6061-T6 aluminum alloy tubes under cyclic bending. A simple technique was employed to produce small transverse local dents on the tubes. Tubes with dent depths varying from very shallow to approximately 2.4 times the tube wall thickness were considered. The ovalization-curvature curve showed an increase in asymmetry and ratcheting with an increase in the number of bending cycles. Deeper dent depths caused larger ovalization. Tubes with five different dent depths were tested. The relationship between the controlled curvature and number of bending cycles required to produce failure on a log-log scale exhibited five nonparallel straight lines. Finally, a finite element model was used to describe the moment-curvature and ovalization- curvature relationship. In addition, an empirical formula was suggested to simulate the relationship between the controlled curvature and number of bending cycles required to produce failure. It was found that the experimental and analytical data agreed well.