Micro level damage monitoring techniques in functionalized natural fiber composites based on electrical conductivity -A review on adaptation and challenges towards non-structural applications

• Scope of functionalized natural fiber composites in non-structural applications. • Micro level damage monitoring techniques in functionalized natural fiber composites. • Adoptability of electrical conductivity based damage monitoring techniques in functionalized natural fiber composites. • Challenges in electrical conductivity based damage monitoring. Functionalized natural fiber composites (FNFCs) are developed by encompassing conductive fillers (CF) / conductive polymers (CP) at nanoscale level. The unique properties of natural fibers (NFs) make FNFCs as sustainable alternatives for synthetic materials specifically in non-structural applications. However, FNFCs tend to undergo micro level damages due to mechanical loading and environmental factors. The real-time monitoring of damages at the micro level by using non-destructive testing (NDT) and structural health monitoring (SHM) techniques becomes crucial which makes it difficult to ensure the structural integrity and reliability of FNFCs. Past literatures focused only on conductive synthetic fiber materials, so it is tough task to adapt same techniques on NFs composite materials. The present review critically analyzes and reports the adaptability of electrical resistance change (ERC) and electrical impedance tomography (EIT) techniques for efficiently monitoring the micro level damages in FNFCs. The present study explores the relationship between damage induced resistivity changes and NFs properties, fiber-matrix interface behavior, conductive pathways, and the influence of environmental factors. Also addresses key challenges including variability in fiber distribution, matrix incompatibility, and the reproducibility of conductivity measurements. Bridging knowledge gaps, present work outlines a framework for integrating electrical conductivity based damage monitoring into FNFCs. This approach promotes their applications in non-structural domains such as flexible sensors, smart textiles and energy storage.