Niget: NanoIndentation General Evaluation Tool

6 Oliver Pharr with ODR

For a definition of the Oliver Pharr method see [11].
This method is shown unless the software was compiled using the NOFORTRAN option.

Figure 6: Oliver-Pharr analysis using orthogonal data regression

6.1 Window

The window consists of several blocks:

  • Info displays the maximum depth and force during the indentation

  • Parameters shows the selected range in nm and in % of the maximum force, the correction β and the fit button.

    • -

      The fitting range can be selected either using the mouse or typing in the range entries. The range can be defined either in nm or in percent of the maximum force. It is often recommended to use the range 40 - 98 % Fmax for the fit, see section 6.2.

    • -

      The parameter β accounts for any deviations from the axisymmetric case and is used in the calculation of the reduced modulus in equation (10). Currently, the default value is no correction β=1.0. The value supplied by the user is saved in the settings and can be reset to its default value.

    • -

      fit button, see section 6.2 for details of the calculation

  • Results displays all results in the following order: the residual depth hp, the power m of the power law function, the parameter ε, the contact depth hc, the slope S, the contact area Ap(hc), the indentation hardness HIT, the contact modulus Er, the indentation modulus EIT and the ranges used for the fitting procedure. The variables are described in detail in section 6.2. If the fittings procedure failed a warning is shown.

  • Uncertainties show the uncertainty analysis window, see section 14.2.1.

  • Show log Show the report about the fitting procedure in a separate window. The reports are saved to files fit.log.op.err and fit.log.op.rpt.

  • Save save parameters and results to given file.

  • Graph display the unloading curve and the fitted curves. Stepwise zooming/unzooming can be performed by selecting a range with the mouse and pressing the Zoom/ Unzoom buttons. The graph is restored to its original size by the Restore button.

6.2 Procedure

This is a slight modification of the standard Oliver Pharr method described in section 5.2 using a better fitting procedure.

  1. 1.

    Fit the upper part of the unloading curve with a power law function

    F=α(h-hp)m.

    using orthogonal least squares as implemented in the package ODRPACK95 [13]. The range should be approx. 40 - 98 % Fmax. All three parameters are fitted.

  2. 2.

    same as steps No. 3-4 in 5.2.