A Screen-Printed Carbon Nanotube/Epoxy Array for Impact Monitoring in Construction Safety Helmets

Conventional construction safety helmets provide passive protection but do not record impact occurrence or location. Recording this information could support post-impact inspection, motivating the integration of distributed sensing onto the curved helmet shell. This study develops a screen-printed carbon nanotube (CNT)/epoxy sensor array for multichannel impact monitoring. Rheological and electrical characterization guided sensor fabrication, while impact tests examined how CNT loading and sensing-disc geometry affected response magnitude and variability. A 5.0 wt.% CNT formulation with a 10 mm sensing disc was selected and integrated onto the inner shell as a 19-channel array. Channel-specific resistor-substitution calibration enabled resistance-based response analysis. Three independently fabricated arrays detected all 240 crown impacts at nominal energies of 0.2-4.0 J. Across 90 impacts at three off-crown positions, the median angular deviation was 6.2°. These findings demonstrate an approach to extending helmet functionality through low-energy impact detection and regional localization using printed CNT/epoxy sensors.