Numerical and Experimental Determination of Strains in the Vicinity of a Centrally Located Circular Discontinuity in AA6061-T6 Square Extrusions during Axial Crushing

An experimental and numerical investigation was conducted on AA6061-T6 extrusions with centrally located through-hole discontinuities to investigate the strains in the vicinity of the crush trigger. The extrusions used in this research were of square cross sectional geometry with a nominal side width of 38.1 mm, wall thickness of 3.15 mm and length of 200 mm. Centrally located circular discontinuities with a diameter of 14.29 mm were incorporated into the extrusion through CNC machining. The axial crushing tests were performed in a quasi-static manner using a hydraulic Tinius-Olsen tension/compression testing machine and observed using a GOM Aramis optical strain measuring device focusing on the region in the vicinity of the discontinuity. A finite element model previously developed by Arnold and Altenhof was selected to compare strains in the region of the through-hole. The material definition for the AA6061-T6 extrusion utilized in this FE model incorporated damage mechanics theory which was able to accurately predict material failure after a two-stage calibration process. All simulations considered in this research were completed using LS-DYNA® version 970 revision 5434a. Good predictive capabilities of the strain magnitudes and distributions were observed from the numerical simulations. In the vicinity of the discontinuity, at the stress concentration region and at maximum crushing force, the effective strain was observed to range from 4.5% to 15.5% in LS-DYNA simulations. Experimental observations on the effective strain ranged from 5.0% to 15.7%. This information is important in the understanding of large deformation behaviour for AA6061-T6 extrusions, which could be applied in structural crashworthiness applications.