Deformation and transformations in solids: Is there scope for a new perspective?

ABSTRACT: 

At low stresses crystalline solids deform elastically and reversibly. At high stresses irreversible plastic deformation sets in. It is now rather well established that lattice distortions and moving topological defects, known as dislocations, rule the two regimes. Affine elastic deformation and dislocations, together appear to be all one needs to explain scientifically and technologically important phenomena in crystalline solids.

On the other hand, in a variety of amorphous solids, such as foams, bulk metallic glasses, granular matter, active gels and biological materials, the situation is different. A discussion of deformation in these “soft” solids involves novel excitations, namely localized, sudden, non-affine deformations, structurally and dynamically distinct from dislocations.

Finally, real solids are neither completely crystalline nor fully amorphous. Is there a description of mechanical, structural and thermodynamic phenomena in solids which, somehow, unifies our ideas for similar processes in crystalline and amorphous matter?

In my talk, I shall briefly review some of these questions and end with some recent (and not so recent!) results obtained by me and my colleagues which present a new point of view on some of these issues.