Extraction of Thermal Properties of Organic Ablative Materials Using Molecular Dynamics Simulations

Abstract

In this study, molecular dynamics method is used for extracting thermal properties of materials relevant to the ablative type of thermal protection system. The methodology and results are discussed for extracting thermal conductivity and specific heat capacity of ablative materials for their virgin and char states in a manner that is defined in the experimental data sets. To select a suitable nonreactive force field, Green-Kubo simulations are performed over phenol, toluene, and benzene materials using Amber, Dreiding, and all-atom optimized potentials for liquid simulations (OPLSAA) force fields. Next, crosslinked and non-crosslinked polymers are created, and pyrolysis simulations are performed over them using ReaxFF to obtain virgin and char states of the polymers. Thermal conductivity is extracted using the Green-Kubo method, whereas specific heat capacity is extracted by using the enthalpy gradient obtained by performing isobaric simulations over virgin and char materials. Later, by introducing the concept of an artificial composite material, the extracted thermal properties are used in macroscale one-dimensional heat conduction simulations with pyrolysis using an in-house finite element method (FEM)-based thermal response solver.