6. Apparatus
6.1 Testing Machine— A properly calibrated testing machine
that can be operated at constant rates of crosshead motion
over the range indicated, and in which the error in the load
measuring system shall not exceed 61 % of the maximum load
expected to be measured. It shall be equipped with a deflection
measuring device. The stiffness of the testing machine shall be
such that the total elastic deformation of the system does not
exceed 1 % of the total deflection of the test specimen during
testing, or appropriate corrections shall be made. The load
indicating mechanism shall be essentially free from inertial lag
at the crosshead rate used. The accuracy of the testing machine
shall be verified in accordance with Practices E4.
6.2 Loading Noses and Supports—The loading nose and
supports shall have cylindrical surfaces. The default radii of the
loading nose and supports shall be 5.0 6 0.1 mm (0.197 6
0.004 in.) unless otherwise specified in an ASTM material
specification or as agreed upon between the interested parties.
When the use of an ASTM material specification, or an agreed
upon modification, results in a change to the radii of the
loading nose and supports, the results shall be clearly identified
as being obtained from a modified version of this test method
and shall include the specification (when available) from which
the modification was specified, for example, Test Method D790
in accordance with Specification D4101.
6.2.1 Other Radii for Loading Noses and Supports—When
other than default loading noses and supports are used, in order
to avoid excessive indentation, or failure due to stress concentration
directly under the loading nose, they must comply with
the following requirements: they shall have a minimum radius
of 3.2 mm (1⁄8 in.) for all specimens. For specimens 3.2 mm or
greater in depth, the radius of the supports may be up to 1.6
times the specimen depth. They shall be this large if significant
indentation or compressive failure occurs. The arc of the
loading nose in contact with the specimen shall be sufficiently
large to prevent contact of the specimen with the sides of the
nose. The maximum radius of the loading nose shall be no
more than four times the specimen depth.
6.3 Micrometers— Suitable micrometers for measuring the
width and thickness of the test specimen to an incremental
discrimination of at least 0.025 mm (0.001 in.) should be used.
All width and thickness measurements of rigid and semirigid
plastics may be measured with a hand micrometer with ratchet.
A suitable instrument for measuring the thickness of nonrigid
test specimens shall have: a contact measuring pressure of
25 6 2.5 kPa (3.6 6 0.36 psi), a movable circular contact foot
6.35 6 0.025 mm (0.250 6 0.001 in.) in diameter and a lower
fixed anvil large enough to extend beyond the contact foot in
all directions and being parallel to the contact foot within 0.005
mm (0.002 in.) over the entire foot area. Flatness of foot and
anvil shall conform to the portion of the Calibration section of
Test Methods D5947.