Every theory of superconductivity can be disproved! This tongue-in-cheek theorem struck a chord when Felix Bloch announced it in the early 1930s. Virtually every major physicist then working on theory—including Bloch, Niels Bohr, Wolfgang Pauli, Werner Heisenberg, Lev Landau, Leon Brillouin, W. Elsasser, Yakov Frenkel, and Ralph Kronig—had tried and failed to explain the mysterious phenomenon in which below a few degrees kelvin certain metals and alloys lose all their electrical resistance. The frequency with which Bloch's theorem was quoted suggests the frustration of the many physicists who were struggling to explain superconductivity.

Neither the tools nor the evidence were yet adequate for solving the problem. These would gradually be created during the 1940s and 1950s, but bringing them to bear on superconductivity and solving the long-standing riddle required a special set of talents and abilities: a deep understanding of quantum mechanics and solid-state physics, confidence in the solubility of the problem, intuition about the phenomenon, a practical approach to problem-solving, patience, teamwork, and above all refusal to give up in the face of repeated failures. When John Bardeen took on the problem of superconductivity in the late 1930s, he held it like a bulldog holds a piece of meat, until he, his student J. Robert Schrieffer, and postdoctoral candidate Leon Cooper solved it in 1957.

Ductility is defined as the ability of a material to change shape without fracture. It is of critical importance for engineering materials for both manufacturability and Performance. Measures of ductility include percent elongation (uniform plastic flow prior to mechanical instability—necking—or fracture) and percent reduction in area. Fracture toughness is also some measure of potential ductility. Engineering materials exhibit wide variations in ductility which can often limit their application.

Ductility is a property of nanocrystalline materials which might be predicted to be enhanced by extrapolation of its grain-size dependence in conventional polycrystalline materials. It has been predicted that extrapolation of the grain size, or the scale of the microstructure, to the nanoscale will lead to both strengthening and an increase in ductility. As far as failure and ductility are concerned, this idea is based on experience with conventional materials, where the yield and fracture stress show different dependencies on the grain size. The fracture stress typically increases faster than the yield stress with decreasing grain size such that ductile/brittle transitions can occur. For example, the ductile / brittle transition temperature in mild steel can be lowered about 40°C by reducing the grain size by a factor of five. In terms of how ductility may be affected by the extreme grainsize reduction to the nanoscale, we consider the following. Firstly, it may be recalled that obtaining ductility relies simply on plastic deformation occurring without the catastrophic onset of failure mechanisms, and therefore we can examine possibilities of changing ductility in terms of avoiding failure.