EFFECTS OF STRAIN RATE, TRANSVERSE PRESSURE AND FIBER SURFACE ROUGHNESS ON TRACTION LAWS OF GLASS FIBER EPOXY INTERPHASES

Abstract

In this study, molecular dynamic simulations (MD) are used to study the effects of strain rate, and transverse pressure (i.e. residual stress and impact loading) on the traction separation response of a glass fiber epoxy interphase where the fiber has nanoscale surface roughness. The interphase model is prepared with and without monolayer glycidoxypropyltrimethoxy silane (GPS). The glass fiber surface roughness profile is created from a surface map measured experimentally using atomic force microscopy (AFM). To develop the atomistic interphase model, first we deposit GPS molecules (in case of interphase with silane) on the silica (fiber) surface and react them with the silica surface through a condensation reaction. A mixture of Epon828-Jeffamine® D-230 is then placed on the silica surface and equilibrated using the general AMBER force field. The interphase structure is finally created through the epoxide-amine curing reaction among the epoxy, silane and amine using a cross-linking algorithm. The model is then subjected to Mode-I and Mode-II loading with the reactive force field ReaxFF to predict the interphase traction-separation responses and failure loci within the interphase. To investigate the effects of strain rate and transverse pressure (in case of Mode-II), interphase loading is carried out at 109/s to 1011/s strain rates and 1 atm to 4 GPa pressure that is applied normal to the fiber surface. Simulation results suggest that the Mode-II interphase traction-separation response improves with the increase in strain rate and transverse pressure. Strain-rate and pressure dependent MD traction data can be used to bridge length scales as input into micromechanics and meso-scale models.