PPP-C-1120D
4.5 Tests.
4.5.1 Compression set. The test specimens shall be 6 ±⅛-inch square with a minimum thickness of two inches. If the specimen is less than 2 inches thick, multiple layers shall be used. The thickness of each specimen shall be measured prior to preworking. Preworking shall consist of compressing the specimen between parallel rigid plates to 65 percent of its thickness. Compress a total of 10 times at a rate of approximately three times per minute. The specimens shall be allowed to recover a minimum of 4 hours after the final compression. The specimen shall then be loaded as follows: 20 pounds for type II, 30 pounds for type III, 55 pounds for type IV. The load shall be applied to the specimen evenly and gently. Three minutes after
application, the load shall be removed. One minute after the load has been removed, the thickness of the specimen shall be redetermined. Specimen compression set is the difference between the preworked and final thickness expressed as a percent and calculated as follows:
Percentage compression set = (tP - tf) x 100/tp) Where: tp = preworked thickness
tf = final thickness
Five specimens shall be tested and the average compression set determined.
4.5.2 Dynamic compression resistance. A dynamic compression resistance test machine shall be used. The test machine shall consist of an instrumented, weighted drop platen and an impact base with dimensions which are at least 1 inch larger than the corresponding specimen dimensions. The weighted drop platen shall fall freely upon release onto the specimen which is supported by the impact base. The impact base shall be rigidly supported by a massive unyielding foundation. The drop platen, impact base, and supporting foundation shall be free of disturbing mechanical resonances over the frequency range 0-500 Hz. The test machine and
instrumentation shall be capable of measuring the drop platen acceleration pulse generated by the cushioning specimen with an accuracy of ±5 percent. The test specimen shall be an 8 by 8 inch rectangular solid, 4 inches thick, made from plies of one sample unit, if necessary. The drop platen loaded to the specified static bearing stress shall be dropped from a height of 24 inches.
At impact, drop platen, impact base, and specimen bearing surfaces shall be centered and
parallel. Five drops with a 1 to 2 minute recovery interval between drops shall be made on each specimen at the static bearing stress specified in table I. Testing shall proceed in the order of increasing static bearing stress until either the test is completed or until 10 percent compression set is incurred by the specimen. When 10 percent compression set is incurred by a specimen, it shall be replaced by an untested specimen made from the same sample unit as the replaced specimen. For each static bearing stress, the five peak accelerations shall be averaged and reported as the specimen peak acceleration. The above series of tests shall be conducted on five test specimens. The second through fifth specimen peak accelerations shall be averaged for each specified static bearing stress. Average peak accelerations exceeding the limits specified in
table I shall be cause for rejection of the lot.
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