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Experimental Mechanics

, Volume 50, Issue 4, pp 545–552 | Cite as

Macro- to Nano-indentation Hardness Stress–Strain Aspects of Crystal Elastic/Plastic/Cracking Behaviors

  • R. W. ArmstrongEmail author
  • W. L. Elban
Article

Abstract

Single crystal KCl and MgO indentation hardness test results spanning macroscopic, microstructural, and nanoscale measurements are brought together in a ball-indenter-based stress–strain description. For a significant range of hardness measurements made on MgO (001) crystal surfaces, increasingly greater plastic flow stresses are determined at smaller loads applied to smaller effective ball sizes at the rounded tips of Berkovich indenters; and, at the smallest ball diameters of 3,200 nm and 400 nm, the plastic flow stresses are shown to approach the predicted Hertzian elastic loading stresses. The resultant hardness stress–strain description, that is extended to cover the elastic, plastic, and cracking behaviors of MgO crystals, is usefully applied also to a comparison of indentation test results reported for NaCl and RDX crystals. In general, the dislocation-induced cracking stress measurements are shown for MgO and RDX crystals to be lower than cracking stresses evaluated on an (elastic) indentation fracture mechanics (IFM) basis. Comparison is made with metal nanoindentation hardness test results.

Keywords

Ball indentation hardness Continuous indentation testing Macroindentation hardness Microindentations Nanoindentations Hertzian elastic behavior Plastic hardness stress–strain behavior Dislocation mechanics Ionic crystal hardness Energetic crystal hardness Indentation stress–strain behavior 

Notes

Acknowledgments

One of the co-authors, Ron Armstrong, thanks Dr. Yves Gaillard for providing both helpful reprints and information concerning his comprehensive measurements made with colleagues on nanoindenting MgO (001) crystal surfaces. Helpful correspondence has been with Dr. Munawar Chaudhri, also, in connection with Fig. 2 and with the related references [30, 31]. Publication of the present article has been supported by the UM Department of Mechanical Engineering, Center for Energetic Concepts Development (CECD).

*Notes added in proof

1. During the review period, the authors recognized that a fuller interpretation could be applied to the initial nanoindentation test results shown in Figs. 2 and 3: If the initial loading and pop-in displacements are added in each case and employed to determine dp in equation (2), then paired {(d/D), σH} values of {~0.48, ~8.7 GPa} and {~0.33, ~7.0 GPa} are respectively computed. On such basis then, the spherically-tipped nanoindentation test results are seen to follow an analogous trend to that described for the initial macroindentation test results in Fig. 1.

2. An excellent review of the history of indentation hardness testing up to the date of current reference [1] has been provided very recently in the publication: Hutchings IM (2009) The contributions of David Tabor to the science of indentation hardness. J Mater Res 24:581–589.

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Copyright information

© Society for Experimental Mechanics 2009

Authors and Affiliations

  1. 1.University of MarylandCollege ParkUSA
  2. 2.Loyola University MarylandBaltimoreUSA

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