Dynamic Viscoelasticity in Hardboard

Two types of hardboard composed of the same kind of fibers but made differently were tested by means of nondestructive dynamic vibrations. The data obtained were analyzed using relations utilized in the vibrating reed experiment. The viscoelasticity of both hardboards were plotted and the effect of moisture content and the technique of manufacture on the viscoelastic behavior was discussed. A comparison between the dynamic and static moduli of elasticity was finally made for the two boards over the experimental moisture content. The results obtained in this investigation confirm the viscoelastic nature of hardboard. Using the vibrating reed method many viscoelastic parameters for hardboard can be determined. Moisture content, as expected, did affect the vibrational characteristics of both wet- and dry-processed hardboards. The viscoelastic losses were maximum at the upper end of the moisture content scale. The differences in the viscoelastic nature of the two types of hardboard used were not sizable although the dry-processed board exhibited superior elasticity. These differences were less when the data were adjusted to account for the density and equilibrium moisture content differences that existed between the dry- and wet-processed boards. The results of this study open a possibility for more effective hardboard testing and quality control.

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