A-A-549D
(2). Creep Test. Sufficient amount of 13.3 + 0.64 x 13.3 + 0.64 cm (5 + 1/4” x 5 + 1/4”) squares of cushioning material to make a stack not less than 5 cm (2.0) high shall be cut from randomly selected areas of each sample unit in a manner which will provide the maximum number of closed air cells. The cushioning material shall be interleaved with pieces of pressboard 0.61-0.91 mm (0.024”-0.036”) thick and approximately 13.8 x 13.8 cm (5-1/2” x 5-1/2”) in size. The squares of cushioning material shall be arranged so that each cell is directly over the corresponding cell in the square below. This stack of cushioning material interleaved with pressboard shall be placed on a rigid horizontal platform not less than 15 x 15 cm (6” x 6”). An adjustable weight with an even, level, rigid, bottom surface measuring approximately 14 x 14 cm (5-1/2” x 5-1/2”) shall be centered on the stack so that the bottom of the weight is in contact with the top of the stack. The weight shall be adjusted to provide pressure of 0.62 to 0.76 kPa (0.09 to 0.11 psi) on the cushioning material. After 60 + 5 minutes, the vertical distance between the bottom surface of the weight and the horizontal platform shall be measured at each of the 4 corners of the stack with an instrument capable of measuring 0.25 mm (0.01”). The measurements shall be taken carefully so as not to disturb the stack. These 4 measurements shall be averaged to determine the initial stack height. The initial stack height, minus the total thickness of the interleaving sheets, divided by the number of pieces of cushioning material in the stack, yields the initial thickness or the cell height. The weight shall be kept on the stack for a total of 168 + 2 hours, then the distance between the bottom surface of the weight and the horizontal platform shall be measured again and the final thickness determined in the same manner as the initial thickness. The final thickness shall be not less than 80% of the initial thickness.
(3). Deflation Test. A specimen containing at least 100 cells shall be cut from each sample unit and examined for deflated cells. Any deflated cells found shall be marked. Not more than 5 percent of the cells shall be deflated. If no more than 5 percent deflated cells are found, the specimen shall be placed in a vacuum vessel and the vessel evacuated to a pressure of 45.7 + 2.5 cm (18 + 1”) of mercury for 5 minutes. The pressure shall then be returned to ambient and the test specimen examined for unmarked cells which were deflated by the reduced pressure. Not more than 10 % of the unmarked cells shall be deflated.
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