Modelling of adequate pretwist for obtaining straight timber
- 1 June 2006
- journal article
- research article
- Published by Taylor & Francis Ltd in Wood Material Science & Engineering
- Vol. 1 (2), 76-84
- https://doi.org/10.1080/17480270600977872
Abstract
Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.Keywords
This publication has 16 references indexed in Scilit:
- Twist of wood studs: dependence on spiral grain gradientJournal of Wood Science, 2005
- Reduction in the Number of Independent Parameters for the Tsai—Wu Tensor Polynomial Theory of Strength for Composite MaterialsJournal of Composite Materials, 2003
- Modeling and smiulation of (visco)-plastic behavior of wood under moisture changeMechanics Research Communications, 1999
- The cause of the prevalent directions of the spiral grain patterns in conifersTrees, 1998
- Stress-Strain Relationship of Drying Wood. Part 1: Development of a Constitutive ModelHolzforschung, 1997
- External Heat and Mass Transfer Coefficients for Kiln Drying of TimberDrying Technology, 1996
- Drying properties and visual grading of juvenile wood from fast grownPicea abiesandPicea sitchensisScandinavian Journal of Forest Research, 1994
- Steaming under Restraint to Remove Twist in Previously DriedPinus radiataBoardsHolzforschung, 1988
- Numerical analysis of drying induced stresses in timber: An orthotropic modelMechanics of Materials, 1983
- A General Theory of Strength for Anisotropic MaterialsJournal of Composite Materials, 1971