Structural Flakeboards and Composites 3009 



24-14 CREEP" 



When wood-based panels are loaded in bending, an immediate deflection 

 occurs; this deflection increases with time, and the increase is called creep. 

 Price'^ provided data specific to southern pine plywood, and flakeboards made 

 of mixed species of southern woods according to the optimum procedures of 

 Hse et al. (1975) as summarized in footnote 1 of table 24-12. 



The oriented- strand flakeboards were made in 4- by 8-foot size at the Potlatch 

 Corporation pilot plant in Lewiston, Idaho; the boards with random flake orien- 

 tation were fabricated in 4- by 8-foot size at the pilot plant (20-foot, top-closing 

 press) of the U.S. Forest Products Laboratory at Madison, Wis. Press closing 

 speeds and platen pressures differed at the two pilot plants, as did the phenolic 

 resin recipe, so surface densification profiles and bonding characteristics dif- 

 fered with pilot plant. Plywood for the study was three-ply southern pine CDX 

 sheathing purchased in central Louisiana. Price's study included both 1/2- and 5/ 

 8-inch-thick panels, but for brevity only his data on 1/2-inch panels are present- 

 ed here. 



Loads were applied to panel specimens (fig. 24-46A) for 32 days, followed by 

 8 days with loads removed; during this 40 days, deflections were recorded as 

 relative humidity (RH) in the test chamber was alternated from 50 to 85 percent 

 at regular intervals in 4-, 8-, and 32-day cycles. On the 8-day cycle, for exam- 

 ple, specimens were first held at 50 percent RH for 4 days, then at 85 percent RH 

 for 4 days, and then returned to 50 percent RH for 4 days, and so on. 



Specimens were loaded in two modes and at two load levels, as follows: 



• Flexural specimens, which measured 18 inches long and 3 inches wide, 

 were center-point loaded in bending (fig. 24-46A top) over a 15-inch 

 span to yield bending stresses of 300 and 450 psi on specimens cut to 

 represent the 4-foot panel direction, and 450 and 600 psi on those cut to 

 represent the 8-foot direction. 



• Concentrated loads, 200 pounds applied on a 1 -inch-diameter disk and 

 300 pounds applied on a 3-inch disk (fig. 24-46 A bottom), were located 

 2-1/2 inches from panel edge at midpoint of a 16-inch span; face-veneer 

 grain and oriented strands of panels were arranged parallel to the span. 



Mechanical properties of the 1/2-inch-thick panels evaluated by 

 Price'^ were as follows: 



'^ext under this heading is condensed from: Price, E. W. 1982. Effect of time, load, and 

 environment on ten designs of structural flakeboard composed of southern species. U.S. Dep. 

 Agric, For. Serv., South. For. Exp. Stn., Alexandria, La., Fin. Rep. FS-SO-3201-3. 16. 



