Efficient and robust constitutive integrators for single-crystal plasticity modeling

Simulations of the dynamic deformations of metal samples require elastic-plastic constitutive updates of the material behavior to be performed over a small time step between updates, as dictated by the Courant condition. Depending on the deformation conditions, the converged time step becomes short (~$10^{-9} s$ or less). If an implicit constitutive update is applied to this class of simulation, the benefit of the implicit update is negated, and the integration is prohibitively slow. The present work recasts an implicit update algorithm into an explicit form, for which each update step is five to six times faster, and the compute time required for a plastic update approaches that needed for a fully-elastic update. For dynamic loading conditions, the explicit model is found to perform an entire simulation up to 50 times faster than the implicit model. The performance of the explicit model is enhanced by adding a subcycling algorithm to the explicit model, by which the maximum time step between constitutive updates is increased an order of magnitude. These model improvements do not significantly change the predictions of the model from the implicit form, and provide overall computation times significantly faster than the implicit form over finite-element meshes. These modifications are also applied to polycrystals via Taylor averaging, where we also see improved model performance.Comment: 27 pages, 21 figure

The State Of Health And Safety Program Management As It Pertains To OSHA In The Funeral Industry: A Formative Analysis

From a law perspective, contingency refers to possible events that may or may not happen, by which, when happening, some particular title may be affected. In the funeral industry, OSHA regulations govern a vast array of procedures directly related to day-to-day operations. If at any time one of these controls have or have not been implemented, enforced or altered, the organization could be influenced. This thesis will analyze the state of health and safety program management as it pertains to OSHA in the funeral industry

Unraveling the temperature dependence of the yield strength in single-crystal tungsten using atomistically-informed crystal plasticity calculations

We use a physically-based crystal plasticity model to predict the yield strength of body-centered cubic (bcc) tungsten single crystals subjected to uniaxial loading. Our model captures the thermally-activated character of screw dislocation motion and full non-Schmid effects, both of which are known to play a critical role in bcc plasticity. The model uses atomistic calculations as the sole source of constitutive information, with no parameter fitting of any kind to experimental data. Our results are in excellent agreement with experimental measurements of the yield stress as a function of temperature for a number of loading orientations. The validated methodology is then employed to calculate the temperature and strain-rate dependence of the yield strength for 231 crystallographic orientations within the standard stereographic triangle. We extract the strain-rate sensitivity of W crystals at different temperatures, and finish with the calculation of yield surfaces under biaxial loading conditions that can be used to define effective yield criteria for engineering design models

Influence of in-grain mesh resolution on the prediction of deformation textures in fcc polycrystals by crystal plasticity FEM

The ability of three different crystal plasticity finite element models to predict deformation textures in face-centered cubic metals observed in experiments is assessed. These methods are: (i) Taylor averaging, in which the interactions of the grains are considered in a homogenized manner; (ii) low-resolution simulation (LRS), in which grain interactions are considered explicitly albeit with low resolution; and (iii) direct numerical simulation (DNS), which provides high-resolution details of the deformation fields inside the grains and of the grain interactions. A quantitative comparison of the numerical results provided by these three methods against experimental plane-strain compression textures is performed via orientation distribution functions and fiber line analysis. It is found that some details of the texture which are inaccessible to either Taylor averaging and LRS approaches are captured by the DNS approach. This can be explained by the ability of the high-resolution DNS method to describe details of the grain interactions, including heterogeneous deformation under homogeneous macroscopic strain and smooth gradients of lattice rotations inside the grains which are missing in low-resolution models

Artificial gravity and abort scenarios via tethers for human missions to Mars

Minimum-mass tether designs are developed for a spinning human transport that not only provides artificial gravity, but also the potential for free-return aborts. The investigation reveals that severing the tether can provide a propellant-free boost to return astronauts to Earth in the event of an aborted landing on Mars. Earth–Mars–Earth, Earth–Mars–Venus–Earth, and Earth–Venus–Mars–Earth trajectories requiring little, or no, velocity change after departure from Earth, are examined. The investigation covers trajectories with launch opportunities between 2014 and 2030, launch hyperbolic excess speeds of up to 4.5 km/s and total flight times of less than 1000 days. We identify propellant-free abort scenarios in every Earth–Mars synodic period (2.14 years) with mission configurations that closely match NASA’s design reference missio