Compressive response of multilayered pyramidal lattices during underwater shock loading

The quasi-static and dynamic compressive mechanical response of a multilayered pyramidal lattice structure constructed from stainless-steel was investigated. The lattices were fabricated by folding perforated 304 stainless steel sheets and bonding them to thin intervening sheets using a transient liquid-phase bonding technique. The resulting structure was attached to thick face sheets and the through thickness mechanical response was investigated quasi-statically and dynamically, in the latter case using a planar explosive loading technique. The lattice is found to crush in a progressive manner by the sequential (cooperative) buckling of truss layers. This results in a quasi-static stress strain response that exhibits a significant “metal foam” like stress plateau to strains of about 60% before rapid hardening due to truss impingement with the intermediate face sheets. During dynamic loading, sequential buckling of the truss layers was manifested as a series of transmitted pressure pulses measured at the back face of the test samples. The sequential buckling extended the duration of the back face pressure–time waveform and significantly reduced the transmitted pressure measured at the back face. The impulse transmitted to the structure is found to be about 28% less than that predicted by analytic treatments of the fluid-structure interaction for fully supported structures. This transmitted impulse reduction appears to be a consequence of the wet side face sheet movement away from the blast wave and is facilitated by the low crush resistance of the lattice structure.