6. Apparatus
6.1 Testing Machines:
6.1.1 There are two general types of machines available for
making this test. One type is a self-contained unit built for this
purpose, and the other type is an accessory available to existing
microscopes. Usually, this second type is fitted on an invertedstage
microscope. Good descriptions of the various machines
are available.3,4
6.1.2 Design of the machine should be such that the loading
rate, dwell time, and applied load can be standardized within
the limits set forth in 3.1.1. It is an advantage to eliminate the
human element whenever possible by appropriate machine
design. The machine should be designed so that vibrations
induced at the beginning of a test will be damped out by the
time the indenter touches the sample.
6.1.3 The calibration of the balance beam should be checked
monthly or as needed. Indentations in standard glasses are also
used to check calibration when needed.
6.2 Indenter:
6.2.1 The indenter shall meet the specifications for Knoop
indenters.3 See Test Method E 384.
6.2.2 Fig. 1 shows the indenter and its maximum usable
dimensions. The diagonals have an approximate ratio of 7:1,
and the depth of the indentation is about 1⁄30 the length of the
long diagonal. A perfect Knoop indenter has the following
angles:
6.2.2.1 Included longitudinal angle 172° 30 min 00 s.
6.2.2.2 Included transverse angle 130° 00 min 00 s.
6.2.3 The constant Cp for a perfect indenter is 0.070 28, and
the specifications require a variation of not more than 1 % from
this value.
6.3 Measuring Microscope—The measurement system shall