Dynamic Compression of Square Tube Cellular Structures

Aluminum cellular structures have been fabricated by combining a two-dimensional [0◦/90◦]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◦/90◦]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.