Because of its ease of implementation and insensitivity to indenter drift, dynamic indentation techniques have been frequently used to measure mechanical properties of bulk and thin film materials as a function of indenter displacement. However, the actual effect of the oscillating tip on the material response has not been examined. Recently, it has been shown that the oscillation used with dynamic indentation techniques alters the measured hardness value of ductile metallic materials, especially at depths less than 200 nm. The alteration in the hardness is due to the added energy associated with the oscillation which assists dislocation nucleation. Atomistic simulations on nickel thin films agree with experiments that more dislocations are nucleated during dynamic indents than with quasi-static indents. Through the analysis of quasi-static and dynamic indents made into nickel single crystals and thin films, a theory to describe this phenomenon is presented. This is coined the Nano-Jackhammer effect, a combination of dislocation nucleation and strain rate sensitivity caused by indentation with a superimposed dynamic oscillation.
Bibliographical noteFunding Information:
We would like to thank J. Houston of Sandia National Laboratories, Albuquerque, New Mexico, for his thorough reading of the manuscript and, particularly, for his original insightful understanding and suggestion of the Nano-Jackhammer effect. Film deposition at the University of Minnesota was supported by the NSF MRSEC. The simulations were performed using Virginia Tech’s supercomputer system X and the code LAMMPS, provided by S. Plimpton, Sandia National Laboratory. Research support through NSF Grant CMS 03224361 and the United States Department of Energy Office of Science Grant DE-AC04-94AL8500 are gratefully acknowledged.
Copyright 2009 Elsevier B.V., All rights reserved.
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- Dynamic fracture
- Mechanical testing
- Numerical algorithms