A two-phase model for the diffuso-mechanical behaviour of semicrystalline polymers in gaseous environment

Abstract

a b s t r a c tThe increasing use of semicrystalline polymers (SCPs) in complex petroleum structures which are subjected to high variations of temperature and gas pressure requires the development of reliable and predictive constitutive models. For that purpose a diffuso-elastoviscoplastic model is presented here by considering a two-phase representation, classically used in porous media, for the representative volume element (RVE) of SCP in gaseous environment. One phase is crystalline (skeleton), and the other corresponds to the mixture (fluid) of gas and free amorphous (the latter is considered penetrable by gas). The modelling is described within the framework of the thermodynamics of irreversible processes with internal variables. General balance equations are established by considering the above RVE. The general diffuso-mechanical macroscopic continuum formulation obtained is applied to elastoviscoplastic behaviour. The implementation of this two-phase diffuso-elastoviscoplastic model in Abaqus TM software via a user subroutine allows to study the interactions between crystal, free amorphous and gas during a rapid decompression test. More precisely, the evolution of pressure in the two-phase polyvinylidene fluoride SCP is given during a decompression test with carbon dioxide. Some results are discussed. The presented model is supposed to facilitate the introduction of damage criterion in order to describe the blistering occurring during a decompression.

Diffuso-Kinetics and Diffuso-Mechanics of Carbon Dioxide / Polyvinylidene Fluoride System under Explosive Gas Decompression: Identification of Key Diffuso-Elastic Couplings by Numerical and Experimental Confrontation

“…To date, a body of models tentatively describes the existence of strong couplings between mechanical, thermal and diffusive phenomena occurring in polymeric materials in fluid transport, with the additional difficulty in modeling the state of the fluid within the polymer. Theoretical descriptions of these coupling phenomena are based on empirical or thermodynamic interpretations, as given in the selected open literature [25][26][27][28][29][30][31][32][33][34][35][36][37].…”

“…These laws have been implemented into the engineering finite element code Abaqus TM by means of an User ELement (UEL) subroutine, as applied in [32][33][34][35][36][37]. To simulate the couplings, it is used 9 000 finite elements defined in the UEL with 20 nodes and 27 integration points.…”

“…To simulate the couplings, it is used 9 000 finite elements defined in the UEL with 20 nodes and 27 integration points. Details can be found in [35][36][37].…”

Thermodynamics and Thermokinetics to Model Phase Transitions of Polymers over Extended Temperature and Pressure Ranges Under Various Hydrostatic Fluids

“…Transported fluids contain important amounts of dissolved species, which on operating temperature and pressure may influence the resistance of the engineering structures depending on the thermodynamic T, P-conditions and various phenomena as sorption/diffusion, chemical interactions (reactive fluids, i.e., oxidation), mechanical (confinement) changes. The polymer damage occurs when rupture of the thermodynamic equilibrium (i.e., after a sharp pressure drop) activates the blistering phenomenon, usually termed as 'explosive decompression failure' (XDF) process (Dewimille et al, 1993;Rambert et al, 2006;Baudet et al, 2009). Damage is a direct result of specific interactions between semi-crystalline patterns and solvent with a preferential interaction (but not exclusive) in the amorphous phase Devisme et al, 2007).…”

“…Approaches addressing the prediction of the multifaceted thermo-diffuso-chemomechanical (TDCM) behaviour are being suggested. Constitutive equations are built within a thermomechanical framework, like the relation based on a rigorous thermodynamic approach , and the proposed formalism based on as well rigorous mechanical approach (Rambert et al, 2006;Baudet et al, 2009). …”