Modelling mechanical properties of spruce and Douglas fir timber by means of X-ray and grain angle measurements for strength grading purpose

Published Date

Original

First Online: 

21 January 2017

DOI: 10.1007/s00107-016-1149-4

Cite this article as: 

Viguier, J., Bourreau, D., Bocquet, JF. et al. Eur. J. Wood Prod. (2017). doi:10.1007/s00107-016-1149-4

Author

• Joffrey ViguierEmail author
• Damien Bourreau
• Jean-François Bocquet
• Guillaume Pot
• Laurent Bléron
• Jean-Denis Lanvin

Abstract

This study proposes a model using data from a scanner (X-ray and grain angle measurements) to perform strength grading. The research also includes global measurements of modulus of elasticity (obtained by vibrations and ultrasound methods), static bending stiffness and bending strength of 805 boards of Douglas fir and 437 boards of spruce. This model can be used in an industrial context since it requires low computational time. The results of this study show that the developed model gives better results than the global non-destructive measurements of the elastic modulus commonly used in the industry. It also shows that this improvement is particularly higher in the case of Douglas fir than for spruce. The comparison has been made on both the quality of the mechanical properties assessment and on the improvement of the grading process according to the European standards by using different index.

List of symbols

l

Length of the board

t

Thickness of the board

h

Height of the board

f

First natural frequency under longitudinal vibration

tsound$t_{sound}$

Travel time of the ultrasonic wave

ρ$\rho$

Board average density

G

Grey level of X-Ray Images

aρ,$a_{\rho }$ bρ$b_{\rho }$

Linear calibration coefficients of local density measurement

ρcw,${\rho }_{cw}$ ρknot${\rho }_{knot}$

Clear wood and knot density

f1,$f_1$ f2$f_2$

Parameters of the KDR calculation

KDR

Knot depth ratio: ratio between the knot’s thickness and the thickness of the board

θ$\theta$

Projection of the grain angle on the surface of the board

H(θ)$H\theta$

Function linking mechanical properties and grain angle

(EI)eff$EI{}_{eff}$

Effective bending stiffness

x, y

Local coordinates in length and height of the board

E(x, y)

Local modulus of elasticity calc. on basis of measured singularities

Em,g$E_{mg}$

Global MOE assessed by static bending with a span of 18 times the height of the board

Esound$E_{sound}$

MOE calc. on basis of the speed of an ultrasonic wave

Evib$E_{vib}$

MOE calc. on basis of the first natural frequency under longitudinal vibration

Emodel$E_{model}$

MOE calc. on basis of the proposed model for the same span as the actual static test

IPMOEmodel$IPMO{E}_{model}$

Indicating property of the MOE calc. on basis of the proposed model for the full-length of the board

σm${\sigma }_m$

Experimental bending strength with a span of 18 times the height of the board

σmodel${\sigma }_{model}$

Bending strength calc. on basis of the proposed model for the same span as the actual static test

IPMORmodel$IPMO{R}_{model}$

Indicating property of the MOR calc. on basis of the proposed model for the full-length of the board

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http://link.springer.com/article/10.1007/s00107-016-1149-4