Deformation Of Glassy Polymers Research Articles

Micromechanical characterization of composite materials based on poly(styryl pyridine) thermoset resin

AbstractThe purpose of this paper is to propose a micromechanical characterization of composite materials through measurement of the work‐hardening rate K in the preyield stage during compression tests at constant strain‐rate. This method belongs to a more general framework where the non‐elastic deformation of glassy polymers is analyzed from a metallurgical point of view. The parameter K varies as the inverse of the nucleation rate of dislocations which are responsible for the non‐elastic deformation. The method is used, here, to characterize a model composite material : PSP resin (poly(styryl pyridine)) filled with glass beads. K measurements show that introducing glass beads in the PSP resin enhances its ability to deform plastically, i.e. the presence of glass beads increases strongly the nucleation rate of dislocations. K‐measurements and scanning electron microscopy investigations seem to show that the coupling agent A1100 is not appropriate to the PSP matrix.

Detailed Modeling of Structure and Deformation of Glassy Polymers

The molecular structure of macromolecules determines to a very large extent the macroscopic properties of the polymers they make up, and delimits what variations in properties can potentially be effected by processing. It is, therefore, important to understand and to be able to reliably predict the relevant properties of polymers and the limits of these properties upon treatment from the knowledge of the molecular structure of the constituent chains. For many properties of amorphous polymeric glasses correlations have been introduced in the last decades; some of them have been very useful [1–3], but they lack basic understanding of the processes and mechanisms operative in the generation of the properties in question. Their application is, by definition, limited to interpolation in that part of “chemical structure space” used as basis for the correlation. Prediction implies the power of extrapolation and, consequently, some use of first-principle methods. Remarkably little such work [1, 4–6] has been done to date on amorphous polymeric glasses. We have recently begun to investigate the atomistic-level modeling of structure and properties of amorphous, “fully relaxed” polymeric glasses [7–9].

Plastic flow in glassy polymers

AbstractMassachusetts Institute of Technology Cambridge, Massachusetts 02.139 The phenomenology of plastic deformation in glassy polymers is described, and a theory based on a molecular model for such deformation is presented and contrasted with other published theories. A phenomenological yield criterion is presented which is consistent with the theory. It is shown that the theory is in very good accord with experimental results on the temperature dependence of the plastic shear resistance of a large group of glassy polymers with widely different molecular structures. Finally, the formation and growth of shear deformation bands is described, based purely on the mechanics of localization processes in inelastically deforming continua.

Interpretation of shift of relaxation time with deformation in glassy polymers in terms of excess enthalpy

The mechanical relaxation time in a glassy polymer depends on the magnitude of strain. The stress relaxation modulus of a styrene acrylonitrile and polybutadiene composite system (ABS) was measured at strains ranging from 0.005 to 0.10. The relaxation time was observed to shorten by up to four orders of magnitude. In addition, there was observed a decrease in the elastic contribution to the modulus. These two aspects of nonlinear viscoelasticity are interpreted in terms of the excess enthalpy associated with dilatation under strain, a crucial factor for ductile behavior and the formation of crazes. Up to 0.9 cal/g of the excess enthalpy associated with the stress-induced dilatation is obtained from the differential scanning calorimetry study.