Density-functional-theory-based local quasicontinuum method: Prediction of dislocation nucleation

We introduce the density functional theory (DFT) local quasicontinuum method: a first principles multiscale material model that embeds DFT unit cells at the subgrid level of a finite element computation. The method can predict the onset of dislocation nucleation in both single crystals and those with inclusions, although extension to lattice defects awaits new methods. We show that the use of DFT versus embedded-atom method empirical potentials results in different predictions of dislocation nucleation in nanoindented face-centered-cubic aluminum

Density-functional-theory-based local quasicontinuum method: Prediction of dislocation nucleation

We introduce the density functional theory (DFT) local quasicontinuum method: a first principles multiscale material model that embeds DFT unit cells at the subgrid level of a finite element computation. The method can predict the onset of dislocation nucleation in both single crystals and those with inclusions, although extension to lattice defects awaits new methods. We show that the use of DFT versus embedded-atom method empirical potentials results in different predictions of dislocation nucleation in nanoindented face-centered-cubic aluminum

A Constrained Sequential-Lamination Algorithm for the Simulation of Sub-Grid Microstructure in Martensitic Materials

We present a practical algorithm for partially relaxing multiwell energy densities such as pertain to materials undergoing martensitic phase transitions. The algorithm is based on sequential lamination, but the evolution of the microstructure during a deformation process is required to satisfy a continuity constraint, in the sense that the new microstructure should be reachable from the preceding one by a combination of branching and pruning operations. All microstructures generated by the algorithm are in static and configurational equilibrium. Owing to the continuity constrained imposed upon the microstructural evolution, the predicted material behavior may be path-dependent and exhibit hysteresis. In cases in which there is a strict separation of micro and macrostructural lengthscales, the proposed relaxation algorithm may effectively be integrated into macroscopic finite-element calculations at the subgrid level. We demonstrate this aspect of the algorithm by means of a numerical example concerned with the indentation of an Cu-Al-Ni shape memory alloy by a spherical indenter.Comment: 27 pages with 9 figures. To appear in: Computer Methods in Applied Mechanics and Engineering. New version incorporates minor revisions from revie

Prediction Of Dislocation Nucleation During

We introduce the Orbital-Free Density Functional Theory Local Quasicontinuum (OFDFT-LQC) method: a first-principles-based multiscale material model that embeds OFDFT unit cells at the subgrid level of a finite element computation. Although this method cannot address intermediate length scales like grain boundary evolution or microtexture, it is well suited to study material phenomena such as continuum level prediction of dislocation nucleation and the e#ects of varying alloy composition. The model is illustrated with the simulation of dislocation nucleation during indentation into the (111) and (110) surfaces of aluminum, and compared against results obtained using an Embedded Atom Method (EAM) interatomic potential. None of the traditional dislocation nucleation criteria (Hertzian principal shear stress, actual principal shear stress, von Mises strain or resolved shear stress) correlate with a previously proposed local elastic stability criterion, #. Discrepancies in dislocation nucleation predictions between OFDFT-LQC and other simulations highlight the need for accurate, atomistic constituitive models and use of realistically-sized indenters in the simulations. Key words. Multiscale modelling, indentation, dislocation nucleation, embedded atom method, density functional theory

The 2018 Lake Louise Acute Mountain Sickness Score

The Lake Louise Acute Mountain Sickness (AMS) scoring system has been a useful research tool since first published in 1991. Recent studies have shown that disturbed sleep at altitude, one of the five symptoms scored for AMS, is more likely due to altitude hypoxia per se, and is not closely related to AMS. To address this issue, and also to evaluate the Lake Louise AMS score in light of decades of experience, experts in high altitude research undertook to revise the score. We here present an international consensus statement resulting from online discussions and meetings at the International Society of Mountain Medicine World Congress in Bolzano, Italy, in May 2014 and at the International Hypoxia Symposium in Lake Louise, Canada, in February 2015. The consensus group has revised the score to eliminate disturbed sleep as a questionnaire item, and has updated instructions for use of the score