A model of the effect of strand length and strand thickness on the strength properties of oriented wood composites

A model has been developed of the mechanism by which stress is transferred between contiguous particle components of oriented strand products such as oriented strandboard and oriented strand lumber. It is postulated that stress is transferred between contiguous strands at an angle to the glueline and that this “stress transfer angle” reduces strength properties in strand composites as grain angle reduces strength in solid wood as described by the Hankinson equation. Inclusion of the stress transfer angle into a modified Hankinson equation provides a means of assessing the interactive contributions of strand length and thickness and internal bond strength on the strength properties of composite wood products. Experimental results from a 2-ply lap joint study and multilayer high-strength oriented strand products provided good agreement with the modified Hankinson equation, which indicates that it is a useful model of the effect of strand length and thickness in the development of strength properties in composite wood strand products. Significant parameters were the parallel strength of the wood, the perpendicular strength properties of the wood and the glueline, the compressed strand thickness and the value of the experimentally determined exponent n. The initial rate of strength increase with increasing strand length increased with decreasing compressed strand thickness and increasing internal bond. The grain angle in the strands was a significant factor in the contribution of the wood strands to the parallel strength properties of the product.

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