Resistance to crazing

 

 

Principle
A specimen from the laminate under test is exposed to dry heat at 80 °C for 20 h and resistance to crazing is assessed by visual examination after cooling.

Apparatus
1. Specimen holder, suitable for holding the specimens vertically during the test and prevent contact with other specimens or the oven.
2. Electrically heated oven, provided with air circulation and capable of being maintained at (80± 2) °C.
3. Lighting, of intensity 800 to 1000 lux.
4. Conditioning chamber, in accordance with EN ISO 291, with a standard atmosphere of (23 ± 2) °C and relative humidity (50 ± 5) %.

Test specimens
The specimens shall be (250 ± 2) mm square and of the thickness of the sheet under test and shall be sanded smooth at the edges to remove any hairline cracks.
Two specimens shall be used and shall be conditioned for at least 72 h at (23 ± 2) °C and (50 ± 5) % relative humidity before testing.

Procedure
Place the specimens in the holder (see 24.2.1) and then place the holder in the oven (see 24.2.2), maintained at (80 ± 2) °C, and leave for (20 ± 1) h.
At the end of (20 ± 1) h, remove the holder and specimens and allow to cool for 3 h at ambient temperature. After the cooling period, examine the surfaces and edges with the naked eye, corrected if necessary, to determine the presence and extent of any cracking. The light intensity during the examination shall be 800 to 1000 lux.

Expression of results
The results of the examination shall be expressed in accordance with the following rating scale:
Rating 5: Surfaces and edges unchanged from ‘as received’ condition.
Rating 4: Surfaces unchanged, with slight hairline edge cracks visible to the naked eye.
Rating 3: Surface cracks visible to the naked eye, and/or moderate edge cracks.
Rating 2: Moderate surface cracks, and/or severe edge cracks.
Rating 1: Severe surface cracks, and/or delamination.
The resistance to crazing is the lower of the two results obtained from the test.