Investigation of Shrinkage in Softwood Using Digital Image Correlation Method

Abstract

Distortion in lumber, such as twist, cup, spring and bow, can cause serious problems for its use in service. Lumber distortion is largely a result of differential shrinkage in wood in different directions and the presence of different types of wood (i.e. juvenile and mature wood) in a single piece. Shrinkage varies within tree because of different types of wood. In this paper, the digital image correlation (DIC) method was used to investigate shrinkage variation within tree. The DIC method is an image-based, non-contact and full-field displacement and strain measurement method. Two softwood species grown in Eastern Canada, jack pine and white spruce, were used in this study. In this paper, average full-field shrinkage over each growth ring was measured, and the growth ring position in relation to pith of the tree was recorded. The shrinkage variations in the radial, tangential and longitudinal directions in a tree stem are presented. The work described in this paper is part of a larger study to develop a modeling technique to predict distortion of lumber based on its position in a tree stem.