Vol. 9, No. 2, 2014

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Dynamic compression of square tube cellular structures

Ryan L. Holloman, Karthikeyan Kandan, Vikram Deshpande and Haydn N. G. Wadley

Vol. 9 (2014), No. 2, 149–182
Abstract

Aluminum cellular structures have been fabricated by combining a two-dimensional [${0}^{\circ }$/$9{0}^{\circ }$]${}_{2}$ arrangement of square Al 6061-T6 alloy tubes with orthogonal tubes inserted in the out-of-plane direction. By varying the tube wall thickness, the resulting three-dimensional cellular structures had relative densities between 11 and 43%. The dynamic compressive response of the three-dimensional cellular structure, and the two-dimensional [${0}^{\circ }$/$9{0}^{\circ }$]${}_{2}$ array and out-of-plane tubes from which they were constructed, have been investigated using a combination of instrumented Kolsky bar impact experiments, high-speed video imaging, and finite element analysis. We find the compression rate has no effect upon the strength for compression strain rates up to 2000 s${}^{-1}$, despite a transition to higher-order buckling modes at high strain rates. The study confirms that a synergistic interaction between the colinear aligned and out-of-plane tubes, observed during quasistatic loading, extends to the dynamic regime. Finite element simulations, using a rate-dependent, piecewise linear strain hardening model with a von Mises yield surface and an equivalent plastic strain failure criterion, successfully predicted the buckling response of the structures, and confirmed the absence of strain-rate hardening in the three-dimensional cellular structure. The simulations also reveal that the ratio of the impact to back-face stress increased with strain rate and relative density, a result with significant implications for shock-load mitigation applications of these structures.

Keywords
cellular structures, 6061 aluminum, impact testing, dynamic loads, material rate-dependence