AS NZS 1301.453:2016 Methods of test for pulp and paper
9 Preparation of test pieces
When testing the bending resistance in the machine direction or cross direction, the specified direction is perpendicular to the width of the test piece. Avoid folds, creases, visible cracks or other defects in the area to be tested. If watermarks are present in the test area, this shall be noted in the test report. Identify the sides of the specimens to ensure that an equal number of valid results are obtained with the force applied to each side.
Highly twisted and curled test pieces may give unreliable results. It is not possible to straighten curled or twisted samples without damaging the material.
Cut, in each required principal direction (machine direction and/or cross direction), a minimum of ten test pieces having the dimensions (38,0 ? 0,2) mm wide and at least 80 mm long (50 mm bending length).
If the shorter bending length is used, the test pieces shall be at least 40 mm long (1 0 mm bending length).
10 Procedure
If the bending resistance index (3.6) is required, determine the grammage in accordance with ISO 536.
Carry out the test with a bending length of (50,0 ? 0,1 ) mm. For samples having a bending resistance which is too low to be measured with a bending length of 50 mm, a shorter bending length of (1 0,0 ±0,1 ) mm may be used. If so, the bending length shall be reported.
IMPORTANT — The results obtained using different bending lengths will not be comparable.
Insert the test piece in the clamp, in such a manner that a given length of the test piece protrudes from the clamp and the test piece is correctly aligned. For the 50 mm bending length, this length (L) is (57 ± 3) mm; for the 1 0 mm bending length, this length (L) is (1 7 ±3) mm. Do not touch the sample in the area near the clamp with bare hands. Altering the moisture content of this area can affect the measured result.
The clamping pressure shall be high enough to hold the test piece firmly, in such a way that the measured bending force is insensitive to the pressure (see Reference [6] ).
Pneumatic or other means of ensuring that the pressure is controlled is recommended.
NOTE 1 Too high a pressure can result in lower bending-force values.
Set the instrument to a bending angle of 1 5°. Do not bend or flex the test piece in any way, prior to testing,and do not test any test piece more than once because continued flexing causes a progressive reduction of the bending force, thus causing a reduction of the bending resistance. In order to get a correct bending to a bending angle of 1 5° (or 7,5°), make sure that the knife edge is in contact with the surface of the test piece,without applying any force on the test piece prior to the testing.
If the maximum force is obtained before the test piece has been bent through 1 5°, or a break, kink or crease is observed, the test result should be discarded. If more than 1 0 % of the test pieces exhibit this behaviour, use a bending angle of 7,5°. If so, the bending angle shall be reported.