MedeA® Application Notes for Automotive

The effect of resin molecular architecture on the small strain elastic constants of diamine-cured epoxy thermosets has been studied using classical all-atom simulations conducted within the MedeA simulation environment. Batches of thermoset systems have been created using chemically similar di, tri and tetrafunctional resins, followed by calculation of stiffness and compliance matrices for each individual model. Analysis of the batches of topologically and geometrically distinct structures using the Hill-Walpole approach yields upper and lower bounds estimates of the moduli differing by typically 1%, enabling critical comparison with experimentally-measured values.

Effect of Resin Molecular Architecture on Epoxy Thermoset Mechanical Properties

The stress-strain behavior of a Cu nanowire is simulated with the MedeA environment using a quasi-classical embedded atom potential and the LAMMPS molecular dynamics code. The monocrystalline wire has a diameter of 3.3 nm and is stretched in the [100] direction. The simulations show an initial elastic region with a linear increase in stress, which reaches a maximum just before the onset of slip in (111) planes. Upon further strain the model reveals the formation of more slip planes and necking until the break point is reached.

Stress-Strain Behavior of a Cu Nanowire Simulated with MedeA-LAMMPS

The temperature-induced phase transition from monoclinic to tetragonal ZrO₂ is predicted from first principles calculations using a quasi-harmonic approach for the vibrational enthalpy and entropy. The computed transition temperature is within 15% of the experimental value. Relative trends due to vacancies, alloying elements, and mechanical stress can be expected to have a higher accuracy. The present results show the importance of thermal expansion, which is here also obtained from first principles.

Temperature-Dependent Phase Transitions of ZrO₂

Interfaces are present in most materials and have a large impact on mechanical properties such as stiffness and yield strength. Given that the properties of an interface can radically change by the presence of even minute amounts of impurities, it is of great interest to predict the effect of segregated atoms at interfaces.

As systematic experimental information on the impact of specific defect types on the grain boundary strength is hard to obtain, computational modelling is of great help.

Strength of Ni Grain Boundary and the Effect of Boron

Accurate measurements of diffusion coefficients of atoms in solids are difficult and deviations between different experiments can be several orders of magnitude. For the benchmark case of hydrogen diffusion in nickel first-principles calculations give a remarkable agreement with available experimental data especially near room temperature. Thus, computations of diffusion coefficients can be comparable in reliability with measured data. Simulations are possible for situations such as high strain, or slow processes where measurements are difficult or impractical.

Diffusion of Hydrogen in Nickel

First-principles calculations reveal a three-fold increase in the Young’s modulus of graphite as it is lithiated (C→LiC₆). A linear expression is determined that describes the approximate stiffness of Li intercalated graphite as a function of loading which may lead to greatly improved continuum models of electrode deformation and failure.

Graphite Electrode Elastic Properties upon Li Intercalation

Hydrides containing alkaline-earth metals are prototypes for hydrogen storage materials. For this purpose the heat of formation and the mechanical properties are of fundamental interest. First- principles electronic structure methods provide systematic values for these materials properties. The agreement with experimental data for the heat of formation is good. Presently, no experimental data for the elastic coefficients of these metal hydrides are available thus leaving the computed data as the sole source.

Alkaline-earth hydrides