Modelling of Knots and 3d Fibre Orientation within Timber Boards Based on Information Obtained from Optical Scanning

Abstract

In sawn timber, the presence of defects, mainly knots, cause the fibres to deviate from the longitudinal direction of the board and thereby lead to a significant reduction of strength and stiffness. Hence, the aim of the present research was to develop a method and algorithm to mathematically represent the orientation of fibres at any point on a 3D growth surface in the surroundings of knots and within geometrically reconstructed timber boards. The entire procedure consisted of three automatic steps, namely 1) detection of knots on board surfaces, 2) modelling and reconstruction of knots in 3D and 3) application of a novel model for fibre orientation in the surroundings of knots. The curved geometry of knots was taken into account, and the fibre orientation, at any point within the board, was calculated solely as a function of the shape of the growth surface at that point. The proposed function for fibre orientation enabled a physically feasible definition of fibre deviation zone, which was related to the geometry of the modelled growth surface, i.e. the knot bump caused by the occurrence of a knot. Validation of the proposed method for modelling of 3D fibre direction in timber boards was performed using a total sample of 100 boards of Norway spruce. The results presented show a very good agreement between model-obtained and experimentally-obtained in-plane fibre directions.

Keywords: Sawn timber, Knot detection, Curved knot modelling, 3D knot reconstruction, 3D fibre orientation modelling