EFFECT OF CRACK LENGTH ON FRACTURE TOUGHNESS IN EPOXY POLYMERS USING ATOMISTIC-CONTINUUM COUPLING OF MD WITH FEM

Abstract

Developing fundamental methodologies for predicting material properties, such as strength and toughness, is one of the core objectives of Integrated Computational Materials Engineering (ICME). For this purpose, a generalized framework for anchor point based concurrent coupling of FEM and MD domains, encompassing previous related methods, is presented in this paper. The motivation for this work comes from the fact that the crack length and fracture process zone size required to simulate brittle fracture in certain materials, such as epoxy polymers, often exceed the computational size limit needed for pure MD simulation. The proposed concurrent coupling framework is robust and is agnostic of material crystallinity and atomistic description. Two distinct forms of the method are discussed in detail, both of which are able to make use of specialized MD solvers such as LAMMPS with little or no modification. One of the two forms has the added advantage of being able to couple to specialized FEM solvers as well, such as ABAQUS. The two methods are tested against each other in a uniaxial tension test using a graphene monolayer at 300 K temperature and a block of thermosetting polymer EPON862 at 1 K temperature, showing comparable results. Convergence behavior of the two coupling methods are studied. The methods are then applied to study the fracture of a center-cracked graphene monolayer and compared with results from an identical pure MD simulation, using the atomistic Jintegral. Their good agreement corroborates the effectiveness of the developed method and potential use as a plug-and-play tool to couple commercial FEM and MD solvers. Future work will entail applying these methods to simulate elevated-temperature amorphous polymer models and their brittle fracture, and the effect of crack length and process zone size.