a b s t r a c tCompressible cellular metal sandwich structures made from a 3D assembly of square cross section 6061 T6 aluminum alloy tubes, and face sheets of the same alloy have been attached to a vertical pendulum and impacted by synthetic wet sand with an incident velocity of~300 ms À1 . The transmitted impulse of samples with thick (relatively rigid) and thin face sheets are compared to that transferred by an incompressible solid aluminum test block of the same dimensions. A discrete particle-based simulation method was used to simulate the experiments and to investigate the soil particle e structure interaction with the cellular structures. The simulated results agreed very well with experimental data; both showed that the impulse transferred to cellular structures with a 22 MPa core strength was 10e15% less than that transferred to a solid block of similar dimensions. However, the simulations reveal that the some of this apparent mitigation resulted from a subtle sand interaction between the bottom of the test structure and the sand box used for the tests. When this sand box effect was eliminated in the simulations, a small impulse reduction from cellular structures with thin face sheets was still observed. However, this was found to be a result of dynamic deflection of the edges of the front face sheet. When this effect was eliminated (by the use of a rigid front face), the simulations showed a small (5%) impulse reduction occurred for cellular structure whose compressive strength was much less than the pressure applied by the sand. This was a consequence of rapid core compression which increased the travel distance (and lateral spreading) of late arriving sand during the sand loading process. Weak cellular structures, that suffered significant crushing, also reduce the impulse transfer rate.
We explore a novel cellular topology structure based upon assemblies of square cross section tubes oriented in a cross-ply 2D and orthogonal 3D arrangements that can be tailored to support different combinations of through thickness and in-plane loads. A simple dip brazing approach is used to fabricate these structures from assemblies of extruded 6061-T6 aluminum alloy tubes and the through thickness compression of a variety of structures is investigated experimentally and with finite element modeling. We find that the 3D orthogonal structures have an approximately linear dependence of modulus upon relative density. However the strength has a power law dependence upon density with an exponent of approximately 5/3. These cellular structures exhibit almost ideal plastic energy absorption at pressures that can be selected by adjustment of the vertical and in-plane tube wall thicknesses. A finite element model with a nonlinear hardening constitutive law is used to explore the buckling modes of the structure, and to investigate the relationship between cell topology, relative density, tube wall material properties and the cellular structures resistance to compression.
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. Plane waves at the boundary of two micropolar thermoelastic solids with distinct conductive and thermodynamic temperatures RAJNEESH KUMAR, MANDEEP KAUR and SATISH C. RAJVANSHI 121 Dynamic compression of square tube cellular structures RYAN L. HOLLOMAN, KARTHIKEYAN KANDAN, VIKRAM DESHPANDE and HAYDN N. G. WADLEY 149 Dynamic response of twin lined shells due to incident seismic waves J. P. DWIVEDI, V. P. SINGH and RADHA KRISHNA LAL 183 Solutions of the von Kármán plate equations by a Galerkin method, without inverting the tangent stiffness matrix HONGHUA DAI, XIAOKUI YUE and SATYA N. ATLURI 195 Bimaterial lattices with anisotropic thermal expansion MARINA M. TOROPOVA and CRAIG A. STEEVES 227 Origin and effect of nonlocality in a composite STEWART A. SILLING 245
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