Unsupervised Learning-Based Multiscale Model of Thermochemistry in 1,3,5-Trinitro-1,3,5-triazinane (RDX).

The response of high-energy-density materials to thermal or mechanical insults involves coupled thermal, mechanical, and chemical processes with disparate temporal and spatial scales that no single model can capture. Therefore, we developed a multiscale model for 1,3,5-trinitro-1,3,5-triazinane, RDX, where a continuum description is informed by reactive and nonreactive molecular dynamics (MD) simulations to describe chemical reactions and thermal transport. Reactive MD simulations under homogeneous isothermal and adiabatic conditions are used to develop a reduced-order chemical kinetics model.

Engineering curvature in graphene ribbons using ultrathin polymer films.

We propose a method to induce curvature in graphene nanoribbons in a controlled manner using an ultrathin thermoset polymer in a bimaterial strip setup and test it via molecular dynamics (MD) simulations. Continuum mechanics shows that curvature develops to release the residual stress caused by the chemical and thermal shrinkage of the polymer during processing and that this curvature increases with decreasing film thickness; however, significant deformation is only achieved for ultrathin polymer films. Quite surprisingly, explicit MD simulations of the curing and annealing processes show that the predicted trend not just continues down to film thicknesses of 1-2 nm but that the curvature development is enhanced significantly in such ultrathin films due to surface tension effects.

Dislocation structures and the deformation of materials.

We present results from phase-field simulations of a two-dimensional model of dislocation microstructure development under increasing strain that incorporates the effects of the full, three-dimensional, microstructure in an approximate way. Despite its simplicity, the model yields quantitative predictions of both the deformation properties of face-centered cubic metals as well as key descriptors of the evolving microstructure over a wide range of stress and strain. The present results have important implications for how we interpret and describe the deformation properties of fcc materials.

Avalanches and scaling in plastic deformation.

Plastic deformation of crystalline materials is a complex nonhomogeneous process characterized by avalanches in the motion of dislocations. We study the evolution of dislocation loops using an analytically solvable phase-field model of dislocations for ductile single crystals during monotonic loading. The distribution of dislocation loop sizes is given by P(A) approximately A-sigma, with sigma=1.