2882 



Properties 



Specific gravity, and modulus of elasticity, stress at proportional limit, 



and modulus of rupture in bending 



Tensile and compressive strengths 



Shear properties 



Stability and moisture content when water soaked 



Stability and moisture content at various relative humidities 



Chapter 23 

 Table 



23-12 

 23-13 

 23-14 

 23-15 

 23-16 



Specific gravity of these eleven hardboards appeared to be a dominant vari- 

 able only for internal bond strength; it averaged about 100 psi at a specific 

 gravity of 0.94 and increased linearly to 500 psi at a specific gravity of 1 .05 (r = 

 0.74). Within any one board type, however, specific gravity is probably corre- 

 lated with a number of mechanical properties; among board types, however, 

 factors such as tempering and wood species are dominant. 



The effect of tempering was greatest on properties related to strength of 

 surface layers (e.g., bending and tensile strength) and least on those related to 

 center layers (e.g., internal bond strength). 



Linear expansion appeared to be greater in dry-formed than in wet-formed 

 boards, suggesting that dry-formed boards may have a greater component of 

 vertical fiber orientation. 



TEMPERED 



SIS 



S2S 



DRY, SEMI- DRY 





\ "-. 



^» I 



100 



200 



300 



400 



INTERNAL BOND (PSI) 



Figure 23-1 06. — Tensile strength perpendicular to surface (internal bond strength) of Va- 

 inch-thick commercial hardboards tested at 6 to 8 percent moisture content. (Top) 

 Eleven tempered hardboards. (Bottom) Three standard hardboards. See table 23-11 

 for descriptions of boards tested. (Drawing from Suchsland and Woodson 1985, 

 based on data from Werren and McNatt 1975, text footnote 5.) 



