Wood shrinkage coefficient and dry weight moisture content estimations from CT-images

Abstract

The aim of this work was to try out an algorithm for estimating wood shrinkage coefficients from X-ray computed tomography images. The maximal amount of shrinkage that could occur from a green wood to oven-dry wood condition in the tangential and radial directions of the annual growth rings as well as longitudinally along the grain is expressed as a fraction of the green dimension. To estimate the shrinkage coefficients from tomography images, the wood test pieces in green state and oven-dry condition were scanned. By using an image registration algorithm, the dry wood image was thoroughly transformed to the shape of the green wood image, and the shrinkage coefficients could then be estimated. In order to try out the algorithm for moisture content calculation, a wide range of test material with different density, moisture content and size was used in the test. The material was from Pine wood, where the pieces were cut from different parts of wood logs, namely sapwood, pure heartwood, and a combination of sapwood and heartwood. The result from this transformation was compared to a tabulate shrinkage coefficient and showed a satisfactory outcome. The results show also that this method can be used to calculate the dry weight moisture content of wood from computed tomography (CT) images in a satisfactory way. The method requires wet and dry images of a wood piece. ‘Dry image’ means that the wood must be dried to zero dry weight moisture content before CT-scanning the image.