Experimental observations on the crush characteristics of AA6061 T4 and T6 structural square tubes with and without circular discontinuities

Abstract

Abstract Quasi-static compressive testing of extruded aluminum alloy 6061-T4 and 6061-T6 square cross-sectional tubular specimens, with and without the presence of dual centrally located circular hole discontinuities, was completed to investigate the load management and energy absorption characteristics of these structural members. The tubular geometries selected (tube lengths of 200 mm and 300 mm, wall thickness of 3.15 mm, and nominal side width of 38.1 mm) had parameters which result in predicted global bending collapse under compressive loading. Centrally located circular holes, machined into the two opposing walls of the tubes, were used as crush initiators to commence the plastic buckling process. Holes with diameters of 7.1 mm and 14.2 mm were considered. In addition to progressive buckling, collapse modes involving cracking and splitting were observed in many tests and are characterized using photographs of the experimental process. The collapse modes and energy absorption of the crush test specimens were found to be dependent largely on material properties and to a lesser extent on the diameter of the discontinuity. Significant increases in the crush force efficiency, up to a maximum of approximately 22%, were observed for the shorter length tube geometry. However, the presence of the circular discontinuity within the AA6061 T4 300 mm tubes slightly degraded the crush force efficiency compared to the same length tubular member without any discontinuity. Energy absorption capabilities were substantially improved for all AA6061- T6 specimens containing a circular discontinuity relative to the specimens without any crush initiators. With the addition of the discontinuity, energy absorption was improved for the 200 mm length AA6061-T4 specimens but slightly decreased for the 300 mm length members.