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 highlycrosslinked 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 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 nanoporosity 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.

Hierarchical Multiscale Approach for Modeling the Deformation and Failure of Epoxy-Based Polymer Matrix Composites

“…Thus, in the current simulations, if any bond along the DGEBA monomer (i.e., C-A super-atoms) reaches this bond-breaking threshold, the bond is treated as a broken bond. It should be noted that considering bond breaking only along the DGEBA monomer is in agreement with QM/MM simulations that show that the bonds between benzylic carbon and the phenyl group in the DGEBA are the most frequently broken bonds and not the bonds involving the nitrogen atom at the cross-linking site. , …”

“…It should be noted that considering bond breaking only along the DGEBA monomer is in agreement with QM/MM simulations that show that the bonds between benzylic carbon and the phenyl group in the DGEBA are the most frequently broken bonds and not the bonds involving the nitrogen atom at the cross-linking site. 21,22 The bond length checking is not performed every time step in the simulations but rather at a prescribed frequency. This is due to the significant computational cost associated with this check in a large simulation.…”

On the Nature of Epoxy Resin Post-Curing

“…The effects of each processing step, resin chain length, and the sign of the stress in uniaxial loading (i.e., tension versus compression) are illustrated in Figures 13 and 14. The method for loading the samples is described in [52]. A plane stress state (e.g., biaxial tension) and strain rate is selected.…”

“…This was accomplished by applying a succession of dynamics simulations. Stress values were kept in the proportion to match the chosen stress state and adjusted to maintain constant strain rate [52].…”