Alignment uncertainties in ideal indentation styli

In this work, the first and second order uncertainty contributors in depth-sensing hardness measurements are investigated. Each term in the hardness expanded uncertainty is examined to determine the typical sources and the magnitude errors contributed to the measurement. In particular, using simulations based on ideal indenter geometries the depth uncertainty with area function uncertainty due to rotational misalignments between the stylus and the specimen is evaluated. Three typical styli are simulated; standard Berkovich, modified Berkovich, and Vickers geometries. Considering the maximum allowable tip and tilt from ISO 14577, the area function uncertainty was less than 1%. Also considered is the effect of the twist about the central axis which shows that, because of the asymmetric shape, the Berkovich geometries have larger errors as a function of rotational deviations than the Vickers geometry from a perfect alignment.