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European Journal of Wood and Wood Products

, Volume 73, Issue 1, pp 17–27 | Cite as

Local variation of modulus of elasticity in timber determined on the basis of non-contact deformation measurement and scanned fibre orientation

  • Min HuEmail author
  • Marie Johansson
  • Anders Olsson
  • Jan Oscarsson
  • Bertil Enquist
Original

Abstract

During the last decade, the utilization of non-contact deformation measurement systems based on digital image correlation (DIC) has increased in wood related research. By measuring deformations with DIC systems, surface strain fields can be calculated. The first aim of this study concerns the possibility to detect detailed strain fields along the entire length of a wooden board subjected to pure bending and the potential of using such strain fields to determine a bending modulus of elasticity (MOE) profile along a board. Displacements were measured over 12 subareas along a flat surface of the board. For each such area, a separate local coordinate system was defined. After the transformation of locally measured coordinates to a global system, high resolution strain fields and a corresponding bending MOE profile were calculated. A second method in establishing bending MOE profiles is to use fibre angle information obtained from laser scanning and a calculation model based on integration of bending stiffness over board cross sections. Such profiles have recently been utilized for accurate strength grading. A second aim of this study was to investigate the accuracy of the bending MOE profiles determined using the latter method involving fibre angle information. Bending MOE profiles determined using the two described methods agree rather well. However, for some patterns of knot clusters, the local bending MOE, calculated on the basis of fibre angles and integration of bending stiffness, is overestimated. Hence, this research adds knowledge that may be utilized to improve the newly suggested strength grading method.

Keywords

Digital Image Correlation Fibre Orientation Wood Surface Fibre Angle Load Stage 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols

El

MOE in the local longitudinal fibre direction

Ex

MOE in the global x-direction, i.e. the direction of the board

Eb

Average bending MOE over cross-sections along the global x-direction, also referred to as bending MOE

EIz

Bending stiffness over cross sections with respect to the global z-direction

εx

Normal strain in the global x-direction

εy

Normal strain in the global y-direction

εxy

Shear strain in the global xy-plane

Notes

Conflict of interest

The authors declare that they have no conflict of interest.

References

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Min Hu
    • 1
    Email author
  • Marie Johansson
    • 1
  • Anders Olsson
    • 1
  • Jan Oscarsson
    • 2
  • Bertil Enquist
    • 1
  1. 1.Department of Building TechnologyLinnaeus UniversityVäxjöSweden
  2. 2.SP Wood Technology, SP Technical Research Institute of SwedenVäxjöSweden

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