Viscoplastic collapse of sharp-notched circular tubes under cyclic bending

This study discusses the experimental result of the viscoplastic response and collapse of sharp-notched 316L stainless steel tubes with different notched depths subjected to cyclic bending. The tube bending machine and curvature-ovalization measurement apparatus were used for conducting the symmetric curvature-controlled cyclic bending. To highlight the viscoplastic behavior, three different curvature-rates, 0.0035, 0.035 and 0.35 m−1s−1, were controlled. Observations of a certain curvature-rate reveal that five almost parallel lines corresponding to five different notch-depth (0.2, 0.4, 0.6, 0.8 and 1.0 mm) tubes were presented in the experimental relationship between the cyclic controlled curvature and the number of cycles needed to produce buckling on a log-log scale. However, the slopes for the three different curvature-rates are different. An empirical formulation was proposed to simulate the aforementioned relationship. When comparing with the experimental findings, the simulation was in good agreement with the experimental data.