题目：Indentation Deformation of Thin Films
Surface damage and interfacial failure may deteriorate the performance of multilayer systems and limit the reliability of devices. Knowledge of the mechanical properties of multilayer structures is critical to design and fabricate these layered structures and devices. Indentation is one of the techniques used in measuring mechanical properties of small-volume structures, such as thin films and surface coatings. Analysis of the indentation tests is generally based on the Oliver-Pharr method, which uses the analytical solutions for the contact between two solid spheres or between a rigid indenter and an elastic half-space. This has limited the application of the O-P method in evaluating mechanical properties of small-volume structures. We present a rigorous analysis of an incompressible elastic thin film indented by a rigid spherical or conical indenter under conditions that the contact radius is much larger than the film thickness and the contact condition between the indenter and the film is frictionless. Closed-form solutions for the load–displacement relationship and the contact stiffness are derived in terms of the ratio of the contact radius to the film thickness and material properties. We use indentation to study the indentation deformation of low modulus, ultrathin polymeric films with thicknesses of 47, 125 and 3000 nm on a silicon wafer. The nominal reduced contact modulus increases with the indentation load and indentation depth due to the effect of substrate. The effect of substrate on the reduced contact modulus is described by an elastic contact model for indentations with larger contact radius than the film thickness.
Prof. Fuqian Yang received his B.S. in Engineering Physics from Tsinghua University, M.S. in Mechanical Engineering and Ph.D in Materials Science and Engineering from the University of Rochester. He is a full professor in Department of Chemical and Materials Engineering at the University of Kentucky. Dr. Yang’s research focuses on electrical-chemical-mechanical behavior of advanced materials and published more than 250 scientific articles, including creep behavior of materials, adhesive deformation of materials, electromechanical interaction of materials, whisker growth, and stress-diffusion interaction in lithium-ion batteries.