Timber is a composite material ordered over many length scales. The basic building blocks of timber are wood fibres, hollow tube like elements which are responsible for both water transport and load bearing within trees, (Ansell, 2015). The fibres can be separated from bulk timber in a process known as defibrilation, a key industrial process for the production of Medium Density Fibreboard (MDF). MDF is a composite material formed of fibres and adhesive, which is used widely in the construction industry among innumerable others.
Wood fibers are of the order of a few millimeters in length and a hundred micrometers in width, which makes it difficult to mechanically characterize them using standard methods, such as tensile testing. This work, builds on the development of a novel method to evaluate the stiffness of wood fibers, which uses the cantilever of an atomic force microscope (AFM) to carry out three-point bending. This is done by placing the fibers across a two millimeter trench, whereupon the AFM engages to the center and both applies loads and records the resulting displacements. Testing using this method has been confined to a single species of wood, pinus sylvestris (Scots pine), but there is a significant spread in the modulus of the fibres tested. This is not entirely surprising as a sample of wood consists of several different types of fibre, including, for example, heartwood and sapwood, early wood and latewood. These different fibres vary slightly in size and wall thickness. Here, Weibull statistics is used to investigate the correlation between samples in a dataset, and describe the magnitude of the correlation, in order to distinguish between fibre types and to provide greater clarity of the modulus associated with different types of fibre.