10.5 Measurement
Procedures
10.5.1 Bending Strength
The fracture strength measured during a
bending test depends on many factors such as the dimensions,
cross sectional geometry, surface quality, loading velocity,
environmental humidity, the geometry of the test device and
the procedure. The result of such a test gives an indication
of the general magnitude of the strength properties
of the material, but cannot be directly used
as design data. It is suitable for quality-control
and for the general comparison with various materials, provided
all of the parameters mentioned above remain constant. In
practice, both 3-point and 4-point bending tests are used.
The necessary test equipment consists of:
- a mechanical test machine, with which a test piece is
loaded with constant rate of force increase and which is
capable of measuring the peak stress with an accuracy of
± 1 %,
- a test piece loading jig whose geometry and dimensions
are suitable for the test,
- a micrometer meeting the specifications of ISO 3 611
and capable of measuring test piece dimensions to an accuracy
of ± 0.01 mm,
- a travelling microscope with a slide rule or similar
measuring device meeting the specifications of ISO 6 906
in order to measure the distance between the centre axes
of the sample supports and the loading pins.
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