Dr. Warren C. Oliver, president of Nanomechanics Inc., has co-authored a paper published in a special “Advanced Nanoindentation in Materials” edition of Materials.
Written with Nanomechanics Inc. scientist Sudharshan Phani Pardhasaradhi, the article, is entitled “Ultra High Strain Rate Nanoindentation Testing.”1
From the abstract:
Strain rate dependence of indentation hardness has been widely used to study time-dependent plasticity. However, the currently available techniques limit the range of strain rates that can be achieved during indentation testing.
Recent advances in electronics have enabled nanomechanical measurements with very low noise levels (sub nanometer) at fast time constants (20 µs) and high data acquisition rates (100 KHz). These capabilities open the doors for a wide range of ultra-fast nanomechanical testing, for instance, indentation testing at very high strain rates.
With an accurate dynamic model and an instrument with fast time constants, step load tests can be performed which enable access to indentation strain rates approaching ballistic levels (i.e., 4000 1/s). A novel indentation based testing technique involving a combination of step load and constant load and hold tests that enables measurement of strain rate dependence of hardness spanning over seven orders of magnitude in strain rate is presented.
A simple analysis is used to calculate the equivalent uniaxial response from indentation data and compared to the conventional uniaxial data for commercial purity aluminum. Excellent agreement is found between the indentation and uniaxial data over several orders of magnitude of strain rate.
Co-developer of the Oliver-Pharr method, Oliver obtained his Bachelor of Science degree in Materials Science from the University of Tennessee in 1976. He received a Master of Science and Ph.D. of Materials Science in 1981 from Stanford University studying with Professor W. D. Nix. In 2009, he helped form and became president of Nanomechanics, Inc.
During the course of his research career, Dr. Oliver has made notable contributions to the area of intermetallic alloy development and the mechanical characterization of materials and structures on the micro- and nanoscale. In particular, he has contributed to the development and commercialization of nanoindentation/nanoindenter equipment and techniques.
1Sudharshan Phani, P.; Oliver, W.C. Ultra High Strain Rate Nanoindentation Testing. Materials 2017, 10, 663.