时间：2018年7月17日14:00

地点：综合1号实验楼602

The Duality of Strength and Ductility in Graphene-Metal Nanocomposites under Tensile Loading

George J. Weng

Mechanical and Aerospace Engineering

Rutgers University

New Brunswick, New Jersey 08903, USA

Several experiments have shown that, with a small amount of graphene volume concentration, the maximum strength of graphene-metal nanocomposites could increase notably while its failure strain decrease drastically, but at present no theory seems to exist to explain these opposing trends. In this paper we present a unified theory of plasticity and progressive damage, and failure to explain this duality. The theory is written in a two-scale framework, with the small scale constituting the ductile matrix and the microvoids generated during progressive damage, and the large scale combining the damaged metal matrix with 3-D randomly oriented graphene. To calculate the overall stress-strain relations the method of field fluctuation and interface effect are both considered, and to assess the evolution of microvoids during progressive damage a new damage potential is suggested. The final outcome is a simple and analytical model for the strength and ductility of the nanocomposite. We highlight the developed theory with a direct application to reduced graphene oxide/copper (rGO/Cu) nanocomposites, and demonstrate how, in line with experiments, the tensile strength can increase by 40% and the failure strain can drop from 0.39 to 0.14 as graphene volume concentration increases from 0 to 2.5 vol.%. This theory is seen to be able to explain the duality of strength and ductility in this class of nanocomposites.  

Speaker: Professor George Weng is a Distinguished Professor at Rutgers University. He received his B.S. from National Taiwan University in mechanical engineering in 1967 and Ph.D. from Yale University in engineering and applied science in 1974. He worked at Delft University of Technology, UCLA, and GM before joining Rutgers in 1977 as an Assistant Professor. He was promoted to an Associate Professor in 1980, Full Professor in 1984, and Distinguished Professor in 1992. His research interests are in the general areas of solid mechanics that connect the underlying deformation mechanisms to the overall behavior of materials. Over the years his works have touched upon the plasticity of single crystals and polycrystals, micromechanics of composite materials, shape-memory alloys, ferroelectric ceramics, magnetoelectric coupling, nanocrystalline solids, and electrical and thermal conductivity of CNT- and graphene-based nanocomposites. He has published 226 referred journal articles, written 8 book chapters, and edited 5 books. His Google Scholar citations are 9,552 with an h-index of 50, and Web of Science citations are 6,295 with an h-index of 42. He has been an Editor of Acta Mechanica since 1985, and was the Editor of Journal of Engineering Materials and Technology from 1992-1997. He also served as Chairman of ASME Materials Division during 1993-1994. He is a Fellow of ASME, a Fellow of American Academy of Mechanics, and an Honorary Life Member of Society of Engineering Science. In recognition of his fundamental contributions in theoretical solid mechanics, he was awarded the prestigious William Prager Medal in 2013.