The Cyclical Exposure Test as a Tool in Laminating Quality Control

The development of cyclical exposure tests at the Puget Sound Naval Shipyard for evaluating the performance of laminated material (especially white oak) is reviewed for the period 1946-1954. Initially, a three cycle alternate soaking and drying test requiring 180 days was developed and became incorporated in a joint Army-Navy Specification known as JAN-A-397, dated 20 September, 1946. The test was performed on small beams with six white oak laminae 3/4 to 7/8-inch thick, 6 inches wide, and 48 inches long. Each cycle consisted of soaking the beams in sea water or fresh water for 30 days, then drying in summer weather or a heated room (about 80?F.) for 30 days. But 180 days was too long a period to wait for results, even on adhesive qualification tests. During other studies, details of the test were observed which led to the development of a shorter test known as the 21-day test. Even though the 21-day test was a big improvement over the 180-day test for adhesive qualifications, it was often too long for close laminating quality control. During the period when the 21-day test was being used for adhesive qualifications and other studies, it had been observed that checking on the end surfaces of white oak specimens was usually at a maximum during the fourth day of drying. By limiting drying to 3-2/3 days at slightly drier conditions, submerging the specimens prior to the first vacuum period, and eliminating the overnight soaking at atmospheric pressure, the test period was finally reduced to 12 days for three cycles. A complete description of the 12-day test equipment and methods is given.

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