Microscopic deformation and failure modes of high-functionality epoxy resins from bond breaking molecular dynamics simulations and experimental investigation

The material behavior of the API-60 epoxy resin was investigated using atomistic molecular dynamics simulations. In this study, a hybrid, reactive force field (M-GAFF2), which combined Morse and harmonic bond potentials from GAFF2, was developed to understand the elastic/plastic response of the cured epoxy polymer. We found that elastic deformation was caused by epoxy network rearrangement at low strain while plastic deformation was observed by stretching and breaking covalent bonds after the yield point. Ab initio calculations at the CASPT2(2,2)/6-311+G* level of theory were performed to compute parameters for M-GAFF2. These are necessary for breaking covalent bonds in the epoxy network backbone when they are deformed. The M-GAFF2 was effective in revealing the ductile-like deformation behavior of the crosslinked epoxy polymer at the microscopic level, including elastic/plastic deformations and progressive failure. The effect of testing temperature at 300 and 400 K and degree of cure (DoC) on tensile properties such as Young's modulus, ultimate strength, and failure strain was evaluated to verify the feasibility of the M-GAFF2 in different thermodynamic constraints. This new approach is easy to use for nonequilibrium MD simulations and computationally efficient for studying the microscopic deformation and failure behavior of thermosetting polymers at the atomistic scale.

Automated summary

The material behavior of API-60 epoxy resin was investigated using atomistic molecular dynamics simulations. A hybrid, reactive force field (M-GAFF2) was developed to understand its elastic/plastic response. The study revealed that elastic deformation was caused by epoxy network rearrangement, while plastic deformation occurred after the yield point by stretching and breaking covalent bonds. M-GAFF2 effectively revealed the ductile-like deformation and failure behavior of the epoxy polymer at the microscopic level. The feasibility of M-GAFF2 under different thermodynamic constraints was verified by evaluating the tensile properties at different temperatures and degree of cure.