Atomistic prediction of plane stress behavior of glassy thermosets

Abstract

When any covalent bond energy reached a threshold indicative of incipient bond scission, the simulation was stopped. This method was used to examine the responses of three highly-crosslinked epoxy systems. Systems were large enough to include 110 to 480 crosslink sites. Both elastic and yield properties show good agreement with the experiments of others. Continuum yield theories commonly applied to polymers are compared with the data. A Drucker-Prager pressure-dependent yield function applied best in the second and third quadrants of the σ1σ2 domain. In the first quadrant, however, data more closely match a normal-stress-yielding criterion. In biaxial tension and simple tension, plastic behavior and large growth in nano-porosity were observed. Ductility was lowest in simple tension and biaxial compression. In simple tension, the bonds at crosslink sites and in ether linkages were the most highly strained whereas carbon-carbon backbone bonds between phenyl groups were highly strained in other cases. When system energy at imminent bond rupture was divided on a per-atom basis, consistency with Peterlin’s theory for molecular rupture was found.