Effects of Three Cyclic Constant Levels of Moisture Content on Creep Deflection in Hardboard

Wet process and dry process hardboards (density about 1 gm/cm3) were made in the laboratory using the same fiber source. Twenty panels, 17 inches by 17 inches by 0.25 inches in size, were produced, half by dry and half by, wet process. Bending specimens measuring 12 inches by 2 inches were subsequently cut from these panels for testing in flexural creep. In all, 78 creep specimens were involved which were equally divided between wet and dry process boards. These specimens were then conditioned and tested at nominal constant moisture contents of 2, 8, 18, 8, 2, 8, 18, 8, 2, 8, 18, 8, and 2 percent. At each of these conditioning stages, three wet process and three dry process specimens were tested. The actual moisture content, after equalization, at the above stages were 0.77, 5.10, 16.81, 6.99, 0.91, 7.27, 18.77, 7.56, 0.92, 6.86, 18.79, 7.45, and 0.94 percent for the wet process boards. The actual moisture contents of the dry process boards were only slightly different than those just noted. The test consisted of 3-point flexural loading with mid-span deflection data monitored over a 4-hour period. During the first 2 hours the load (10 pounds) was applied. The recovery period, was monitored during the second 2-hour period. The deflection data were statistically analyzed at all 13 moisture levels in terms of instantaneous elastic, retarded elastic, and flow components. Time effects were generally smaller for the wet process samples particularly during the first eight moisture stages. Over the last four stages, however, the behavior of the two types of boards were similar.

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