How a Nanoindenter Works
The factors involved in mechanical testing are load, displacement, area and time. Load (P) is the force exerted on sample. Displacement (h) is the distance the indenter travels into a material. Area (A) is a measure of the interaction of the indenter in contact with the sample.
Schematic of an indentation test
Nanoindentation is typically conducted with a calibrated Berkovic diamond indenter tip. A Berkovich tip is a three-sided pyramidal indenter. The three sides allow the tip to be theoretically sharpened to an atomic point.
During the nanoindentation process, a calibrated indenter tip approaches the surface of the sample. The force-displacement data is used to determine the point of contact. After the sample is contacted, the force is linearly increased and the tip indents into the surface of the sample. A short dwell time occurs at the maximum force and then the sample is unloaded. At the initial point of unload, the stiffness is measured.
The resulting load and displacement data along with the area from the calibrated indenter tip allows for the determination of mechanical properties such as elastic modulus and hardness.
Nanoindentation in nickel
A more complete technical discussion of indentation based on the Oliver-Pharr method is in this review: Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology.