6533b837fe1ef96bd12a3052

RESEARCH PRODUCT

Improving surface detection on nanoindentation of compliant materials

subject

description

Nanoindentation is a versatile tool for monitoring mechanical properties on a local scale. Accurate knowledge of a contact area, and therefore an initial contact, is however necessary for translating the force curve into sample mechanical properties. It is shown that methods for sensing an initial contact by depth sensing instruments (DSI) may be severely in error for compliant materials. With the hardware adopted in this work, the threshold is determined by the elastic modulus; hence the error potentially increases if the material becomes more compliant. A simple method is therefore suggested to determine with accuracy the initial contact on compliant materials whereby the surface contact can improve, with respect to standard procedures, by several tens of nanometers for moduli in the range of 108 Pa up to the order of micrometers for moduli of the order of 106 Pa using a spherical tip of radius 0.075 mm. Assuming that this position represents the real surface, a comparison with the depth, necessary to give rise to surface detection with a finite threshold with the Hertz approach, shows significant deviations. Possible causes reside in experimental limitations as well as compliant materials' mechanical behaviour.