Comportement mécanique de fibres et d'assemblages de fibres en polyester pour câbles d'amarrage de plates-formes offshore

Faced with the need to exploit off-shore oil fields at ever increasing depths, lighter replacements are being considered for the standard steel cable mooring systems used for platforms. This study considers the mechanical behaviour of synthetic ropes made of two different materials: PET and PEN. The first is already used in ropes to replace steel, and the second could be a potential competitor. A multi-scale study, involving mechanical tests (mainly tensile, creep and cyclic loading) has been carried out on assemblies of various sizes, from ropes of several hundreds kN breaking load to their smallest components: filaments. Strong correlations were found between the quasi-static behaviour of assemblies and the behaviour of filaments, which in itself is determined by mechanisms at the molecular level. This has shown that the effects of the geometry of the assemblies are limited and can easily be identified. However, results from cyclic loading tests have shown that the consideration of all the mechanisms that could cause failure at the single filament level (creep, tensile fatigue, hysteresis heating...) is not sufficient to explain the failure of ropes. This implies the contribution of other mechanisms associated with fibre assemblies, such as abrasion. The comparison of results from tests on both materials showed that PEN, of which very little is known, exhibits a mechanical behaviour very similar to that of PET.