Studies on the failure of synthetic alpinistic ropes

Alpinistic ropes, usually made in polyamide 6 (PA,6) are characterized by a very complex architecture, from elemental component (fibre or yarn) to the next higher structures (strand). There are on the market ropes showing strands twisted or braided together in different ways, so the resultant properties depend on the material the ropes are made with and on the hierachical structure of the rope. In operation, ropes have to support strong loadings, in particular for the climber’s safety is relevant the resistance to subsequent loading (Dodero test) and the ability of taut ropes not to break against sharp corners of falling rocks (Sharp corner test). These phenomena have been simulated in laboratory. Experimental results shows that the apparent elastic modulus and stress/strenght curves are strictly in relationship with the type of envelopment. In particular melting of the polymer occurs along the rope even far from the breaking point, due to the friction of the yarns sliding back after the rupture. X rays demonstrate that a fast recystallization occurs in the molten zones. Braided ropes show better perfomance in sharp corner test due to a slower speed of the yarns sliding back, whereas twisted ropes behaves better in resistance to subsequent loadings.