CRACK TIP DEFORMATION FIELDS IN ALUMINUM SINGLE CRYSTALS

Abstract eng:
The deformation fields near the tip of a crack in ductile single crystal media are studied experimentally. The crack, located between two single crystals of aluminum joined by a thin ductile interlayer of tin, is introduced via selective chemical etching and can be considered “sharp”; the material surrounding the tip is fully annealed. The crack is oriented in the crystal such that a state of plane deformation is attained in the plane normal to the crack front; this effectively renders the deformation state to be two-dimensional. A Mode I loading is applied after which the specimen is sectioned along its center plane and the in-plane rotation field under plane strain conditions is mapped using Electron Backscatter Diffraction (EBSD) in a scanning electron microscope (SEM). In essence, this measures the in-plane component of the rotation field of the displacement gradient tensor. The observations provide evidence of the main features of the deformation fields predicted by continuum single crystal plasticity, especially the existence of kink shear sector boundaries which had not been unambiguously identified in previous studies. However in order to explain the measured change in lattice rotation at the kink shear sector boundary, a dislocation structure is deduced which is different than that traditionally thought to form the kink shear sector boundary. The results have implications for analytic and numerical simulations of plastic deformation in ductile single crystal media, from the length scale of microns to the macroscopic length scale.

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