Concurrently coupled multiscale modeling of polymer nanocomposites

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University of Alabama Libraries

Embedded statistical coupling method (ESCM) was originally developed to provide computational efficiency, to decrease coupling complexities, and to avoid the need to discretize the continuum model to atomic scale resolution in concurrent multiscale modeling. ESCM scheme is relatively easy to implement within conventional FEM code and has been tested in standard solid lattice structures. However, this method encounters difficulties when being implemented for amorphous materials like polymers, due to the fact that they lack specific ordered lattice structure and atoms may not be covalently bonded with each other, which are the requirements of common coupling schemes. Therefore, a new approach needs to be developed to resolve this problem. In this paper, details of a modified ESCM approach for atomistic-continuum coupling developed to perform simulations of crack growth in polymers is presented. The presence of the continuum domain surrounding the MD region allows for the application of far-field loading, and prevents stress wave reflections from the external boundary impinging back on the crack tip. In our approach, Material Point Method (MPM), which is a meshless particle-in-cell method based on Arbitrary Euler-Lagrange (ALE) scheme and has been proven to have good performance in large deformation problems, is used to model the continuum domain. It is concurrently coupled with molecular dynamics (MD), a widely used method in atomistic simulations, using a so-called handshake region. Anchor points, the equilibrium positions of the constrained particles, which are designed to transmit displacements and forces between nanoscale and macroscale model, are defined in the handshake region. A concurrently coupled MPM-MD simulation of crack propagation inside a polymer is performed to verify this new coupling approach, thereby providing a better understanding of the fracture mechanisms at the nanoscale to predict the macro-scale fracture toughness of polymer system. Results are presented for concurrently coupled crack propagation simulation in a di-functional cross-linked thermoset polymer, EPON 862. The composite laminate open hole tension problem is also studied using concurrent multiscale approach by implementing micromechanics program MAC/GMC in FEA frame.

Electronic Thesis or Dissertation
Aerospace engineering, Mechanics, Mechanical engineering