Veneer selection and panel composition of douglas-fir

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4.5.4 Sample Preparation for Mechanical Properties

Each board was cut into standardized test samples EN 789, parallel to grain with total of 1808 samples for poplar and 140 samples for douglas-fir Figure 25. Figure 24 Glue machine and gluing process a and cold press b Figure 25 Preparation samples for non destrustive and destructive test a; and samples for bending properties b The parameters for mechanical properties were Modulus of Elasticity MOE and Modulus of Rupture MOR. First, dynamic tests BING was performed then a static 4-point bending test was performed for each sample.

4.5.4.1 Non Destructive Test

Dynamic analysis is a simple and efficient way of characterizing the Module of Elasticity MOE of many materials, including wood Brancheriau and Bailleres 2002; Bucur 2006. In order to estimate the dynamic MOE from non- destructive test method, bending vibration method BING was used for the 1808 samples poplar cultivars and 140 samples douglas-fir. This is a fully automated system designed by CIRAD-Forêt following work of Bordonné 1989 and Hein et al . 2010. It is based on measurement and interpretation of the natural frequencies of vibration from a wood piece subjected to impulse loading. This method was easy to apply, very quick and practical. The dynamic MOE were obtained through percussion bending perpendicular to the glue joints in two loading position flatwise FW and edgewise EW. The interpretation of the spectrum of the natural frequencies was based on the fact that the ratio of elastic modulus to density specific modulus of a material was proportional to the speed of signal propagation in the material. BING method could be divided into three interrelated steps: 1 begins with a general initialization of the equipment and preparation the samples; 2 the acquisition and analysis of the digitized signal; and 3 the mathematical and mechanical processing of the signal. a b a b