MSE Colloquium: George Pharr, Probing the Mechanical Behavior of Hard, Brittle Materials with Nanoindentation

Chancellor's Professor, McKamey Professor of Engineering, and UT-ORNL Joint Faculty

All dates for this event occur in the past.

264 MacQuigg Labs
105 W. Woodruff Ave
Columbus, OH 43210
United States

Abstract

Since its development in the mid-1980's, nanoindentation has proven itself to be an important tool for measuring and characterizing the mechanical behavior of a wide variety of materials at the micron and submicron scales. Among the properties that are routinely measured are hardness, elastic modulus, fracture toughness, yield strength, work hardening, residual stress, and the time-dependent parameters characteristic of viscoelasticity and creep. After briefly reviewing the basics of the nanoindentation and the wide range of applications in which the technique has proven useful, this presentation focuses on how nanoindentation can be used to characterize the mechanical behavior of hard, brittle materials like ceramics, glasses, and semiconductors. One problem encountered in testing such materials in ordinary uniaxial tension and compression tests is that they fail catastrophically before flowing plastically. However, because of the high hydrostatic pressures produced during indentation contact, nanoindentation offers a unique way to induce plasticity in brittle materials, and, in combination with finite element simulation, can be used to estimate their yield strengths and work hardening behavior. In addition, the well-known median-radial cracking that occurs during the indentation of brittle materials with sharp pyramidal indenters such as the Vickers and Berkovich has traditionally been used as a way to estimate their fracture toughness, albeit with some controversy. Here, cohesive zone finite element simulations are used to show how and why some of the controversy arises as well as how it can conceivably be corrected.   

Work supported by the National Science Foundation under grant number CMMI 0926798, and by the US Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.

 

 

George M. Pharr
George M. Pharr

Bio

George M. Pharr is Chancellor's Professor and McKamey Professor of Engineering at the University of Tennessee, Knoxville (UT). He also holds a Joint Faculty position in the Materials Science and Technology Division at the Oak Ridge National Laboratory (ORNL). He received his BS in Mechanical Engineering at Rice University in 1975 and Ph.D. in Materials Science and Engineering from Stanford in 1979. After one year of postdoctoral study at the University of Cambridge, England, he returned to Rice in 1980 as a faculty member in the Department of Mechanical Engineering and Materials Science. He moved to his current joint position at UT and ORNL in 1998 and served as Head of the UT Materials Science and Engineering Department during the period 2006-2011. He is currently the Director of the UT/ORNL Joint Institute for Advanced Materials.

Dr. Pharr received ASM International’s Bradley Stoughton Award for Young Teachers of Metallurgy in 1985. His honors also include the Amoco Award for Superior Teaching at Rice University in 1995, the University of Tennessee Chancellor's Award for Research and Creative Achievement in 2004, a Humboldt Senior Scientist Award in 2007, and the Materials Research Society's inaugural Innovation in Materials Characterization Award in 2010. He is a member of the National Academy of Engineering (2014), a Fellow of ASM International (1995), and a Fellow of the Materials Research Society (2012). Dr. Pharr has been an Associate Editor of the Journal of the American Ceramic Society since 1990 and Principal Editor of the Journal of Materials Research since 2012. He is an author or co-author of more than 200 scientific publications, including 4 book chapters. His research focuses on mechanisms of plasticity and fracture in solids, especially at small scales.