Influence of structure on the elastic behavior of engineered strand composites

In modeling the behavior of wood-strand composites, influence of strand waviness or undulation through the thickness resulting from tendency of strands to conform to density variations in the panel is ignored because of analytical complexities. In this presentation, the effects of undulating strands on the elastic behavior of a wood-strand composite will be discussed and a general constitutive model to predict the elastic properties as a function of strand waviness will be introduced. A method to describe and include strand undulation in the model will also be presented. Laminates with different degrees of induced strand undulations were fabricated and tested in tension and compression. Strand undulation was shown to degrade Young's modulus of yellow-poplar laminates in both tension and compression, with more severe effects in compression. A discrete Fourier series expansion was shown to accurately describe strand undulation paths. Experimental results from compression tests were in good agreement with predictions based on the analytical model for undulatory angles of four and eight degrees. This research would add to the fundamental knowledge leading to understanding the behavior of existing wood-strand composites and development of new strand-based products.