Nanoindentation near the edge
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C.R. Frihart, J.F. Beecher, and R.J. Moon United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726
P.J. Resto and Z.H. Melgarejo Materials Science Program, University of Wisconsin—Madison, Madison, Wisconsin 53706
O.M. Sua´rez Engineering Science and Materials Department, University of Puerto Rico—Mayagu¨ez, Mayagu¨ez, Puerto Rico 00681-9044
H. Baumgart Applied Research Center, Jefferson National Accelerator Facility, Newport News, Virginia 23606; and Department of Electrical Engineering, Old Dominion University, Norfolk, Virginia 23529
A.A. Elmustafa Applied Research Center, Jefferson National Accelerator Facility, Newport News, Virginia 23606; and Department of Mechanical Engineering, Old Dominion University, Norfolk, Virginia 23529
D.S. Stonea) Materials Science Program, University of Wisconsin—Madison, Madison, Wisconsin 53706; and Department of Materials Science and Engineering, University of Wisconsin—Madison, Madison, Wisconsin 53706 (Received 31 July 2008; accepted 4 November 2008)
Whenever a nanoindent is placed near an edge, such as the free edge of the specimen or heterophase interface intersecting the surface, the elastic discontinuity associated with the edge produces artifacts in the load–depth data. Unless properly handled in the data analysis, the artifacts can produce spurious results that obscure any real trends in properties as functions of position. Previously, we showed that the artifacts can be understood in terms of a structural compliance, Cs, which is independent of the size of the indent. In the present work, the utility of the SYS (Stone, Yoder, Sproul) correlation is demonstrated in its ability to remove the artifacts caused by Cs. We investigate properties: (i) near the surface of an extruded polymethyl methacrylate rod tested in cross section, (ii) of compound corner middle lamellae of loblolly pine (Pinus taeda) surrounded by relatively stiff wood cell walls, (iii) of wood cell walls embedded in a polypropylene matrix with some poorly bonded wood–matrix interfaces, (iv) of AlB2 particles embedded in an aluminum matrix, and (v) of silicon-on-insulator thin film on substrate near the free edge of the specimen.
I. INTRODUCTION
The most widely used analysis for generating hardness and modulus data from nanoindentation measurements is the method of Oliver and Pharr.1 Three implicit assumptions behind the method are that the material being tested has rigid support, that it fill a half-space, and that it be homogeneous. When these assumptions are satisfied, the long-range elastic displacements can be estimated based on a Sneddon-type theory for indentation of an elastic a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0076
1016
J. Mater. Res., Vol. 24, No. 3, Mar 2009
half-space by a cone.2–4 When these assumptions are not satisfied—which is the case for most of the interesting specimens studied these days—Sneddon’s theory breaks down, and the utility of the Oliver–Pharr analysis becomes compromised. For instance
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