Dégradation chimique du PE et influence sur le comportement, l'endommagement et la rupture en fluage : application à la durabilité des canalisations sous pression

Abstract : High density polyethylene pipes (HDPE) appear to be more and more significant in drinking water distribution networks. A good microbiological quality of the distributed water is ensured by adding disinfectants, such as chlorine. The durability of these pipes, initially designed for a 50 years lifetime, is a great challenge for Veolia, which requires a realistic renewal plan. For this purpose, two approaches have been developed: the first one predicts the physico-chemical state of PE after changes due to the contact with chlorine, while the second one estimates the residual lifetime of a pipe, containing cracks initiated by aging. The kinetic scheme of chemical degradation results from the thermooxidation of PE, to which radical initiating reactions due to chlorine were added. Kinetic rates and diffusion coefficients are determined from the experimental results obtained on accelerated aged samples. The influence of oxidation on PE mechanical response under creep loading is then studied from two grades of PE, representatives of two degradation states: the initial material and an aged one. Damage and failure mechanisms are determined according to the degree of aging. The mechanical approach aims at assessing the creep crack growth of a defect initiated after the oxidation process at the inner surface in contact with disinfectants. Two methodologies are suggested to estimate the residual lifetime of a pipe: the global approach, which relies on a master curve C* = f(tR); and the local approach which takes the damage mechanisms into account to model the failure by using finite element analysis. This latter requires constitutive equations, which are based on the experimental results obtained at both macroscopic and microscopic scales.
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Clémence Devilliers. Dégradation chimique du PE et influence sur le comportement, l'endommagement et la rupture en fluage : application à la durabilité des canalisations sous pression. Matériaux. École Nationale Supérieure des Mines de Paris, 2011. Français. ⟨NNT : 2011ENMP0094⟩. ⟨pastel-00711486⟩

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