Correlation Between Internal Bond and the Shear Strength Measured By Twisting Thin Plates of Particleboard

Shear strength of nine thin commercial particleboards (3/16 to 3/8 inch) was measured by twisting plate specimens of various sizes. Because of the thickness variation shear values were obtained from the maximum torque through the conversion of St. Venant’s equation. It was found that the apparent shear strength was affected by specimen size and also by particle orientation. The 2- by 8-inch (6-inch gauge length) specimen appeared to be the most suitable size for twisting-shear method for board thicknesses in the range 3/16 to 3/8 inch. A very close correlation was found between the shear strength and internal bond strength measured by the conventional tension-perpendicular method for those nine boards. Both twisting-shear and internal bond failures were found to have developed along the center plane in both the plate specimens and the I.B. specimens. The previously developed torsion-shear technique for evaluating internal bond strength of particleboard is limited to relatively thick particleboard. In particleboards 1/4-inch thick or less it was often found that the corners of the 1-inch-square specimen were crushed before the development of maximum torque. In order to obtain the maximum torque it was necessary to laminate three 1-inch square specimens or to reduce the size of the specimen. However, both lamination and small specimen size increase time and difficulty in specimen preparation and testing. This twisting-shear method supplements the torsion-shear technique and could be applied to predict internal bond strength of thin particleboard in particular. Because this method does not need gluing preparation for specimen-loading-block assembly, it could be a useful tool for quality control work in particleboard production.

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