Fracture Characterization of Bioinspired Irregular Network Reinforced Composites

TL;DR

This study investigates the fracture behavior of bioinspired irregular network reinforced composites, revealing how network structure and material properties influence energy dissipation and crack propagation, with implications for designing tailored fracture responses.

Contribution

It introduces a new approach to characterize fracture in irregular NRCs, highlighting the roles of network coordination and structural features in energy dissipation mechanisms.

Findings

Low coordination NRCs dissipate energy mainly through plastic zones.

High coordination NRCs dissipate energy mainly through crack extension.

Two critical length scales govern fracture response: plastic zone size and structural feature geometry.

Abstract

The mechanical behavior of composite materials is significantly influenced by their structure and constituent materials. One emerging class of composite materials is irregular network reinforced composites (NRC's), whose reinforcing phase is generated by a stochastic algorithm. Although design of the reinforcing phase network offers tailorable control over both the global mechanical properties, like stiffness and strength, and the local properties, like fracture nucleation and propagation, the fracture properties of irregular NRC's has not yet been fully characterized. This is because both the irregular reinforcing structure and choice of matrix phase material significantly affect the fracture response, often resulting in diffuse damage, associated with multiple crack nucleation locations. Here, we propose irregular polymer NRC's whose matrix phase has a similar stiffness but half the strength of the reinforcing phase, which allows the structure of the reinforcing phase to control the fracture response, while still forming and maintaining a primary crack. Across a range of network coordination numbers, we obtain J-integral and R-curve measurements, and we determine that low coordination polymer NRC's primarily dissipate fracture energy through plastic zone formation, while high coordination polymer NRC's primarily dissipate energy through crack extension. Finally, we determine that there are two critical length scales to characterize and tailor the fracture response of the composites across the coordination numbers: (i) the size of the plastic zone, and (ii) the size and geometry of the structural features, defined as the areas enclosed by the reinforcing network.