Special rotational deformation as a toughening mechanism in nanocrystalline solids

A theoretical model is suggested which describes the effect of special rotational deformation on crack growth in deformed nanocrystalline ceramics and metals. Within the model, the special rotational deformation (driven by the external stress concentrated near the tip of a mode I crack) occurs in a nanograin through formation of immobile disclinations whose strengths gradually increase during the formation process conducted by grain boundary sliding and diffusion. The special rotational deformation releases, in part, local stresses near the crack tip, thus serving as a toughening mechanism in nanocrystalline materials. The effects of the special rotational deformation on the growth of pre-existent, comparatively large cracks in nanocrystalline metals and ceramics are estimated.