Plenary Lectures

Alan Needleman
Professor of Mechanics of Solids and Structures
Division of Engineering
Brown University

Plenary Title:

Micro and Macro Modeling of Contact and Friction

Plenary Abstract:

Contact and frictional sliding of a surface between two solids governs a range of socially and technologically important mechanical behaviors and failure mechanisms over a wide range of size scales, from micro-machines to earthquakes. The classical Amontons-Coulomb description of friction, which has been widely used both to determine service behavior and to organize experimental measurements, states that the shear force along an interface is proportional to the normal force, with the proportionality constant being the coefficient of friction. Despite its successes, there are fundamental problems with the Amontons-Coulomb description of friction: (i) experiments have shown that friction is both time and slip distance dependent; and (ii) analyses have shown that with this description sliding along an interface between dissimilar elastic solids is, in a wide range of circumstances, an ill-posed problem. Motivated these results, phenomenological rate and state frictional constitutive relations have been developed. Some macro scale analyses illustrating consequences that emerge from a rate and state description of sliding will be presented. The micro scale analyses presented will focus on size effects in the contact and sliding of unlubricated surfaces of crystalline solids that deform plastically by dislocation glide. The prospects for using the micro scale analyses to develop macro scale frictional constitutive relations will be briefly discussed.

Biographical Information:

Professor Needleman’s main research interests are in the computational modeling of deformation and fracture processes in structural materials, in particular metals. A general objective is to provide quantitative relations between the measurable (and hopefully controllable) features of the materials’ micro-scale structure and its macroscopic mechanical behavior. Ongoing research projects involve studies of ductile fracture and ductile-brittle transitions; crack growth in heterogeneous microstructures with particular emphasis on the role of interfaces; nonlocal and discrete dislocation plasticity; fatigue crack growth; and fast fracture in brittle solids.

Professor Needleman is a Member of the National Academy of Engineering, a Fellow of the American Society of Mechanical Engineers, a Fellow of the American Academy of Mechanics, an Honorary Member of MECAMAT (Groupe Français de Mecanique des Matériaux) and a Foreign Member of the Danish Center for Applied Mathematics and Mechanics. He has been recognized by ISI (Science Citation Index) as a highly cited author both in Engineering and in Materials Science. In 1994, his work on 3D modeling of metallic fracture was a finalist in the Science Category for the Computerworld-Smithsonian Award.