Bridging Scales – A Coarse-Grained Modeling Framework for Simulating Fracture in Epoxy Resin and Composites

Julian Konrad

Computer Chemistry Center, FAU

14. June 2023, 17:00
WW8, Room 2.018-2, Dr.-Mack-Str. 77, Fürth

Polymer modeling across time and length scales can bridge the gap from molecular considerations to the design of macroscopic components and requires understanding in a broad spectrum of physical and chemical phenomena. Quantum mechanical (QM) calculations provide the basis for the formation of atomistic polymer networks on the nano-scale with respect to thermodynamics. Monitoring dynamic processes along fracture by means of molecular dynamics (MM) enable development of coarse-grained models (CG).

We investigated the epoxy system of bisphenol F diglycidyl ether (BFDGE) and 4,6-diethyl-2- methylbenzene-1,3-diamine (DETDA) regarding the crosslinking reaction, as well as bond dissociation, by development of a reactive Force Field, which facilitates our curing algorithm to reach the experimental crosslinking degree of 99% [1, 2]. The resulting, reliable models fulfill bulk, especially the elastic properties, we derived from linear response theory [3]. Furthermore, we studied tensile deformation about inter-molecular reorganization processes along fracture processes and extrapolated occurring stresses to vanishing strain rates, which yielded in accordance with macroscopic specimens [2,3]. We also accomplished the transfer from molecular simulation to constitutive modeling by means of a multi-scale modeling capturing deformation and damage in epoxy resins [4]. Addressing the interplay of composite materials, we studied molecular structuring of epoxy at silica and cellulose interfaces [5] as well as corresponding forces along detaching processes [6]. In conclusion, there is a large body of atomistic-level insights available to provide the needed inputs for a coarse-grained setup. Hence this setup directly features the beforehand identified properties from QM and MM methods and the final particle-based model enables analysis up to the µm-scale and opens up a variety of possibilities to analyze fracture using physical quantities or graph-theoretical methods.

[1] Robert H. Meißner, Julian Konrad, Benjamin Boll, Bodo Fiedler, and Dirk Zahn. “Molecular Simulation of Thermosetting Polymer Hardening: Reactive Events Enabled by Controlled Topology Transfer”. Macromolecules, 53(22): 9698 – 9705, November 2020.

[2] Julian Konrad, Robert H. Meißner, Erik Bitzek, and Dirk Zahn. “A Molecular Simulation Approach to Bond Reorganization in EpoxyResins: From Curing to Deformation and Fracture”. ACS Polymers Au, 1(4): 165 – 174, December 2021.

[3] Julian Konrad and Dirk Zahn. “Assessing the mechanical properties of molecular materials from atomic simulation”. AIMS Materials Science, 8(6):867 – 880, December 2021.

[4] Julian Konrad, Sebastian Pfaller and Dirk Zahn. “Multi-Scale Modelling of Plastic Deformation, Damage and Relaxation in Epoxy Resins”. Polymers, 14(16): 32 – 40, August 2022.

[5] Julian Konrad, Paolo Moretti and Dirk Zahn. “Molecular Simulations and Network Analyses of Surface/Interface Effects in Epoxy Resins: How Bonding Adapts to Boundary Conditions”. Polymers, 14(19): 2073 -4360, September 2022.

[6] Julian Konrad and Dirk Zahn. “Interaction Forces in reinforced Epoxy Resins: from molecular Scale Understanding towards meso-scale Interfaces”. submitted, 2023.

.