A High‐Performance and Sensitive Strain Sensor Based on MWCNT /Epoxy for Micro‐Strain Monitoring of Steel Structure

Accurate micro‐strain monitoring is vital for civil engineering structural integrity, yet conventional sensors, like metal strain gauges, face limitations in sensitivity and conductivity. Flexible nanocomposite sensors, though advanced for wearable electronics and healthcare, primarily detect strains > 0.1%. To address this limitation, a novel multi‐walled carbon nanotube (MWCNT)/epoxy composite strain sensor was developed through a facile screen‐printing technique. Systematic optimization of MWCNT morphology, percolation thresholds, and curing protocols enabled exceptional sensitivity in micro‐strain detection. The optimized sensor demonstrates exceptional electromechanical performance, achieving a high gauge factor (GF) of 7.32 with excellent linearity ( R 2 = 0.99) over a broad strain range of 0–20,000 με, and an even higher GF of 34 with outstanding linearity ( R 2 = 0.98) within the micro‐strain range of 0–100 με. The sensor also exhibits high electrical conductivity (82.56 S/m) and a stable percolation threshold of 3.4 wt.%. Furthermore, the sensor maintains consistent performance over 10,000 cycles under strain amplitudes ranging from 0.5% to 1.6%, demonstrating remarkable cycling stability and durability. In tensile tests on steel sheets, the sensor accurately captured strain variations, closely aligning with measurements from metal strain gauges and testing machines. Additionally, the sensor successfully underwent a 200‐day in situ monitoring of reinforced concrete supports in a metro pit, highlighting its potential for long‐term structural health monitoring in civil engineering applications. This work advances the field of strain sensing by providing a high‐performance, durable, and cost‐effective solution for micro‐strain detection in civil infrastructure.