John Moosbrugger

Research Interests

Dr Moosbrugger's research focuses on plasticity and viscoplasticity of materials, including analytical/phenomenological modeling of nonproportional (biaxial), cyclic loading experiments, performing complex biaxial experiments, nonisothermal viscoplasticity model development for metals and thermomechanical behavior of semiconductor materials. Interests lie in macroscopic continuum mechanics, continuum micromechanics, and microstructural kinetics applied to constitutive equation development, fatigue life prediction and computational solid mechanics. This includes theoretical modeling using internal variable approaches at the micro- and macro-continuum levels as well as the interpretation and analysis of experimental results. Some projects are summarized below.

Cyclic Plasticity of Nickel Crystals and Polycrystals

In conjunction with Dr. David Morrison, this work focuses on relationships between dislocation substructure and cyclic plasticity modeling. Numerous experiments have been performed on fine and course grain nickel and nickel single crystals and the dislocation substructures developed under constant plastic strain amplitude, cyclic loading have been characterized. Models have been developed and correlated with differences in the fine and course grain dislocation substructures. A mixtures model has been developed for the single crystal behavior that includes explicit dislocation substructure models. This model also incorporates reverse magnetostriction, which is a ferromagnetic phenomenon. Finiite element models have been developed using the mixtures models that simulate the formation and propagation of persistent slip bands, a type of shear band localization associated with a distinct dislocation substructure.

Cyclic Plasticity and Fatigue of Ultrafine Grain Nickel

This project is aimed at achieving a fundamental understanding of low plastic strain amplitude cyclic deformation and fatigue behavior in ultra fine grain FCC metals that have a low initial dislocation density. Ultra fine grain metals are those that have grain diameters in the submicron range, but generally greater than about 10 nm. Ultra fine grain metals have been shown to exhibit exceptional strength with, in many cases, reasonable ductility. They are generally produced in one of three ways: by inert gas condensation and powder metallurgy, by severe plastic deformation of conventional grain size materials, and by electrodeposition. Materials produced by severe plastic deformation can exhibit both high strength and good ductility, but they have a very high dislocation density. Materials produced by inert gas condensation and powder metallurgy generally exhibit poor ductility. Only materials produced by electrodeposition have both low dislocation density and exhibit both high strength and good ductility. Thus, they offer potential for achieving good fatigue life characteristics relative to conventional grain size materials and ultra fine grain materials produced by other means.

Research Experience for Undergraduates: Nanoscale Science and Engineering for Materials Systems and Materials Processing. This program is designed to focus undergraduate research on an area identified as a national priority, thus providing an excellent platform for promoting graduate school among participating students. Undergraduate students participate in a ten week summer program with projects that focus either on materials processing/materials systems issues where alteration/exploitation of structure at the nanoscale is critical for achieving technological advances.