A damage model for the blistering of polyvinylidene fluoride subjected to carbon dioxide decompression

Semicrystalline polymers (SCPs) used in complex petroleum structures are subjected to high variations of temperature and gas pressure, which induce some damage. For this reason, the Representative Volume Element (RVE) of a SCP evolving in a gaseous environment is modelled using a phenomenological approach based on the porous media theory. SCPs are in fact two-phase materials at the scale of the spherolite. One phase is crystalline (skeleton), and the other corresponds to a mixture (fluid) of gas and free amorphous medium (the latter is considered penetrable by gas). The modelling is described within the framework of the thermodynamics of irreversible processes with internal variables by considering the above RVE. An elastoviscoplastic model with cavity growth is proposed within the framework of general diffuso-mechanical continuum media. The aim is to predict the evolution of ductile damage observed during decompression. This two-phase diffuso-elastoviscoplastic-damage model is implemented in Abaqus® software via a user subroutine. This numerical tool allows us to study the damage of polyvinylidene fluoride SCP during a rapid decompression test.The influence of the decompression rate on the evolution of initial cavities is discussed. Comparison with experiments shows the relevance of the proposed model as far as blistering is concerned. We hope that the present model can help understanding the occurrence of damage mechanisms during decompression.