Crashworthiness and Material Characterization of Multi-cellular AA6063 Extrusions

Abstract

This thesis investigates the crashworthiness characteristics of the AA6063-T6 aluminum extrusions with two different multi-cellular cross-sections. The profiles under study are referred to as the Omega cross-section which is used in a commercially produced automobile and the UWR4 cross-section developed by Kohar et al. (Kohar C. Internationla Journal of Impact Engineering, vol 95, 2016) to improve the energy absorption properties of the axial rails. The aluminum profiles were crushed in the axial direction in dynamic and quasi-static crush modes. Peak loads, average crush loads, energy absorption and specific energy absorption of the different cross sections are then compared. Based on these comparisons, the UWR4 cross-section was found to display superior energy absorption properties compared to the Omega profile. Overall, the UWR4 profile developed by Kohar et al. improved the specific energy absorption of the rails (compared to the Omega cross-section) by 35.8% and 43.2% in dynamic and quasi-static axial crush experiments, respectively. The aluminum alloy used in this work was studied for strain rate sensitivity through uniaxial tensile experiments in different strain rate regimes (10-3 s-1 – 103 s-1). These experiments are performed using miniature dog bone tensile samples developed to study strain rate sensitivity on various tensile frames. Simple shear experiments were also performed to better understand the hardening behaviour of the aluminum alloy. The results of these experiments were then used to model the constitutive behaviour of the alloy using a generalized Voce constitutive model. The anisotropy of the aluminum alloy was characterized through tensile tests performed in the extrusion, diagonal and transverse directions. These experiments revealed the presence of a strong directional dependence of the mechanical properties of the alloy. The geometrical constraints of the rails made it impractical to utilize biaxial tension tests; instead, through-thickness compression tests were used to characterize the biaxial tension region of the yield surface. These results were then used to calibrate the YLD2000-2d anisotropic yield surface. The results of the yield surface fit showed a good agreement with the experimental values. The results of the yield surface calibration along with the constitutive equation were used to model the dynamic and quasi-static axial crush experiments of the respective aluminum rails. The results of the numerical models predicted the average loads of the aluminum rails within 10% of the experimental values. Some improvement in the predictions should be possible through the use of brick elements rather than the current shell elements.