Coarse grained molecular dynamics simulations on the uniaxial stress strain response of PMR 15

PMR-15 has a glass transition temperature of about 347 C and is widely used as a matrix material for structural composites suitable for high temperature applications. The stress strain response of PMR-15 at 316 C [1] shows that PMR-15 can sustain loads of the order of 20-30 MPa, undergo large deformations and is highly rate sensitive at temperatures even close to its glass transition temperature. In this work, we initiate the task of developing atomistically informed uniaxial constitutive models for this polymer with a view to gain insights into the interplay between mechanical properties like strain rate hardening and thermal softening with the molecular architecture and crosslinking pathways of PMR15. To this end, we start by developing reliable coarse grained (CG) models of PMR15 that can then be used in large scale Molecular Dynamics simulations to simulate its uniaxial response. The basic steps involved in the coarse graining of the bonded part of the force field follow the procedure outlined in [2]. The non bonded interactions of CG model for PMR15 is proposed to be calibrated using force matching methods similar to those employed by [3] for polystyrene. We have developed a method to enhance the validity of calibrated potentials by adding constraints for matching the virial simultaneously. This methodology will enable more accurate CG simulations to highlight the connections between key mechanical properties and the molecular details.