Structural Flakeboards and Composites 2983 



flakes were aligned at board density of 45.5 Ib/cu ft, and 83 psi with random 

 flake placement at a board density of 47.5 Ib/cu ft (fig. 24-38 bottom). 



Price (1978) fabricated 4- by 8-foot mixed-species flakeboard panels with 

 aligned faces and cores, and also with random flake placement, using proce- 

 dures (see table 24-12) similar to the optimum suggested by Hse et al. (1975). 

 He found that to obtain an IB of 70 psi, 1/2-inch-thick panels must exceed 43 lb/ 

 cu ft and 5/8-inch panels 47 Ib/cu ft in density. As exposure induced weathering 

 or as moisture increased, IB decreased (table 24-17). Increasing RH from 50 to 

 65 percent decreased IB an average of 7.6 psi because of moisture increase or 

 density decrease or both. Modified aging and accelerated aging reduced IB 

 strength drastically. The average modified aging strength (13.5 psi) was only 21 

 percent of the 65 percent RH average. Accelerated aging reduced the IB an 

 additional 8 percent. For the mixed-species panels, only 10 percent of the 65 

 percent RH strength was retained after accelerated aging, but the single-species 

 panels — which were made of low-density woods — retained 28 percent. 



PLATE SHEAR STRENGTH 



Price (1978) evaluated the plate shear strength of 17.5-inch-square specimens 

 cut from the 4- by 8-foot panels described in the preceding paragraph and in table 

 24-17. These specimens were tested according to ASTM D 3044-72 of Ameri- 

 can Society for Testing and Materials (1976). This property is important when 

 flakeboards are used as webs in I-beams or boxbeams — as they likely will be in 

 fabricated joists of various designs. 



Price found that at a density of 46 Ib/cu ft, the shear modulus of the random 

 panels (259,000 psi) was 35 percent higher than that of the oriented panels 

 (192,000 psi). The regression slopes of panel density on shear modulus were 

 statistically equivalent for both 5/8-inch panels and the 1/2-inch random panel 

 (table 24-18). Since the slope applicable to the 1/2-inch oriented panel was not 

 the same as that for the 1/2-inch random panel, at higher or lower densities, the 

 35-percent difference in shear modulus will not be maintained. 



IMPACT STRENGTH 



Structural panels for use as sheathing or decking in building construction must 

 have acceptable impact strength to withstand loads imposed when offloading 

 panels at the building site, during construction, and during use. Impact loads are 

 probably most severe during construction when building materials or tools are 

 dropped, or when carpenters jump from level to level. 



Johnson and Haygreen's (1974) evaluation of the impact behavior of aspen, 

 Douglas-fir, and southern pine phenolic-bonded and urea-bonded structural 

 particleboards in comparison with Douglas-fir plywood will likely be of interest 

 to readers needing background information. Readers needing a review of meth- 

 ods to evaluate impact behavior of sheathing material should refer to Superfesky 

 (1975). 



