MODELLING FRICTION IN THE YARN-ON-YARN ABRASION TEST
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Summary
Resistance of rope-making fibers to self-abrasion can be an important factor determining the service life of ropes subjected to long-term cycling, e.g. in tension-tension fatigue or in cyclic bending over sheave (CBOS) service. The standard ASTM D6611 / Cordage Institute CI1503 Yarn-on-Yarn test is well-established for comparing the abrasion resistance of various industrial fibers for rope industry service. Previous theoretical treatments of this method have generally assumed a simple helical geometry during testing, however this representation of the test would only be appropriate in the absence of friction/abrasion and so is inconsistent with the actual test conditions. Friction drives the commonly observed shifting of the yarn-on-yarn contact region during testing which can significantly influence abrasion rate and thereby cycles-to-failure test results. The model presented here builds upon a vector-based parametric model introduced previously, with an improved treatment of frictional forces and better representation of the interaction of external force vectors. Although model solutions are possible for sheave and bollard examples, a general solution to the yarn-on-yarn test geometry was not found. A similar parametric method is also used to recommend twist levels in the test (or similar friction coefficient tests) based on consideration of filament-level yarn interactions.
Author: F. Sloan
