The analytical influence of all types of knots on bending

Abstract

The influence of different types of knots and fiber deviations on the bending of wood, as managed using visual grading standards, was analytically discussed in this research by means of the finite element method. The effect of each geometrical variable on the strength and stress distribution has been studied individually. This was accomplished after validating a previously presented finite element model that accounted for the three-dimensional shape of the knots and fiber deviations. The simulated sizes and positions were those commonly managed by the standards for strength grading. The research presents the effect of: (1) the size and position of cylindrical face knots; (2) size and position of truncated conical face knots; (3) size and position of shallow conical face knots; (4) size and position of conical edge knots; (5) inclination of face knots. In each case, the analytical predictions of the modulus of rupture and stress distribution are detailed. Seven characteristic positions with distinct mechanical behavior were found, which should be accounted for in order to improve the wood grading efficiency.