Relationship of Specific Gravity to Moduli of Rupture and Elasticity in Commercial Hardboard

A total of 36 different types of commercial hardboard were studied, obtained from 11 producers in Canada and in the U.S. Five basically different processes, three thicknesses, and two classes (treated, untreated) were represented. Five 4 foot by 4 foot sheets randomly selected from each of 36 different types of hardboard were cut into 12 inch square samples. By means of random tables 12 of the 16 squares from each sheet were taken for experimental purposes, totaling 2160 specimens. Test results were analyzed for modulus of rupture, modulus of elasticity, maximum work, and work to 0.2 inch deflection. Moisture content of each test specimen was obtained after each test from samples taken closely from the area of failure. The relationship between specific gravity and flexural properties was statistically determined by regression and correlation studies. For many of the hardboards tested, relationship between specific gravity and maximum work and work to 0.2 inch deflection could not be established. General equation for the relationship between specific gravity and modulus of rupture or modulus of elasticity could not be derived. For each type of board the equation must be determined independently. The validity of established relationship holds for the specific gravity range of 0.75 – l.25. Other, types of hardboards may not have similar strength-specific gravity relationship to those considered in this study.

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