7.4.1.1 Preparation of specimens 7.4.1.1.1 Long sheets
Twenty specimens are required. The specimens shall be longitudinally cut from the middle of a complete sheet, with two complete corrugations or, if the sheet is not wide enough, one complete corrugation.
Specimens may be transversely cut to a length allowing a clear span of 12 times the height of corrugation.
The specimens shall be longitudinally cut in the valley a little beyond the axis, as indicated in
!Figure A.17". 7.4.1.1.2 Short sheets
Twenty specimens are required and prepared as for the bending moment test described in 7.3.2.2.1.
7.4.1.2 Apparatus
7.4.1.2.1 Freezer having a forced air circulation and capable of being regulated to the prescribed freezing conditions with a full load of specimens.
7.4.1.2.2 Bending test machine as specified in either 7.3.2.1.2 for long sheets or 7.3.2.2.2 for short sheets.
7.4.1.2.3 Water bath filled with water and maintained at (20 ± 4) °C.
7.4.1.3 Procedure
Divide the specimens at random into two lots of 10.
Submit the first lot of ten specimens to the breaking load test, in 7.3.2.1 for long sheets (taking for w the average of two measurements of the width of the specimen), or to the bending moment test, in 7.3.2.2 for short sheets, including the conditioning procedure (see Table 8).
At the same time, immerse the second lot of specimens in water at ambient temperature (> 5 °C) for 48 h.
Then subject the second lot of specimens to 100 of the following freeze-thaw cycles:
— cool (freeze) in the freezer which shall reach a temperature of (-20 ± 4) °C within 1 h to 2 h and hold this temperature for a further 1 h;
— heat (thaw) in the water bath which shall reach a temperature of (20 ± 4) °C within 1 h to 2 h and hold at this temperature for a further 1 h.
During both the cooling and heating (freezing and thawing) cycles, position the specimens to enable free circulation of the conducting medium (air in the freezer or water in the bath) around them.
Each freeze-thaw cycle shall take between 4 h and 6 h but an interval of 72 h maximum may be taken between cycles during which the specimens shall be stored in water at 20 °C.
Control of the freeze-thaw cycles can be automatic or manual. Continuous automatic cycling is preferable. For manual control, record the completion of each cycle.
Carry out the breaking load test in 7.3.2.1 for long sheets (taking for w the average of two measurements of the width of the specimen) and the bending moment test in 7.3.2.2 for short sheets, including the conditioning procedure (see Table 8).
7.4.1.4 Expression and interpretation of results
For each of the two lots, calculate the mean breaking load or bending moment and the standard deviation at the value obtained.
Let X1 and s1 be the mean and the standard deviation of the results obtained on the first lot, and X2 and s2 be the mean and the standard deviation of the results obtained on the second lot tested after freeze- thaw cycles.
Calculate (ISO 2602):
— L2 = X2 - (0,58 x s2) which is the lower estimation of the mean breaking load or bending moment after freeze-thaw cycles at 95 % confidence level (second lot);
— L1 = X1 + (0,58 x s1) which is the upper estimation of the mean breaking load or bending moment at 95 % confidence level of the reference lot (first lot).
Calculate the ratio, RL, as follows:
L L
R =L2
1
The result shall conform to 5.4.2.
7.4.2 Heat-rain
7.4.2.1 Preparation of specimens
The specimens shall comprise a minimum of one full sized sheet with the underlapping and overlapping sheets/strips surrounding it a minimum of ẵ sized sheets. Twelve specimens are required for sheets of length equal to or less than 0,9 m or nine specimens for longer sheets.
7.4.2.2 Apparatus
7.4.2.2.1 Frame with dimensions capable of taking at least one full size sheet and the overlapping strips, inclined at (25 ± 5)°, placed in a ventilated area.
7.4.2.2.2 Heating device capable of maintaining the specified uniform temperature on the surface of the tested elements, at the crowns of the corrugations.
The heating device shall have a power output regulated by means of a black body temperature sensor located at the central area of the test rig where the maximum temperature is expected, i.e. at the closest distance underneath a heating unit.
The temperature at this location shall be regulated at (70 ± 5) °C and shall be reached after 15 min of heating.
At any time the difference between black body temperature in the centre and black body temperature near the corners of the test rig, also measured underneath heating units and at the crowns of the corrugations, shall not exceed 15 °C.
7.4.2.2.3 Water sprinkling device with an output of approximately 2,5 l/(m2.min), delivering water of ambient temperature (> 5 °C).
NOTE For this test, an aluminium plate of 1 mm thickness painted with a matt black paint is used as a black body, the measurement device being a thermocouple or a similar device fixed on the surface of the aluminium plate.
7.4.2.3 Procedure
Condition the specimens by storing them to allow them to reach equilibrium for 7 days in a laboratory atmosphere.
The number of full size sheets will depend on the size of the frame but shall be at least one.
Lay each sheet with overlaps at the four edges. At the edges of the frame, overlaps can be provided by strips of sheets.
Fix the specimens on the frame according to regulations or, if no regulations exist, to manufacturer’s instructions. One installation system, which the manufacturer regards as decisive for the sheets, shall be selected.
Submit the upper face of the sheets to 50 cycles without interruption in accordance with Table 9.
Table 9 — Heat-rain cycle
Cycles Duration
Wetting 2,5 l/( m2.min) 2 h 50 min
Pause 10 min
Heating (70 ± 5) °C 2 h 50 min
Pause 10 min
Total cycle 6 h
After 50 cycles, inspect the sheets for the following:
— cracking (longitudinal, transverse and at the fixing points);
— delamination;
— other visible defects.
7.4.2.4 Expression and interpretation of results The results of the visual assessment shall conform to 5.4.3.
7.4.3 Freeze-thaw test for fittings
The specimens shall be cut from complete fittings and shall be at least 200 mm x 200 mm.
The apparatus is the same as for sheets.
Five specimens cut from different fittings are submitted to the same freeze-thaw cycle as sheets.
After the 100 cycles are completed, examine them with the naked eye for cracks, delamination or other defects and record any observations. These observations shall conform to 5.4.2.