Scratch Hardness Test Using a Diamond Stylus on

the Micro-Tribometer mod. UMT-2

ASTM G171-03


Summary of Test Method:


This test method is used to determine the scratch hardness number of the surfaces of solid materials. The test involves producing a scratch by moving a diamond stylus along a specified path under a constant normal force and with a constant speed. The average width of the scratch is measured on a separate instrument. The scratch hardness number is computed as follows; the applied force is divided by the scratch width and the result is multiplied by a geometrical constant

The UMT maintains a constant normal force with its servo-controlled system. An x-axis slider moves the diamond stylus across the test specimen to produce the scratch. The friction/load sensor also measures the tangential scratching force for computing the stylus drag coefficient.


Test Parameters



Applied Load

Stroke Length




200 g *

5 mm minimum

0.2 to 5.0 mm/s


        The applied load may vary depending on the material being tested. It must be sufficient to produce a measurable and repeatable scratch.


The diamond stylus is conical with an apex angle of 120 and a hemispherical tip radius of 200 m.


The UMT allows for monitoring during the test the actual dynamic normal force, scratching force and drag coefficient, and depth of scratch. Additionally, the acoustic emissions produced during the test may be recorded.

UMT Hardware Configuration:


         4 Mounting Block PN M30C116

         Model DFM-0.5 Dual Friction/Load Sensor

-          range 5 to 500 g

         Suspension PN AM30B825-1

         Pin Holder - PN AM30B534

-          for sensors mod. DFM

         Diamond Tip Indenter Class A, B

         Test Specimen

         Stationary Specimen Table

         Optional Additional Sensor

- mod. AE-5 Contact Acoustic Emission Detector








UMT Software Test Setup:


UMT Options File:

Load the options file that contains settings for 500 g force/load sensor.


Test Sequence:

The Test Sequence should consist of 2 sheets.


Sheet 1 is for settling time for the carriage to establish the initial normal load.

Carriage - applies a 200 g Constant Force for a Duration of 10 sec.

Spindle Velocity is 0 revs/min.

Slider is idle.

Sheet 2 is for the actual scratch test.

Carriage - applies a 200 g Constant Force for a Duration of 30 sec.

Spindle Velocity is 0 revs/min.

Slider Velocity is 0.33 mm/sec., Increment Offset is 10 mm, and Direction is left.


Data Collection:

The following should be checked under DataFile:

Fx Friction Force

Fz Normal Force

T Time

Z1 Carriage Position (Used to determine Wear Depth)

Z3 Slider Position




Use the Viewer program to plot test results.

Select the parameters to be displayed by checking the appropriate box under Parameters on the Viewer screen. For viewing stylus drag coefficient plots click on the COF box.