Session: 03-05-01: Nanomaterials

Paper Number: 107118

107118 - A Novel Atomistic-Continuum Concurrent Coupling Method for Simulating Fracture in Polymers 

There exists a wide range of problems where localized phenomena in certain regions of the domain are of interest, such as the stress concentration at the tip of a macro-scale crack. To be able to study these local phenomena using a high accuracy multi-sale model, while globally retaining a more efficient, lower accuracy model, has been the subject of research over the past few decades. Research in concurrent coupling seek to partition the domain so that multiple models can operate simultaneously, as opposed to the hierarchical approach. The key to achieving this lies in the interface between the domains and how information is transmitted between their respective models.

In the present work, we seek to address problems involving bridging of length-scales in the mechanics of materials and structures. Specifically, our target is to better model nanoscale behavior in the vicinity of cracks, voids, and nanoparticles in amorphous materials. These nanoscale behaviors can be uncovered using Molecular Dynamics (MD) models within a localized region. Outside of the zone of interest, we may use a continuum model such as the Finite Element Method (FEM). Thus, we have a particle representation of the material in a localized region of interest and a continuum representation elsewhere.

Many of the techniques developed so far for concurrently coupling particle and continuum domains are specific to crystalline materials. The work by Pfaller et al. are among the first to involve an amorphous polymer in coarse-grained particle representation. In the so called Arlequin technique used by Pfaller, the anchor points are randomly dispersed in the bridging domain and coupled to the monomer particles in a thermoplastic matrix. In the present study, however, we are interested in studying a cross-linked thermosetting polymer in all-atom representation. We propose an enhancement to Pfaller’s method in which the bridging domain is subdivided into Interface Volume Cells (IVC), and the anchor points are connected to groups of atoms instead of individual atoms. The coupling spring forces are distributed over the groups of atoms, potentially avoiding any localized stress concentrations.  

Thus, a new simulation technique, based on the Arlequin framework and the Anchor Point method, is presented for concurrently coupling atomistic and continuum domains at finite temperatures with focus on all-atom molecular representations of thermosetting polymers. Next, the method is applied to simulate uniaxial tensile tests on a bar of thermosetting polymer (EPON-862) with crosslinking agent DETDA. For the polymer, the first case studied is uniaxial tension at temperature of 1 K in order to reduce thermal oscillation of atoms. Finally, a concurrently coupled simulation of Mode I crack growth in a thermoset polymer is presented and the atomistic J-integral computed to predict the fracture toughness of epoxy.

 

Presenting Author: Sankha Subhra Aditya University of Alabama

Presenting Author Biography: Sankha Aditya graduated from Indian Institute of Technology (IIT), Kharagpur in India with a B.S. and M.S. degree in Aerospace Engineering. He is currently pursuing his PhD in the Aerospace Engineering Department at the University of Alabama with Dr. Samit Roy as his PhD adviser.

Authors:

Sankha Subhra Aditya University of Alabama
Samit Roy University of Alabama