Control of load/displacement responses of AA6061-T6 and T4 circular extrusions under axial compressive loads

摘要

Axial crushing of AA6061-T6 and T4 circular extrusions with variable wall thicknesses was completed under both dynamic and quasi-static loading conditions to investigate the capability of controlling the load/displacement responses of the extrusions. Circular specimens with a nominal original wall thickness of 3.175 mm, an outer diameter of 50.8 mm, and a length of 300 mm were considered. Variations of the wall thickness in the axial direction were completed by material removal from the extrusion sidewall prior to crushing tests. Cutters used in this research had a height of 20 mm and blade tip widths of 1.0 mm. A curved deflector was used to flare the cut petalled sidewalls and facilitate the cutting system. Results from the impact tests illustrated that an initial peak cutting force with a magnitude of 1.08-1.74 times higher than that for the quasi-static loading was needed to initiate the cutting deformation mode. After this transient cutting stage, the load/displacement responses were observed to be similar to that from the quasi-static tests except for some slight fluctuations resulting from a minor amount of material fracture which occurred on the petalled sidewalls. A lesser extend of material fracture was observed on the T4 temper specimens due to the work hardening material property of the T4 temper condition. The mean cutting force from the dynamic tests were determined to be in the range of 0.92-1.09 times the mean force from the corresponding quasi-static test. Control of load versus displacement responses of the extrusions under both impact and quasi-static compressive loading conditions was accomplished through the variation of the wall thickness along the axial direction of extrusions.