B.S. 1964 (Northwestern)
Ph.D. 1969 (Johns Hopkins)
Jenkins joined the Department of Theoretical and Applied Mechanics at Cornell in 1971 after spending two years as a research associate in Paris, France and Glasgow, Scotland where he contributed to the development of continuum theories for liquid crystals. He has held visiting positions at Sandia National Laboratory and at a number of universities: Johns Hopkins, Tokyo, Tulane, Minnesota, Florida, California at San Diego, and M.I.T. He has received distinguished fellowships from the University of Pisa, in Italy; McGill University, Montreal, Canada; and the University of Canterbury, in Christchurch, New Zealand. In March 2001, he received a honorary doctorate degree from the University of Rennes.
Recent research on granular materials has aimed at a determination of the relationship between stress and deformation in two important regimes of granular motion: slow deformations that involve enduring particle contacts and frictional forces, and rapid deformations in which momentum is assumed to be exchanged in instantaneous binary collisions between particles.
The slow deformation of granular materials is of interest in soil mechanics and geotechnical engineering. For example, the predictability of catastrophic liquefaction in loose, water-saturated sand, such as sometimes occurs during earthquakes, depends on an understanding of how discrete systems of particles interact through contact and frictional forces. The permanent deformations that occur in this regime are thought to depend on the orientational distribution of particle contacts and/or contact forces established in prior loading of the material. Anisotropy in either of these distributions is referred to as fabric, but the detailed influence of fabric on the overall stress-strain behavior of such materials has yet to be determined. A program of experiment, numerical simulation, and theoretical modeling has been initiated in order to discover which measure of fabric influences the deformation, and then to describe its evolution along relatively simple stress paths.
Rapid deformations of dry, relatively dense granular materials occur in many industrial processes and geophysical phenomena. Industrial flows include the movement of cereals, ores, and pharmaceuticals down slopes and through chutes; geophysical examples are avalanches and rock slides. Such flows proceed at densities and strain rates at which the impulsive forces of collisions between neighboring particles are responsible for the transfer of momentum in the flow. The assumption of instantaneous binary collisions between particles makes it possible to employ methods from the kinetic theory of dense gases in order to derive the balance laws and calculate the constitutive relations of continuum theories for idealized materials. Such theories have been obtained for identical, inelastic, frictional spheres and binary mixtures of such spheres. The predictions of these theories are in remarkable agreement with existing experiments and numerical simulations.
