A novel foam structure is presented, which exhibits a negative Poisson's ratio. Such a material expands laterally when stretched, in contrast to ordinary materials.

http://science.sciencemag.org/content/sci/235/4792/1038.full.pdf

Foam structures with a negative poisson's ratio

Physics and phenomenology of strain hardening: the FCC case

Nature’s hierarchical materials

The mechanical behaviour of cancellous bone

Three-dimensional methods for quantification of cancellous bone architecture

The mechanical properties (elastic, plastic, creep, and fracture) of cellular solids or foams are related to the properties of the cell wall material and to the cell geometry The properties are well described by simple formulae Such materials occur widely in nature and have many potential engineering applications

The mechanical properties of cellular solids

A novel theory is presented for work hardening in stage II shown by single crystals of ductile face-centered cubic (fcc) metals. The theory is based on the assumption that slipbands are highly elongated ellipsoidal zones with weak interiors, oriented at small, alternating angles with the crystallographic slip planes. Consideration of the stacking of such ellipsoids, together with a condition for the nucleation of a new slipband at the center of an obstacle nearby, yields both the average angle of inclination and the shear offset in the bands, both of which remain constant throughout stage II. The theory makes several predictions concerning the internal stress distribution and the plastic behavior. Before expounding the theory, the concepts upon which it is based are discussed in the context of two much simpler problems: the work hardening of dispersionhardened metals and the cyclic work hardening which forms the basis of understanding fatigue properties. The picture confirms in a natural way that the value of σ
 III
 , the stress which marks the end of stage II hardening, may be taken to be equal to the fatigue endurance limit.

R. F. Mehl Medalist

Papers

The mechanical properties of cellular solids

Toward a sound understanding of dislocation plasticity