In this study, a modelization of the viscoplastic behaviour of amorphous polymers is proposed, from an approach originally developed for metals behaviour at high temperature, in which state variable constitutive equat...In this study, a modelization of the viscoplastic behaviour of amorphous polymers is proposed, from an approach originally developed for metals behaviour at high temperature, in which state variable constitutive equations have been modified. The model includes the effect of strain rate sensitivity, strain softening and strain hardening. A procedure for the identification of model parameters is developed through the use of experimental data from uniaxial tests extracted from the literature, across a variety of strain rates and below the glass transition temperature ( Tg). The numerical algorithm shows that the predictions of this model well describe the intrinsic softening upon yield threshold and the subsequent progressive orientational hardening typical for amorphous glassy polymers.展开更多
The possibility to evaluate in a predictive way the relevant transport properties of low molecular weight species, both gases and vapors, in glassy polymeric membranes is inspected in detail, with particular attention...The possibility to evaluate in a predictive way the relevant transport properties of low molecular weight species, both gases and vapors, in glassy polymeric membranes is inspected in detail, with particular attention to the methods recently developed based on solid thermodynamic basis. The solubility of pure and mixed gases, diffusivity and permeability of single gases in polymer glasses are examined, considering in particular poly（2,6-dimethyl-1,4-phenylene oxide） as a relevant test case. The procedure clearly indicates what are the relevant physical properties of the polymer matrix and of the penetrants required by the calculations, which can be obtained experimentally through independent measurements. For gas and vapor solubility, the comparison with direct experimental data for mixed gases points out also the ability to account for the significant variations that solubility-selectivity experiences upon variations of pres- sure and/or feed composition. For gas and vapor perme- ability, the comparison with direct experimental data shows the possibility to account for the various different trends observed experimentally as penetrant pressure is increased, including the so-called plasticization behavior. The procedure followed for permeability calculations leads also to clear correlations between permeability and physical properties of both polymer and penetrant, based on which pure predictive calculations are reliably made.展开更多
文摘In this study, a modelization of the viscoplastic behaviour of amorphous polymers is proposed, from an approach originally developed for metals behaviour at high temperature, in which state variable constitutive equations have been modified. The model includes the effect of strain rate sensitivity, strain softening and strain hardening. A procedure for the identification of model parameters is developed through the use of experimental data from uniaxial tests extracted from the literature, across a variety of strain rates and below the glass transition temperature ( Tg). The numerical algorithm shows that the predictions of this model well describe the intrinsic softening upon yield threshold and the subsequent progressive orientational hardening typical for amorphous glassy polymers.
文摘The possibility to evaluate in a predictive way the relevant transport properties of low molecular weight species, both gases and vapors, in glassy polymeric membranes is inspected in detail, with particular attention to the methods recently developed based on solid thermodynamic basis. The solubility of pure and mixed gases, diffusivity and permeability of single gases in polymer glasses are examined, considering in particular poly（2,6-dimethyl-1,4-phenylene oxide） as a relevant test case. The procedure clearly indicates what are the relevant physical properties of the polymer matrix and of the penetrants required by the calculations, which can be obtained experimentally through independent measurements. For gas and vapor solubility, the comparison with direct experimental data for mixed gases points out also the ability to account for the significant variations that solubility-selectivity experiences upon variations of pres- sure and/or feed composition. For gas and vapor perme- ability, the comparison with direct experimental data shows the possibility to account for the various different trends observed experimentally as penetrant pressure is increased, including the so-called plasticization behavior. The procedure followed for permeability calculations leads also to clear correlations between permeability and physical properties of both polymer and penetrant, based on which pure predictive calculations are reliably made.
