Session: 03-10-02: Micromechanics and Multiscale Modeling

Paper Number: 161672

161672 - Predicting Fracture Toughness in Polymers Using Multi-Scale Atomistic-Continuum Concurrent Coupling 

Prediction of fracture properties in quasi-brittle materials using computer simulations is the primary objective of this paper. One of the main challenges to achieving this goal for brittle thermoset polymers is that the crack size and fracture process zone (FPZ) size needs to be in the micron scale in order for linear elastic fracture mechanics (LEFM) to be valid, thereby enabling toughness prediction and comparison with macro-scale experimental data.  However, due to the high computational cost of performing purely atomistic simulations with millions of atoams, the range of crack lengths and FPZs simulated have been severely limited to nanometer scale,  resulting in highly incorrect toughness estimates. In this paper, a state-of-the-art multiscale modeling technique is employed to allow atomistic simulations to run with much larger crack lengths and process zone sizes to truly replicate conditions necessary for brittle fracture in a polymer. A thermosetting epoxy polymer system of EPON862/DETDA is modelled using the  OPLS molecular dynamics (MD) force field available in LAMMPS, coupled with Morse potential which allows for bond breakage. The MD system is concurrently coupled with a much larger finite element model (FEM) using the Capriccio algorittm.

The atomistic-continuum coupling is performed using a novel anchor-point based statistical method incorporating internal volume cells (IVCs), with displacement and strain continuity enforced in the handshake region using Lagrange multipliers. Atomistic J-integral , developed by the authors, is used to compute the fracture energy near the crack tip using contour integrals. The critical strain energy release rate (SERR) is computed using the atomistic J-integral specifically developed by the authors for simulating fracture in amorphous polymers. The applied mode 1 stress intensity factor (K₁ ) is increased and its effect on the size of FPZ and critical SERR is studied. The in-house FEM code is integrated into concurrent coupling code, which iteratively executes the coupled MD simulations.  Our preliminary results indicate a monotonic increase in notch-sensitivity and FPZ with the increasing size of a subcritical crack, with the predicted SERR from atomistic J-integral tending towards macro-scale G_C for epoxy as the FPZ becomes fully developed.  The toughness enhancing effect of dispersed graphene nanoplatelets in the polymer near the crack-tip is also evaluated using the coupled appraoch.  

Presenting Author: Samit Roy University of Alabama

Presenting Author Biography: Dr. Samit Roy received his Ph.D. in Engineering Science & Mechanics from Virginia Tech in Blacksburg, Virginia. He is currently the William D. Jordan Endowed Professor in the Department of Aerospace Engineering and Mechanics at University of Alabama (UA). Dr. Roy's research interest is directed towards multi-scale modeling and life-prediction of fiber reinforced polymer composites and structural adhesives subjected to aggressive environmental conditions. He is also actively involved in the application of nanostructured reinforcements in enhancing performance of composite materials. He has developed structural health management concepts that include sensor placement optimization for structural weight and cost reduction, as well as smart materials for non-autonomous self-healing. He has authored over 200 peer-reviewed journal articles and book chapters. He was elected Associate Fellow of the American Institute of Aeronautics and Astronautics (AIAA) in 2004, elected Fellow of ASME in 2010, and Fellow of American Society for Composites (ASC) in 2022. He was elected Chairman of the ASME NanoEngineering for Energy and Sustainability (NEES) steering committee in 2014, and Division Chair, Emerging Composite Technologies Technical Division, of the American Society for Composites in 2022. He is the recipient of the ASC Outstanding Researcher Award in Composites in 2019 and again in 202