# Multiscale Interlaminar Enhancement of CNT Network/CF Hybrid Composites and In Situ Monitoring of Crack Propagation Behavior

## TL;DR

This paper explores how adding carbon nanotube networks to carbon fiber composites can both strengthen the material and monitor structural damage in real time.

## Contribution

The study introduces a novel multiscale interlaminar CNT network/CF hybrid composite that enables simultaneous mechanical reinforcement and in situ crack monitoring.

## Key findings

- Crack propagation in CNT/CF composites correlates with measurable changes in electrical resistance.
- Chemically modified CNT networks improve mechanical properties more effectively than thermoplastic toughening.
- The multiscale CNT/CF structure resists crack propagation in both in-plane and cross-plane directions.

## Abstract

It has long been desired to achieve mechanical enhancement and structural health monitoring by introducing carbon nanotubes (CNTs) into traditional carbon fiber (CF) composites. Herein, the initiation of micro-damage and crack propagation has been investigated by utilizing in situ electrical resistance changes in interlaminar hybrid CNT network/CF composites during the shear loading process. The results show a clear relationship between the crack propagation and the electrical resistance response particularly when approaching the failure of the single-layer CNT network hybrid composites. Furthermore, the chemically modified CNT network exhibits evident enhancement on main mechanical properties of the CF composites, superior to the thermoplastic toughening method. The characterizations manifest that the multiscale interlayered CNT/CF structure can simultaneously resist the crack propagation along both the in-plane direction and the cross-plane direction, which consequently enhances the flexural and compressive strengths of the composite material. This discovery provides a novel idea for the potential application of CNT network/CF hybrid composites in the integration of mechanical reinforcement and structural health monitoring, namely, that the CNT network acts not only as a reinforcing phase but also as a sensor for the structural health monitoring of the composites.