Abstract. Graphene is a two-dimensional molecular crystal that consists of a close-packed array of carbon atoms of arbitrary in-plane extent. It has many potential applications due to its unique electronic, optical and mechanical properties. In this talk we will discuss a series of experiments that probe the mechanical properties of graphene at very large strains; monolayer and oligolayer graphene films from both exfoliated and as-grown sources will be considered. Free-standing graphene films suspended over a circular well in a silicon substrate are loaded mechanically via a diamond indenter with a tip that has a radius of about 20 nm. The distributions of the force-displacement response and the breaking force of the graphene are recorded. The elastic properties of the graphene are calculated under finite strain conditions via Density Functional Theory (DFT) calculations. The results are expressed within the context of a fifth-order Taylor series expansion of the strain energy density in order to determine the continuum non-linear anisotropic elastic properties. The finite element method is used to model the indentation process based upon this elastic model. The close correspondence between the multiscale simulations and the experiments provides experimental validation for the DFT calculations. Another set of experiments probes the magnitude of energy associated with the van der Waals force interactions between the graphene and the substrate by investigating the propensity of the graphene to adhere to the bottom of the circular well. We derive the relationship between the van der Waals energy and the geometry and residual strain of a graphene film that is partially adhered to a substrate and demonstrate how this configuration can be used to measure the van der Waals energy.

Bio. Jeffrey W. Kysar is a Professor of Mechanical Engineering at Columbia University. He received his B.S. degree from Kansas State University and his Ph.D. from Harvard University. In 2006, he received the Presidential Early Career Award for Scientists and Engineers (PECASE) which is “the highest honor bestowed by the United States government on outstanding scientists and engineers beginning their independent careers.” He received the Early Career Scientist and Engineer Award in 2006 from the Department of Energy (DOE) Office of Defense Programs. In 2001 he received the Faculty Early Career Development (CAREER) Award from the National Science Foundation. He has been named the recipient of the 2012 International Journal of Plasticity Young Researcher Award. He has been a visiting professor at the École Nationale Supérieure des Mines de Paris. His current research interests are in the field of mechanical properties of small-scale materials from a combined experimental, computational and analytical perspective. Recent projects by his research group include:  experimental characterization and theoretical development of the non-linear elastic properties of graphene and other monatomic thin film materials such as molybdenum disulfide; fabrication of crack-free blanket films of nanoporous gold onto silicon wafers for incorporation into micro-electro-mechanical systems (MEMS); fundamental study of the deformation mechanisms of monazite (lanthanum phosphate) which is a ceramic that deforms plastically; as well as the development of novel methods to characterize the spatial variation of material defects within metals that are deformed plastically.