The engineering of modern composite materials has had a significant impact on their technology of design and construction. By combining two or more materials together, it is possible to make advanced materials which may be lighter, stiffer and stronger, and better materials to end-use requirements than any other structural materials ever used before.

The structure of a wood flake composite mat may be defined as the geometric arrangement of the constituent flakes or strands in the mat. If only the mat structure is concerned, the mechanical properties of flakeboards depend primarily on the number of flake-to-flake contacts or flake-crossings and the physical properties depend primarily on the compression behavior of the mat. A better understanding of the internal mat structure will help us to characterize properties of wood composites and to utilize them more efficiently.

Wood composites require consolidation during the manufacturing process in order to reach a certain strength. This process often leads to dimensional stability problems and higher than desirable panel densities which have a negative effect on production cost and weight. A critical, but not yet well understood, factor in performance is the packing arrangement (i.e., orientation and position) of the wood elements in a mat. This factor is believed to affect the horizontal density variation (Suchsland and Xu 1989). More attention has been paid to this research area recently and a two-dimensional multi-layer flake mat model has been developed (Dai 1993, Dai and Steiner 1994a, b and c). Within this model, the formation of a short fiber composite mat was thought of as a random process due to the random nature of the constituent deposition. The structural properties of the flake network were random variables which could be characterized by Poisson and exponential distributions (Dai 1993).

However, most of the earlier studies in this area were concerned with the uniform flake geometry and completely randomized orientation of flakes in the mat, which are not realistic. These results cannot be directly applied to commercial products, such as a three-layer oriented strand board (OSB) where the flakes are partially oriented.
In this thesis, emphasis will be placed on improving understanding the relationship between horizontal density variation and structural characteristics of wood composite mats. To achieve this aim, mathematical models along with the computer simulation, robot mat formation and X-ray scanning techniques will be used. Knowledge gained from the combination of the mathematical models, simulation and predefined mat structures made by a robot, and quantitative data on density distribution scanned by an X-ray system, will help to guide improvements in present mat forming technology and also provide some perception of future wood composites development.