| The paper first reviews some - partly unknown - initial observations made by the second author and his Michigan Tech colleagues in an effort to capture the basic deformation mechanisms at the nanoscale for developing corresponding scale-dependent gradient elasticity, gradient plasticity and gradient fracture models. Their two main conclusions - i.e. the emergence of two co-existing phases (bulk and grain boundary) and the dominance of nanovoid formation and material rotation as opposed to material slip - are then used to motivate some metal physics and strength of materials models for interpreting the associated experimental findings, as well as the construction of gradient continuum mechanics models (nanoelasticity, nanoplasticity) to be used in relation to the formulation and solution of related boundary value problems at the nanoscale. Finally, the aforementioned observations on grain rotation - in conjunction with the standard theory of defects, as employed recently by the first author and his coworkers - is used to describe rotation dependent strengthening/softening mechanisms in nanopolycrystals weakened by cracks. |
full paper (pdf, 1552 Kb)