Brittle Slow Crack Growth in Polyamide 11: Mechanics and Mechanisms (Creep and Ageing)

摘要

In the oil industry, polymers are used for sheathing dynamic risers. Polymer sheaths keep the flexible waterproof and allow for the steel spirals displacements. The polymer has to be ductile at the working temperature (up to 90°C), and this justifies the use of polyamides and fluorinated polymers. Because they are exposed to a high temperature in a fluid environment, the polymers progressively age. In the present study, we examine the evolution of mechanical properties of PA 11 between two states: as received and aged. Using precracked DENT specimens, we achieved to reproduce the brittle slow crack growth which seems to be observed in field aged PA 11. Moreover, an appropriate numerical model is established. The computations are in good agreement with the experimental results. The model is intended to help design of sheaths, and thus to prevent failures.