Localized Modulus of Elasticity in Timber and Its Significance for the Accuracy of Machine Strength Grading
Keywords:Fiber angle, indicating property, laser scanning, machine strength grading, modulus of elasticity, strain fields
AbstractFrom previous research, it is well known that a localized modulus of elasticity (MOE) is a better indicating property (IP) of strength than an MOE averaged across a longer span. In this study, it was investigated to what extent the relationship, in terms of coefficient of determination (R2), between strength and localized MOE was dependent on the length across which the MOE was determined. Localized MOE was calculated with MOE profiles based on dot laser scanning of fiber directions, axial dynamic excitation, and a scheme of integration across a board's cross-section. Two board samples were investigated. Maximum R2 values, which were as high as 0.68 and 0.77, respectively, were obtained for localized MOE determined across lengths corresponding to about half the depth of the investigated boards. Consequently, application of a highly localized bending MOE as an IP will result in very competitive grading.
Aicher S, Höfflin L, Behrens W (2002) Determination of local and global modulus of elasticity in wooden boards. Otto-Graf-Journal 13:183-198.nAmerican Lumber Standard Committee (2013) List of approved machines. ALSC, Germantown, MD. http://www.alsc.org/untreated_machinegraded_mod.htm'>http://www.alsc.org/untreated_machinegraded_mod.htmnBechtel FK (1985) Beam stiffness as a function of pointwise E, with application to machine stress rating. In Proc International Symposium on Forest Products Research, CSIR, Pretoria, South Africa.nBechtel FK, Hsu CS, Wang N, Hanshaw TC (2006) Method for estimating compliance at points along a beam from bending measurements. US Patent 7.047.156 B1.nBoughton G (1994) Superior sorting of timber using localised stiffness on edge. Pages 510-515 in Jodie Wells, ed. Proc Pacific Timber Engineering Conference, 11-15 July 1994, Gold Coast, Australia. Timber Research and Development Advisory Council, Fortitude Valley, Queensland, Australia.nEN (2010a) EN 384 Structural timber—Determination of characteristic values of mechanical properties and density. European Committee for Standardization, Brussels, Belgium.nEN (2010b) EN 408 Timber structures—Structural timber and glued laminated timber - Determination of some physical and mechanical properties. European Committee for Standardization, Brussels, Belgium.nFoschi RO (1987) A procedure for the determination of localized modulus of elasticity. Holz Roh Werkst 45(6):257-260.nGerhards CC (1972) Relationship of tensile strength of Southern pine dimension lumber to inherent characteristics. Res Pap FPL-174. USDA For Serv Forest Prod Lab, Madison, WI.nHoffmeyer P, ed (1995) Strength grading adds value, Part 2—Available technique. Technical University of Denmark, Lyngby, Denmark. Technical Report 335-1995 [in Danish, Norwegian, and Swedish].nJohansson C-J (2003) Grading of timber with respect to mechanical properties. Pages 23-43 in S Thelandersson and HJ Larsen, eds. Timber engineering. John Wiley & Sons, Ltd., Chichester, UK.nKass AJ (1975) Middle ordinate method measures stiffness variation within pieces of lumber. Forest Prod J 25(3):33-41.nKline DE, Woeste FE, Bendtsen BA (1986) Stochastic model for modulus of elasticity of lumber. Wood Fiber Sci 18(29):228-238.nLam F, Foschi RO, Barrett JD, He QY (1993) Modified algorithm to determine localized modulus of elasticity of lumber. Wood Sci Technol 27(2):81-94.nLanvin J-D, Reuling D, Rouger F (2012) Machines for classification of wood according to strength: Presentation of different measurement techniques for grading French species (document updated 1 November 2012). FCBA Institut Technologique, Paris, France [in French].nOlsson A, Oscarsson J, Johansson M, Källsner B (2012) Prediction of timber bending strength on basis of bending stiffness and material homogeneity assessed from dynamic excitation. Wood Sci Technol 46(4):667-683.nOlsson A, Oscarsson J, Serrano E, Källsner B, Johansson M, Enquist B (2013) Prediction of timber bending strength and in-member cross-sectional stiffness variation on the basis of local wood fibre orientation. Eur J Wood Products 71(3):319-333.nOrosz I (1976) Relationship between apparent modulus of elasticity, gage length, and tensile strength of lumber. Wood Sci Technol 10(4):273-291.nOscarsson J (2012) Strength grading of structural timber and EWP laminations of Norway spruce—Development potentials. Licentiate thesis, Report No. 15. School of Engineering, Linnæus University, Växjö, Sweden. 131 pp.nOscarsson J, Olsson A, Enquist B (2012) Strain fields around knots in Norway spruce specimens exposed to tensile forces. Wood Sci Technol 46(4):593-610.nOscarsson J, Olsson A, Johansson M, Enquist B, Serrano E (2011) Strength grading of narrow dimension Norway spruce side boards in the wet state using first axial resonance frequency. International Wood Products Journal 2(2):108-114.nPope DJ, Matthews FW (1995) A comparison of deconvolution techniques to improve MOR estimation from stress grading machine output. Wood Sci Technol 29(6):431-439.nTaylor SE, Bender DA (1991) Stochastic model for localized tensile strength and modulus of elasticity in lumber. Wood Fiber Sci 23(4):501-519.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.