Structural Flakeboards and Composites 



20 



2961 



30 60 90 



ANGLE OF FLAKE GRAIN TO LOAD (DEGREES) 



60 90 



ANGLE OF FLAKE GRAIN TO LOAD (DEGREES) 



Figure 24-29. — (Left) Relationship between MOE and orientation of flakes in tensile 

 specimens cut from 42-pound, 1/2-inch flakeboard of sweetgum veneer flakes 0.015- 

 inch-thick, 3 inches long, and 3/8-inch wide. Resin content 5 percent. (Right) Relation- 

 ship between ultimate tensile strength and orientation of flakes in tensile specimens 

 cut from this flakeboard. (Drawing after Price 1974.) 



1/2-inch sweetgum board couM be very substantially increased by aligning 

 flakes so that their grain angle was within 15° of alignment with direction of load 

 application. With perfectly formed, 0.015-inch-thick, 3-inch-long flakes per- 

 fectly aligned with the direction of tension loading, it was possible to obtain an 

 MOE of over 1 ,800,000 psi and an ultimate tensile strength of over 8,000 psi 

 (fig. 24-29). These values were attained at a panel density of only 42 Ib/cu ft. 



The flakes used by Price were cut from 0.015-inch-thick veneer to precise 

 length (3 inches) and then clipped to precise width (3/8-inch) to yield extremely 

 uniform flakes (fig. 18-264). In subsequent discussion these perfect flakes will 

 be termed veneer flakes. 



In another comparison of MOE of panels with aligned flakes and random 

 flakes. Price (1978) used mixed-species flakes cut on a shaping lathe (fig. 18- 

 274abc) — hereafter referred to as lathe flakes — and found alignment yielded an 

 MOE of about 1 million psi along the major panel axis, whereas panels with 

 random flakes averaged about two-thirds that value (table 24-12). 



Wood density and species. — Hse (1975c) made panels 0.5 inch thick from 3- 

 inch-long, 0.015-inch-thick, 3/8-inch-wide veneer flakes of nine species of 

 hardwoods commonly found on southern pine sites. He found that the main 

 effects of species were related to variation in wood density. Low-density species 

 compacted readily when pressed, and the resulting good flake contact improved 

 bonding and gave boards of high strength. With species having specific gravity 

 above 0.6, it was difficult to form stiff boards without increasing panel density 

 unduly (table 24-11). 



The typically cross-grained flakes of black tupelo yielded panels of exception- 

 ally low MOE, even though wood specific gravity was below 0.6. Sweetbay 

 yielded flakeboards with highest MOE. Only minor differences in MOE were 

 noticed among sweetgum, red maple, white ash, hickory, and southern red oak. 

 Both post oak and white oak yielded flakeboards of substantially lower MOE. 



