Mechanics of three-dimensional micro-architected interpenetrating phase composites

Composite materials are used across engineering applications for their superior mechanical performance, a result of efficient load transfer between the structure and matrix phases. However, the inherently two-dimensional structure of laminated composites reduces their robustness to shear and out-of-plane loads, while unpredictable interlaminar failure and fiber pull-out can cause a catastrophic loss of load capacity. Meanwhile, advances toward uncovering structure-property relations in architected materials have led to highly tunable mechanical properties, deformation, and even failure. Some of these architected materials have reached near-theoretical limits; however, the majority of current work focuses on describing the response of a single-material network in air, and the effect of adding a load-bearing second phase to a three-dimensional architecture is not well understood. Here, we develop facile fabrication methods for realizing centimeter-scale polymer- and carbon-based architected interpenetrating phase composite (IPC) materials, i.e., two-phase materials consisting of a continuous 3D architecture surrounded by a load-bearing matrix across length scales, and determine the effect of geometry and constituent material properties on the mechanics of these architected IPCs. Using these experiments together with computational models, we show that the matrix phase distributes stress effectively, resulting in a high-strength, stable response. Notably, failure delocalization enhances energy dissipation of the composite, achieving specific energy absorption (SEA) values comparable to those of wound fiber tubes. Finally, we demonstrate that the stress state in an IPC can be tuned using geometric design and introduce an example in an architected composite. Altogether, this work bridges the gap between mechanically efficient composites and tunable architected materials.