Internal contact and damage in aramid fibre ropes
Oday Allan is a PhD student in the department Surface Technology and Tribology. (Co) Promotors are prof.dr.ir. M.B. de Rooij and dr. T. Mishra from the Faculty Engineering Technology (ET), University of Twente.
High-performance synthetic fibre ropes are increasingly used in offshore, lifting, and safety-critical applications such as lightweight replacements for steel wire ropes. Among these, three-strand ropes made from para-aramid fibres (e.g. Twaron®) combine high tensile strength with flexibility. However, their complex internal architecture makes them susceptible to degradation at strand–strand interfaces, which are hard to assess with existing rope monitoring techniques. Because this damage develops internally and is difficult to detect, rope lifetimes are still managed through conservative replacement rules, leading either to safety risks or premature disposal. This industrial challenge motivates the main aim of the thesis: to develop quantitative methods for characterising the degradation and the relevant contact mechanics at the internal strand interfaces of three-strand aramid ropes.
This research addresses the challenge through a combined, multi-scale experimental and analytical approach. At the strand scale, pressure-sensitive films were used to measure inter-strand contact pressures and contact widths, while digital image correlation captured changes in rope geometry under load. At the filament scale, X-ray micro-computed tomography (µCT) enabled segmentation of thousands of individual filaments, providing direct measurements of filament orientation and packing fraction, which were used to compute relative slip at the strand interfaces. These experimental insights were then implemented to develop semi-analytical models describing rope geometry, strand retraction, and contact mechanics at the strand interfaces. A refined double-helix model was developed that accounts for strand flattening, enabling calculation of local contact forces, contact widths, and slip distributions.
Building on this contact-mechanical foundation at the strand interfaces, the thesis further investigates degradation in three-strand ropes. Fourier-transform infrared (FTIR) spectroscopy was applied to detect molecular-level damage in Twaron® fibres, with specific spectral markers identified and normalised to reference peaks. By correlating these signatures with scanned images of fibrillation and damaged filaments, FTIR provides a non-destructive indication of internal rope damage. Finally, an energy-based damage indicator is introduced based on the contact models developed for strand interfaces. The damage indicator combines modelled contact pressure and slip at the strand interfaces into a scalar measure of frictional energy dissipated per load cycle. This indicator provides a link between internal mechanics and observed degradation, laying the groundwork for predictive lifetime models specifically for three-strand ropes. While the present framework is tailored to this construction, the methods provide a basis for future extension to other rope architectures.
In summary, the thesis contributes to: (i) new experimental methods for assessing strand- and filament-scale mechanics in three-strand Twaron® ropes, (ii) a refined analytical framework for rope geometry and interface contacts, (iii) a non-destructive FTIR-based method for assessing interfacial fibre damage, and (iv) an energy-based indicator connecting contact pressure and slip to degradation. Together, these advances improve the scientific understanding of the mechanical behaviour at the rope’s internal interfaces and provide practical tools for lifetime prediction and condition-based monitoring of synthetic fibre ropes in demanding applications.
