Measurement of Mechanical Properties at High Strain Rates by Nanoindentation

High strain rate nanomechanical testing has the potential to expand the frontiers of materials science with high-throughput investigations of dynamic nanoscale mechanical phenomena at strain rates commensurate with those in the ballistic range. Recent advances in electronics have ushered in an exciting new era that has led to the development of new instrumentation and testing methods that can perform incredibly fast nanoscale mechanical tests (< 200 µs). However, due to the inherent dynamic nature of these short-lived tests, it is critical to have a deep understanding of the testing system’s dynamics to ensure accurate measurements. To this end, a novel nanoindentation system with a laser interferometer that tracks the indenter’s movement at a sampling rate of 1.25 MHz is described. Conversion of this displacement data into load by use of Newton’s laws allows for synchronous load and depth measurements at indentation strain rates up to 10^4/s, from which high strain rate mechanical properties such as the hardness can be deduced. In this presentation, we address hardware and analysis challenges associated with high strain rate nanoindentation and explore the limits of the accessible strain rate range.