Crack tip deformation fields in ductile single crystals

Abstract Crack tip deformation fields 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. After a Mode I loading is applied, the specimen is sectioned and the in-plane rotation field under plane strain conditions is mapped using Electron Backscatter Diffraction. The observations provide evidence of the main features of the deformation fields predicted by Rice (Mech Mater 6 (1987) 317) using continuum single crystal plasticity, especially the existence of kink shear sector boundaries which had not been unambiguously identified in previous studies. However to explain the measured change in lattice rotation at the kink shear sector boundary, an alternate dislocation structure is deduced which does not require a high concentration of dislocation sources to be distributed along the ray of the putative kink shear sector boundary. Based on this, a lower bound on the dislocation density in the kink shear sector is established experimentally. The results have implications for analytical and numerical simulations of plastic deformation in ductile single crystal media, from the length scale of microns to the macroscopic length scale.