Out-of-plane strand deviation in oriented strand composites

Similar to in-plane strand deviations, strand undulation through a panel thickness could adversely affect the mechanical behavior and failure mechanism of a wood-strand panel subjected to compression loads and repeated moisture cycling. The goal of this study was to characterize the out-of-plane strand deviations in an oriented strand composite to better characterize its three-dimensional structure. The results indicate that random and incidental strand undulations in the longitudinal and transverse directions are significant; these inherent attributes of oriented strand composites influence the physical and mechanical behavior of composite panels. Strand orientations through the thickness of oriented strand panels in the longitudinal and transverse directions were quantified, and the effects of strand geometry and vane spacing on these out-of-plane deviations were investigated. Discrete Fourier expansions accurately represented strand undulations through composite thickness. Location through composite thickness and length of a strand influence the distribution of undulation angles. Strands closer to the faces and shorter in length tend to result in larger undulation angles. In the transverse direction, strand deviation angles ranged between 0 and 60 degrees for the core strands and between 0 and 50 degrees for surface strands. Cumulative distribution plots indicate that smaller strand widths tend to result in higher percentages of larger undulation angles in the transverse direction for long strands. A two-parameter Weibull probability density function adequately fits both longitudinal and transverse direction strand undulation data.