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

Abstract

© 2015, IFP Energies nouvelles. The work aims at identifying the key diffuso-elastic couplings which characterize a numerical tool developed to simulate the irreversible ‘Explosive Decompression Failure’ (XDF) in semi-crystalline polymer. The model proposes to predict the evolution of the gas concentration and of the stress field in the polymer during the gas desorption [DOI: 10.10161j.compositesa. 2005.05.021]. Main difficulty is to couple thermal, mechanical and diffusive effects that occur simultaneously during the gas desorption. The couplings are splitting into two families: – indirect coupling (i.e., phenomenology) that is state variables (gas concentration, temperature, and pressure) dependent; – direct coupling, (i.e., diffuso-elastic coupling) as polymer volume changes because of gas diffusion. The numerical prediction of the diffusion kinetics and of the volume strain (swelling) of PVF 2 (polyvinylidene fluoride) under CO 2 (carbon dioxide) environment is concerned. The prediction is carried out by studying selected combinations of couplings for a broad range of CO 2 pressures. The modeling relevance is evaluated by a comparison with experimental transport parameters analytically identify from solubility tests. A pertinent result of the present study is to have demonstrated the non-uniqueness of the coefficients of diffusion (D) and solubility (S g) between the diffuso-elastic coupling (direct coupling) and indirect coupling. Main conclusion is that it is necessary to consider concomitantly the two types of couplings, the indirect and the direct couplings.