'ZERO POINT' IN THE EVALUATION OF MARTENS HARDNESS UNCERTAINTY
Abstract
The Instrumented Indentation Test is based on simultaneous recording of force and indentation depth, obtained during test cycle. The force-depth curve, describing the indentation pattern, is typically formed by two parts having the “zero-point” in common, i.e. the first contact point between the indenter and the surface of test piece. The zero-point determination is a crucial aspect for Martens Hardness evaluation, so that relevant ISO standard suggests to estimate it by extrapolation of polynomial fitted functions. In this paper a new model, based on a segmented function, is proposed. This approach implies the use of maximum likelihood estimator for parameters determination. The corresponding uncertainty is provided through the covariance matrix of the regression model.
Event details
- Event
- Joint International Conference on Force, Mass, Torque, Hardness and Civil Engineering Metrology in the age of globalization
- Technical Committee
- TC5
- Place
- Celle, GERMANY
- Time
- 24 September 2002 - 26 September 2002