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It is known that nanocrystallites can form in shear bands produced during severe bending or high-energy ball milling of thin ribbons of a metallic glass. We present direct experimental evidence that highly confined and controlled local contact at the ultrafine scale in the form of quasi-static nanoindentation of a bulk glassy metal alloy at room temperature can also cause nanocrystallization. Atomic force microscopy and transmission electron microscopy show that nanocrystallites nucleate in and around shear bands produced near indents and that they are the same as crystallites formed during annealing without deformation at 783 kelvin. Analogous to results from recent experiments with glassy polymers, our results are reasoned to be a consequence of flow dilatation inside the bands and of the attendant, radically enhanced, atomic diffusional mobility inside actively deforming shear bands., The structure, thermodynamic stability, and electrical and magnetic properties of thin ribbons of amorphous metal alloys have been the focus of many theoretical and experimental investigations (1-6). With the development [...]

The source and the effects of strain-induced heating on the stress-strain behavior and corresponding cold drawing process of glassy polymers are investigated. The nature of dissipative and stored components of work are discussed where only 50 to 80% of the mechanical work of glassy polymers has been found to be dissipative. This phenomenon is demonstrated to be well-modeled by considering a portion of the work to be stored as strain-induced molecular orientation in the polymer that evokes a back stress tensor. The results of the modeling are found to be consistent with experimental measurements reported in the literature. The constitutive and corresponding heat generation model are used in fully thermo-mechanically coupled finite element analysis of the cold drawing of glassy polymers. The influence of applied elongation rate on the resulting temperature rise, heat transfer, thermal softening, and fiber geometry are presented, together with a full complement of the deformation field parameters related to the propagating shoulders of the drawn neck.

The factors that contribute to the occurence of the dominant failure process in structural alloys under various load conditions are studied. The effects of two distinct failure modes, namely the net section creep rupture process and creep crack growth process, on the eventual fracture of a material are evaluated through numerical analysis. Results indicate that the level of macroscopic defect, such as crack, is dependent on the material's ductile properties.

The analysis of crack deflection along interfaces for increased fiber composite toughness requires the development of a crack deflection criteria that considers the elastic anisotropy of fibers. Two aligned orthotropic media are used for deflection analysis. Material parameters affecting the stress and deformation fields and the delamination criterion are discussed. Generalized delamination charts can also be obtained as a function of a bi-material constant to represent the elastic dissimilarity of the two media.

The mechanisms of brittle-to-ductile transition of fracture in intrinsically brittle crystalline solids such as structural steel is of great technological interest for a long time. A renewed level of interest has resulted in a number of fundamental studies of both experimental nature and modeling of crack-tip response which demonstrated a remarkable connection of atomic atomic level processes at tips of cleavage cracks and macroscopic fracture transitions.