On horizontal density variation in randomly-formed short-fibre wood composite boards

Abstract

Abstract A mathematical model for characterizing horizontal density variation of a short-fibre wood composite panel is derived in terms of local point density variance V(D), point autocorrelation function η(Z,λ,ω) and variance of density averages between finite sampling zones V(Ď). The point density variance is the upper-bound of zone density variance as zone size become infinitely small. Assuming random mat formation, the model predicts how the horizontal density variation changes with fibre dimensions and other processing parameters. The zone density variance V(Ď) as a monotonically decreasing function of zone size is determined by global panel density, compaction ratio (panel-to-wood density ratio), thickness ratio (panel-to-element thickness ratio), and point-to-point density correlation function which, in turn, is a function of element width and length. According to the model prediction, V(Ď) is affected by element width, length and zone size in a highly interactive manner. While increasing width and length and decreasing zone size generally cause an increase in V(Ď), the extent to which V(Ď) changes with one parameter depends on the magnitude of others. The predictive results on how the zonal density variation is affected by the processing parameters are graphically presented and discussed.