Architectured materials comprised of periodic arrangements of nodes and struts are 11 lightweight materials that can exhibit combinations of properties which are inaccessible to 12 conventional solids. However, with regards to their mechanical performance, they have an 13Achilles heel in that these materials can exhibit a catastrophic post-yielding collapse, causing 14 substantial drops in strength and energy absorption during plastic deformation. This post-15 yielding collapse is the result of the activity of single shear bands, and originates from the single 16 orientation of macro-lattices. We observe that this behaviour is analogous to deformation by slip 17 in metallic single crystals. In this study we propose that, by mimicking the microstructure 18 observed in crystalline materials, we may be able to employ hardening mechanisms found in 19 crystalline materials to help us to develop robust and damage-tolerant architected materials. This 20 study demonstrates that crystal-inspired meso-structures can play as an important role in the 21 mechanical properties of architectured materials as do crystallographic microstructures in the 22 case of metallic alloys. Consequently, designing meso-structures that mimic crystallographic 23 microstructure in crystalline metals enables the fusion of metallurgy and architectured materials 24 to transform the way of designing a new type of materials with desired properties. 25 26 Main text references 363

Crystal-inspired approach is found to be highly successful in designing extraordinarily damage-tolerant architected materials. i.e. meta-crystals, necessitating in-depth fundamental studies to reveal the underlying mechanisms responsible for the strengthening in meta-crystals. Such understanding will enable greater confidence to control not only strength, but also spatial local deformation. In this study, the mechanisms underlying shear band activities were investigated and discussed to provide a solid basis for predicting and controlling the local deformation behaviour in meta-crystals. The boundary strengthening in polycrystal-like meta-crystals was found to relate to the interaction between shear bands and polygrain-like boundaries. More importantly, the boundary type and coherency were found to be influential as they govern the transmission of shear bands across meta-grains boundaries. The obtained insights in this study provide crucial knowledge in developing high strength architected materials with great capacity in controlling and programming the mechanical strength and damage path.

No abstract

Architected lattice metamaterials offer extraordinary specific strength and stiffness that can be tailored through the architecture. Meta-crystals mimic crystalline strengthening features in crystalline alloys to obtain high strength and improved post-yield stability of lattice materials. This study investigates synergistic effects of the base material’s intrinsic crystalline microstructure and architected polycrystal-like architecture on the mechanical behavior of architected metamaterials. Four different polygrain-like meta-crystals were fabricated from 316L, Inconel 718 (IN718) and Ti6Al4V via laser powder bed fusion (L-PBF). While the elastic modulus of the meta-crystals did not vary significantly with the base material or the number of meta-grains, the strength of the meta-crystals showed strong increasing correlation with reducing the size of meta-grains. The differences between meta-crystals made by the three alloys were the most substantial in the post-yield behavior, where the 316L meta-crystals were the most stable while Ti6Al4V meta-crystals were the most erratic. The differences in the post-yield behavior were attributed to the base material’s ductility and intrinsic work-hardening. For all base materials, increasing the number of meta-grains improved the post-yield stability of meta-crystals. The tolerance to the processing defects also differed with the base material. Detrimental defects such as the high surface roughness on the downskin of the struts or the large, irregularly shaped pores near the surface of the struts led to early strut fracture in Ti6Al4V meta-crystals. In contrast, ductile IN718 was able to tolerate such defects, enabling the most significant synergistic strengthening across lengthscales to achieve architected materials of low relative density, but with a very high strength and an excellent energy absorption.

No abstract