Extracting Stress-Strain and Compressive Yield Stress Information From Spherical Indentation

Report No. ARL-TR-4229
Authors: Thomas F. Juliano; Mark R. VanLandingham; Tusit Weerasooriya; Paul Moy
Date/Pages: September 2007; 24 pages
Abstract: In recent years, instrumented indentation has become increasingly used to measure mechanical properties such as elastic modulus and fracture toughness at the micrometer scale. In this work, an experimental method is developed to estimate stress-strain behavior using indentation load-displacement and continuous stiffness measurement data. An attempt is made to subtract plastic behavior out of the loading curve to generate stress-strain data from which elastic modulus and yield stress can be determined. Indentation data generated using three indentation tips with spherical caps (20-, 50-, and 500-µm radii) are compared to bulk mechanical test data for a number of materials important for U.S. Army applications, including polycarbonate, polymethymethacrylate, a tungsten carbide ceramic composite (WC with 11.6% Cobalt), rolled-homogeneous-armor steel, and a titanium alloy (Ti Al6% V4%). The goal of this effort is to be able to predict a macroscopic stress-strain curve from a microscale test using spherical indentation while allowing the indenter to deviate from a perfect spherical shape.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2007