The effect of fiber orientation on the electrical resistance change behavior of glass fiber reinforced polymer composites

Fibre-reinforced polymers are widely used in the aerospace and automotive industries due to their high specific strength and corrosion resistance. It is necessary to perform in situ monitoring of these composites to ensure their structural integrity under service conditions. In this context, electrical resistance change (ERC) is a promising method for detecting damage in real time. This study investigates the influence of glass fibre orientation (0°, 15°, 30°, 45°, 60°, 75°, and 90°) on ERC behaviour in unidirectional glass fibre/epoxy composites modified with 0.3 wt.% multiwalled carbon nanotubes. The composites were manufactured via vacuum bagging and subjected to quasi-static three-point bending and uniaxial tension while monitoring electrical resistance continuously. The results showed that the loading mode strongly affects both damage mechanisms and ERC behaviour. Under tensile loading, the maximum ERC exceeds 30%, whereas bending leads to only a 4% change. Increasing the fibre orientation angle significantly reduces ERC sensitivity: when subjected to bending, the ERC decreases from ~3%-4% to less than 1%, while under tension, the ERC decreases from ~25%-30% to nearly 5%. These findings demonstrate the critical role of fibre orientation in interpreting the ERC-based structural health monitoring signals.