Numerical simulation study on plastic buckling of thin-walled aluminum alloy tubing under cyclic bending

Abstract

The 6061-T6 thin-walled tube material is prone to cyclic plastic buckling failure during rotational straightening and reciprocating bending service. In actual rotational straightening production lines and long-term reciprocating bending service, the tube bears repeated alternating positive/negative bending curvature loads with a single-cycle maximum bending angle of ±3.2° and loading frequency of 0.2 Hz, which is defined as the cyclic bending load condition investigated in this work. The initial wrinkling geometric defect significantly deteriorates its stable load-bearing performance. Taking the 6061-T6 thin-walled tube with an outer diameter of 12 mm and a wall thickness of 0.5 mm as the research object, a 1/2 symmetric three-dimensional finite element model considering geometric large deformation, material nonlinearity and Bauschinger effect was established based on ABAQUS; the multi-linear follower strengthening constitutive description was adopted to describe the cyclic plastic behavior, and the cumulative incremental plasticity method was proposed to solve the multi-cycle bending loading. The influence of the laws of two wrinkling defect introduction methods, namely eigenvalue superposition and direct modeling, on the buckling evolution was compared. The results show that the material hardening and Bauschinger effect jointly cause stiffness degradation, and the critical instability curvature of the tube decreases exponentially with the number of cycles; for the thin-walled tube with a diameter-to-thickness ratio of 24, the branch-type buckling is dominant, and a 0.01 t mid-span wrinkling defect will significantly reduce the ultimate load-bearing capacity; compared with eigenvalue superposition defects, the direct modeling introducing axial + circumferential global wrinkling is more in line with engineering manufacturing deviations and has a higher degree of buckling failure. The cyclic buckling numerical analysis method established in this study can provide theoretical support for the straightening process of aluminum alloy thin-walled tubes and the design of anti-stable structures.