![]() deflection response depicted in Figure 1B. The second being where the post-buckling stiffness may be relatively low, idealized in the mechanical load vs. The first phase being the pre-buckling (fundamental) behavior, where the stiffness is relatively high and the required load-carrying capacity is established. Therefore, low structural stiffness needs to be combined with a high load-carrying capacity this is an area where post-buckling behavior of structural components may be exploited since structures that undergo instabilities tend to have at least two mechanical phases under compressive loading. This would render the soft material to be practically unsuitable in terms of the necessary thickness of material to facilitate the deformation required to absorb the energy efficiently. deflection response graph depicted in Figure 1A, demonstrates that the required structural displacements, characterized by δ 0 in the graph, providing the desired energy absorbency could be excessively large. Although a very soft (intrinsically low stiffness) material with a relatively high yield stress would technically be able to perform this task, the load vs. This is because low stiffness leads to diminished stress propagation and has been shown to be effective in isolating sacrificial structures from a more important one ( Virgin and Davis, 2003). ![]() For such sacrificial structures to be practically effective, they need to have certain properties: primarily, a low structural stiffness is necessary ( Schenk and Guest, 2014). Critically important structures, which require protection from, for instance, impact or blast, can be shielded by attaching protective sacrificial structures that absorb the energy of the hazardous load while imparting stresses that are insufficient to cause damage to the more important structure. Instabilities may be readily exploited in applications involving energy absorption or structural isolation. In the design of metamaterials, the nonlinear behavior of their internal structure can result in some rather unexpected but potentially exploitable features ( Bertoldi et al., 2017)-this is especially the case for auxetic materials that are designed to have a negative Poisson's ratio ( Masters and Evans, 1996 Bertoldi et al., 2009 Grima et al., 2009 Körner and Liebold-Ribeiro, 2015 Hunt and Dodwell, 2019). More recently, in the fields of mechanical and aeronautical structures, instabilities have been used in so-called smart shape-morphing materials and structures that switch from one geometric form to another under particular loading ranges ( Arena et al., 2018) this also has significance in the field of energy harvesting ( Hu and Burgueño, 2015). Of course, in the field of thin-walled structures, the naturally stable post-buckling of plates has been exploited since the 1940s due to the pioneering work of, amongst others, von Kármán et al. However, with the rapid emergence of nonlinear mathematics, computational power, alongside numerical, and manufacturing techniques, the exploitation of the geometrically nonlinear range is becoming increasingly feasible for a wider range of applications ( Reis, 2015 Champneys et al., 2019). The conventional wisdom in terms of the perception of structural instabilities has been that they are best avoided in practice. The concept may be extended to promote cellular buckling where the internal lattice buckles with densification occurring at defined locations and in sequence to absorb energy while maintaining a low underlying mechanical stiffness. It is demonstrated that such disruptions can be arranged to enhance the panel performance. The desirable properties of a high fundamental stiffness and a practically zero underlying stiffness in the post-buckling range ensure that energy may be absorbed within a limited displacement and that any transfer of strain to an attached structure is minimized as far as is feasible. ![]() Currently, the internal structure of the lattice core is deliberately disrupted geometrically to engineer suitable post-buckling behavior under quasi-static loading. Advances in additive manufacturing increasingly allow bespoke, carefully designed, structures to be included within the core lattice to enhance mechanical performance. ![]() The energy absorption and structural isolation performance of axially-compressed sandwich structures constructed with stiff face plates separated with an auxetic lattice core metamaterial is studied.
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