618 research outputs found
Dislocation subgrain structures and modeling the plastic hardening of metallic single crystals
A single crystal plasticity theory for insertion into finite element simulation is formulated using sequential laminates to model subgrain dislocation structures. It is known that local models do not adequately account for latent hardening, as latent hardening is not only a material property, but a nonlocal property (e.g. grain size and shape). The addition of the nonlocal energy from the formation of subgrain structure dislocation walls and the boundary layer misfits provide both latent and self-hardening of a crystal slip. Latent hardening occurs as the formation of new dislocation walls limits motion of new mobile dislocations, thus hardening future slip systems. Self-hardening is accomplished by an evolution of the subgrain structure length scale. The substructure length scale is computed by minimizing the nonlocal energy. The minimization of the nonlocal energy is a competition between the dislocation wall energy and the boundary layer energies. The nonlocal terms are also directly minimized within the subgrain model as they affect deformation response. The geometrical relationship between the dislocation walls and slip planes affecting the dislocation mean free path is taken into account, giving a first-order approximation to shape effects. A coplanar slip model is developed due to requirements while modeling the subgrain structure. This subgrain structure plasticity model is noteworthy as all material parameters are experimentally determined rather than fit. The model also has an inherit path dependence due to the formation of the subgrain structures. Validation is accomplished by comparison with single crystal tension test results
Wear behavior of a microhybrid composite vs. a nanocomposite in the treatment of severe tooth wear patients:A 5-year clinical study
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Fatal nevirapine-induced Stevens-Johnson syndrome with HIV-associated mania
Mania with psychotic features is one of the common presenting clusters of psychiatric symptoms in HIV-infected patients. Commonly, patients with HIV-associated mania receive antiretroviral treatment, mood stabilisers and antipsychotics. This case of Stevens-Johnson syndrome highlights the dilemmas and complications that may arise when prescribing multiple medications in HIV-associated psychiatric disorders
Leiomyosarcoma of the Great Saphenous Vein: A Case Report and Review of the Literature
Introduction: Leiomyosarcoma of the venous system is rare, even more so in the greater saphenous vein. In the 85 years since
van Ree described the first case in 1919 only 25 cases have been reported in the world
Data-Driven Statistical Reduced-Order Modeling and Quantification of Polycrystal Mechanics Leading to Porosity-Based Ductile Damage
Predicting the process of porosity-based ductile damage in polycrystalline
metallic materials is an essential practical topic. Ductile damage and its
precursors are represented by extreme values in stress and material state
quantities, the spatial PDF of which are highly non-Gaussian with strong fat
tails. Traditional deterministic forecasts using physical models often fail to
capture the statistics of structural evolution during material deformation.
This study proposes a data-driven statistical reduced-order modeling framework
to provide a probabilistic forecast of the deformation process leading to
porosity-based ductile damage, with uncertainty quantification. The framework
starts with computing the time evolution of the leading moments of specific
state variables from full-field polycrystal simulations. Then a sparse model
identification algorithm based on causation entropy, including essential
physical constraints, is used to discover the governing equations of these
moments. An approximate solution of the time evolution of the PDF is obtained
from the predicted moments exploiting the maximum entropy principle. Numerical
experiments based on polycrystal realizations show that the model can
characterize the time evolution of the non-Gaussian PDF of the von Mises stress
and quantify the probability of extreme events. The learning process also
reveals that the mean stress interacts with higher-order moments and extreme
events in a strongly nonlinear and multiplicative fashion. In addition, the
calibrated moment equations provide a reasonably accurate forecast when applied
to the realizations outside the training data set, indicating the robustness of
the model and the skill for extrapolation. Finally, an information-based
measurement shows that the leading four moments are sufficient to characterize
the crucial non-Gaussian features throughout the entire deformation history
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