1. A mechanical structure comprising: a crystalline superelastic alloy characterized by an average grain size and exhibiting a martensitic phase transformation resulting from a mechanical stress input greater than a characteristic first critical stress; and a configuration of the superelastic alloy providing a geometric structural feature of the alloy having an extent that is no greater than about 200 micrometers and that is no larger than the average grain size of the alloy, the geometric feature undergoing the martensitic transformation without intergranular fracture of the geometric feature.