Piezoresistive Monitoring of Carbon Nanomaterial-Reinforced Epoxy Composites Under Cyclic and Fatigue Loading: A Review

Abstract

The use of carbon nanomaterials as piezoresistive reinforcements in epoxy composites offers a promising route for smart structures capable of real-time structural health monitoring (SHM). These nanocomposites exploit the exceptional electrical and mechanical properties of carbon nanotubes and graphene nanoplatelets to enable strain-sensitive responses within insulating polymer matrices. Despite their potential, challenges remain for reliable long-term sensing. This review examines the piezoresistive performance of carbon nanotube- and graphene-reinforced epoxy systems under cyclic and fatigue loading. Sensitivity, often quantified by gauge factors exceeding conventional strain gauges, depends on optimized filler contents near the percolation threshold and electron tunneling conduction. Piezoresistive responses can capture damage evolution via measurable resistance changes during fatigue. However, limitations persist: effects of hysteresis, recovery, synergistic nanofiller interactions, and environmental durability are underexplored, and few studies address performance beyond 104 cycles or under multiaxial loading. Challenges in nanoparticle dispersion, network stability, and the lack of standardized sensing protocols hinder reproducibility and scalability. Future advancements will require hierarchical nanofiller architectures, multimodal sensing integration, and rigorous testing methods. Overcoming these obstacles is crucial to transform piezoresistive nanocomposites from experimental concepts into robust, scalable SHM solutions for next-generation composite structures.