Microscopic deformation and failure modes of high-functionality epoxy resins from bond breaking molecular dynamics simulations and experimental investigation
CW Jang and JW Mullinax and JH Kang and FL Palmieri and TB Hudson and JW Lawson, POLYMER ENGINEERING AND SCIENCE, 62, 3952-3963 (2022).
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.
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