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Finite element study of growth stress formation in wood and related distortion of sawn timber

Ormarsson, Sigurdur; Dahlblom, Ola LU and Johansson, Marie (2009) In Wood Science and Technology 43(5-6). p.387-403
Abstract
Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral... (More)
Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Wood Science and Technology
volume
43
issue
5-6
pages
387 - 403
publisher
Springer
external identifiers
  • wos:000268729400004
  • scopus:68749120978
ISSN
1432-5225
DOI
10.1007/s00226-008-0209-2
language
English
LU publication?
yes
id
96e2dd3d-238c-4de7-8aeb-7578bfc82379 (old id 1477498)
date added to LUP
2009-09-22 15:21:41
date last changed
2017-10-29 04:01:53
@article{96e2dd3d-238c-4de7-8aeb-7578bfc82379,
  abstract     = {Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain.},
  author       = {Ormarsson, Sigurdur and Dahlblom, Ola and Johansson, Marie},
  issn         = {1432-5225},
  language     = {eng},
  number       = {5-6},
  pages        = {387--403},
  publisher    = {Springer},
  series       = {Wood Science and Technology},
  title        = {Finite element study of growth stress formation in wood and related distortion of sawn timber},
  url          = {http://dx.doi.org/10.1007/s00226-008-0209-2},
  volume       = {43},
  year         = {2009},
}