Georgia Institute of Technology Materials Science and Engineering

Committee Members:

Prof. Surya R. Kalidindi, Advisor, ME/MSE/CSE

Prof. Aaron Stebner, ME/MSE

Prof. David McDowell, ME/MSE

Prof. Richard Neu, ME/MSE

Reji John, Ph.D., Air Force Research Lab

Rapid Evaluation of Cyclic Performance Using Small-Volume Metal Samples Through Spherical Indentation

Abstract:

Cyclic testing allows the collection of basic mechanical information needed to assess a material’s response in cyclic loading. Traditionally, this information has been collected through conventional standardized cyclic tension-compression tests. The conventional testing is costly both in terms of time and money it requires.  The conventional testing methods also require large sample volumes, which may not be always available. The drawbacks of conventional test protocols become particularly evident in materials innovation efforts. This is because of the extremely high number of combinations of possible material compositions and thermo-mechanical processing histories evaluated in such efforts. More specifically, the material candidate pool is practically endless, thus, conventional testing would take an inordinate amount of time. The objective of this proposal is to develop high-throughput protocols requiring only small sample volumes to rapidly characterize the cyclic behaviors of metals. Specifically, novel spherical micro- and nanoindentation protocols will be developed and demonstrated on samples of titanium and Inconel alloys. These case studies will provide critical evaluation of the effectiveness of the new methods in capturing the differences in the cyclic responses of the different material samples. The proposed work will speed up materials design, innovation, and characterization of advanced materials. The following research questions will be addressed within this dissertation research:

1. Can microindentation and nanoindentation serve as viable high-throughput methods for rapidly assessing cyclic behaviors of metals?
2. What intrinsic material properties can be extracted from the cyclic indentation tests to effectively make comparisons across alloys?
3. Can a relationship or correlation between the results from the high-throughput cyclic indentation protocols and traditional cyclic protocols be made?

The materials tested on this work will include Ti-6Al-4V and additively manufactured Inconel 718 (AM IN718) with different process histories.

Cyclic spherical microindentation tests on the Ti64 and AM IN718 samples will be conducted to highlight the differences in cyclic behavior across the materials and the effects of the various heat treatments of AM IN718 through cyclic stress-strain loops and cyclic indentation stress-strain curves. Cyclic spherical nanoindentation tests will be performed to evaluate the cyclic behavior of specific grains of Ti64 and standard heat treated AM IN718 as well as a study on the cyclic response of the different phase morphologies of Ti64. Finally, the results from cyclic spherical microindentation will be correlated to conventional cyclic testing properties of the samples to fully develop protocols to screen for cyclic performance.