The ductility requirements of strut-based metamaterials

Additive manufacturing of refractory metals provides a pathway for the pro-duction of architected lattice structures for high-temperature applications inaerospace and reactor technologies. However, these materials are often brittle,and the additive manufacturing process introduces defects that generate sub-stantial variability in local material properties, making lattice performancedifficult to predict. To quantify the interplay between limited material duc-tility and defect sensitivity, a high-throughput computational framework isdeveloped. Individual strut properties—strength and ductility—are sampledfrom Weibull distributions, and Monte Carlo simulations are used to relatethese input distributions to the effective lattice response. A transition in failuremechanism is identified. At low material ductility, the lattice strength isgoverned by strut rupture, whereas at higher ductility, widespread yieldingproduces plastic collapse that defines the upper bound on the lattice strength.Below this ductility threshold, the rate at which lattice strength increaseswith ductility strongly depends on the degree of defect scatter; above it,further increases in ductility provide only marginal benefit. The influenceof geometric stress concentrations is further examined using notched spec-imens. Two material populations that exhibit nearly identical strengths underuniform tension display markedly different notch sensitivities: the high-ductility material approaches notch-insensitive behavior, whereas the low-ductility material exhibits a strength knockdown well beyond the net-sectionprediction. These results underscore the importance of notch-sensitivitystudies in the evaluation of new alloys and additive manufacturing processesfor lattice-based components.