carbon nanolattices: optimized lattices + ultra strong constituents

Carbon micro/nano lattices are a unique family of architected metamaterials constructed from micro/nano-scale carbon constituents [1]. During the past few years, they have demonstrated exciting potentials in reaching theoretical limits of mechanical performances as well as integrating properties which are often mutually exclusive through experimental studies and numerical simulations [2-8]. The combination of small-scale carbon constituents and unlimited architecture designs of lattice opens a broad exploration space for better material properties in carbon nanolattices.

Besides strength, ductility matters.

Besides pursuing high specific strength, ductility is also particularly important to carbon nanolattices for robust performances [7].

• At the material level, the carbon constituents, most made of graphene, are strong but intrinsically brittle [14]. To make use of the ultrahigh strength of graphene, it is also important to enhance the toughness and ductility.
• At the structure level, buckling is an important mechanism to dissipate energy in nanolattice materials under compression [16-18]. However, permanent and continuous damage often accompanies buckling events. Under tensile loading, buckling can have much limited effect on energy dissipation [4, 5].

Given the great potentials of carbon nanomaterials, it is important to enrich the design library of carbon nanolattices with examples of novel energy dissipation mechanisms in order to overcome this challenge.

Snap-through instability: marco and micro scales

Like buckling, snap-through instability has been a long-time research topic [22-29]. Recent studies unveil some unique advantages of this instability.

• On one hand, at macro-scale, sequential snap-through instabilities can be triggered under compressive and tensile loading conditions [25, 28] with little irriversibkle damage [28]. Metamaterials with snap-through instability often exhibit multiple mechanically stable states, which open doors to the design of shape-reconfigurable materials (SRMs) [25].
• On the other hand, at small scales, basic conceptual units with mechanically bi-stable states and snap-through instability [30-33] have been adopted to explain deformation behaviors of phase transforming materials, including structure proteins with compactly folded or unfolded domains [34, 35] and shape memory alloys undergoing martensitic phase transformation [36].

Such universal structure-to-property relationship indicates great potential in engineering complex overall deformation behavior via bi-stable units and snap-through instabilities.