Assessing internal mechanical damage in aramid ropes using ATR-FTIR spectroscopy

We present a novel approach to use Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) spectroscopy for assessing internal damage in Twaron® aramid ropes subjected to cyclic bending fatigue loading at various stages of the fatigue life. After testing, rope specimens were analysed under two configurations: (1) an “open-strand” configuration, where an individual strand was untwisted and isolated from a double-twisted three-strand rope to enable direct ATR measurement of the heavily damaged filaments, and (2) a “closed-rope” configuration, where measurements were conducted at the observable strand–strand interface, sampling a broader transverse region consisting of both highly and less-damaged filaments. The main aim of studying these two configurations was to evaluate ATR-FTIR as a non-destructive technique for internal damage characterisation in industrial aramid ropes. The effect of fibre orientation on FTIR spectra was examined to isolate it from the effect of mechanical damage on the spectra. FTIR spectral analysis involved normalising absorbance spectra to an internal reference band and tracking changes in peak intensity at 1110 cm -1 as a damage indicator. In open-strand measurements, the 1110 cm -1 absorbance showed a sharp initial decline before stabilising at higher damage levels. In contrast, closed-rope measurements exhibited a more gradual reduction, reflecting the averaging effect of mixed damage states across the measured region. A bounded exponential fit of the absorbance–damage relationship showed a strong correlation with damage progression, confirming that FTIR-derived peak absorbance ratios serve as reliable indicators of internal degradation. Moreover, changes in rope size (3- vs. 6-yarn strands) showed a minimal effect on spectral trends, supporting the scalability of the method to larger industrial ropes. Additional imaging using electron microscopy and computed tomography (CT) scanning revealed progressive fibrillation and peeling, localised at outer regions of the strand–strand interface, validating the non-invasive damage characterisation approach using a closed-rope configuration. This non-destructive spectroscopic technique offers a practical tool for monitoring internal fibre damage in high-performance aramid ropes, enabling improved preventive maintenance and more accurate service life predictions. • ATR-FTIR spectroscopy effectively tracks fatigue-induced damage progression in Twaron® ropes. • FTIR absorbance ratio (A 1110 / A 1514 ) correlates with internal damage progression. • Method enables rapid, non-invasive damage assessment across various rope sizes and constructions. • SEM and micro-CT imaging validate surface fibrillation and interfacial wear mechanisms.