Professor John Bassani, Dept. of Mechanical Engineering and Applied Mechanics at Penn, will present a talk: “Effects of Microstructural Evolution on Strain Localization and Ductile Failures.”
Abstract: Virtually all solid materials deformed at moderate to large strains undergo changes in their microstructures that continuously alter material symmetries and can significantly affect macroscopic response. Reasonably tractable models have been lacking, which explains limited success in predicting, for example, forming processes such as drawing and stamping. Material systems of interest include polycrystals, composites, porous materials, and viscoelastic fluids. A model is developed for a class of anisotropic elastic-plastic solids in which the orthotropic triad that characterizes material symmetry evolves with deformation. In essence, microstructural evolution arises from non-coaxiality between the plastic rate of stretching and the orthotropic axes, which intuitively makes sense. That key result is established rigorously from representation theory for tensor-valued functions. The resulting phenomenological theory extends classical theories of plasticity to include the spatially-varying evolution of material symmetries under large strain deformation. Comparisons of the phenomenological model with both experimental data and micromechanical models for polycrystals are in very good agreement for variuos alloys and form the basis for simulations of complex deformation processes. Significant effects of microstructural evolution on strain localization are predicted from analyses of necking, shear banding, and buckling, which demonstrates why analyses that neglect those effects have proven inadequate. That knowledge is crucial from an industrial perspective and as a starting point in the DOE Grand Challenge of light-weighting transportation systems to reduce green-house gases from. Other applications are additive manufacturing and the flow of complex fluids.