Mechanical and temporal response of high-coordinated irregular network reinforced composites

Irregular architected materials offer a wide design space of mechanical properties beyond that of typical periodic architected materials. However, these irregular materials are often completely stochastic, offering little control over the structure-to-property relationships. Here, we show that intentional design of irregular materials, using topology and geometry, leads to control of the mechanical response. We demonstrate this experimentally using additively manufactured two-phase polymer composites, which we generate using a hexagonal virtual growth algorithm (hexa-VGA). The hexa-VGA tessellates a finite set of hexagonal tiles into an irregular network according to coordination number, defined as the average number of connections per network node. In contrast to prior work on the topic of network reinforced composites, the hexa-VGA allows the design of reinforcing architectures characterized by a broader design space, having a coordination number that spans from one to six, representing a purely monodisperse and regular network. The designs generated by the hexa-VGA are then additively manufactured into two-phase materials, with the network being made of a stiff reinforcing phase, while the space enclosed by the network is filled with a soft elastomeric matrix. Through plate tension tests, we show the dependence between the coordination number and the mechanical properties of the polymer composites, and we highlight design pathways to control temporal variations in the fracture response and improve damage tolerance.