Influence of redundant hole on the degradation and failure of round-hole tubes under cyclic bending

This article introduces the effect of redundant holes (RDHs) on the performance of 6061-T6 aluminum alloy round-hole tubes (Al-RHTs) subjected to cyclic bending. In this study, Al-RHTs with a fixed hole diameter of 2, 4, 6, 8 or 10 mm were drilled to acquire an RDH of the same size on the same cross section but at different positions: 45°, 90°, 135° and 180°. The moment–curvature relationship demonstrated a steady loop from the first cycle. The RDH at any position showed a slight influence on the relationship. However, the ovalization–curvature curve displayed ratcheting, increasing, asymmetrical, and bowtie-like trends as the number of cycles increased. The RDH position shows substantial influence on the relationship. Although the Al-RHTs were tested with five different hole diameters and different RDH positions, the curvature-number of cycles needed to initiate failure relationships in a log–log scale displayed parallel straight lines for each hole diameter. Finally, an empirical formulation proposed by Lee, Weng, and Pan in 2019 was modified and improved to simulate the above relationships. The simulation result was compared with the experimental results, and it was found that the theoretical analysis could reasonably reproduce the experimental results.