Non Destructive Test Sample Preparation for Mechanical Properties

49 After setting the acquisition device, the tested samples were first weighted and measured in length, width and height. Then the samples were positioned on the two elastic bearings like shown in the Figure 26 and made sure that the supports were located at a distance of ¼ of the total length of each specimen. Afterwards the microphone was set up in perpendicular with the length of the samples see Figure 26 with the distance of 1 or 2 cm from the sample. The samples were hit by percussion bar at one end of the sample and the sound emitted was recorded in another end of the samples by microphone. The emitted sound from the end of the samples was converted into electrical signal by the microphone. This signal was then amplified and filtered by means of the acquisition card acting as an analog-digital converter and which delivered to the computer to digitize the signal. Figure 26 Samples placement on BING bending vibration method After digitizing the signal, then it was recorded and transferred to a users computer memory. The spectral composition of the recording was given by fast fourier transform, the spectral width of the acquisition depends on fixed parameters point number and acquisition time. The mathematical calculation of the selected frequency was performed via software from the geometric characteristics and mass of the sample. It was used to determine the elastic moduli by Bernoulli and Timoshenko models. Timoshenko model was used in several studies Bordonné 1989; El-Houzali 2009 including this research. Timoshenko had an equation of motion that took into account the bending moment, shear, and rotational inertia. Bernoullis model did not take into account either the shear or rotation inertia. This model was a simplified model of Timoshenko where we considered the strain energy due to the negligible shear during bending.

4.5.4.2 Destructive test

Four-point bending tests were performed on an INSTRON universal testing machine Figure 27 to measure MOE static and Modulus of Rupture MOR. Moisture content values of poplar cultivars and douglas-fir samples were 8.5 ± 0.5 and 13.3 ± 1.6, respectively. The moisture content values were uniform when the destructive tests were performed. Specific MOE and specific MOR were obtained by dividing static MOE and MOR by the LVL density at those moisture content values. 50 4.5.5 Statistical Analysis 4.5.5.1 Statistical Analysis of poplar LVL Density, MOE, MOR, Specific MOE SMOE and specific MOR SMOR were the observed parameters. The experimental results were statistically analysed using an analysis of variance ANOVA to analyze the effects of veneer thickness 3 mm and 5.25 mm, poplar cultivars, juvenility juvenile and mature and loading direction edgewise and flatwise. Mean differences between levels of factors were determined using Duncan’s Multiple Range Test. a b c Figure 27 Schematic diagram of destructive test for LVL from poplar cultivars and douglas-fir: four point bending test a; flatwise direction b; and edgewise direction c

4.5.5.2 Statistical Analysis of douglas-fir LVL

Density, MOE and MOR were the observed parameters. The experimental results were statistically analysed using an analysis of variance ANOVA to analyze the effects of veneer thickness 3 mm and 5.25 mm, juvenility juvenile and mature and loading direction edgewise and flatwise. Mean differences between levels of factors were determined using Duncan’s Multiple Range Test

4.6 Results and Discussion for sengon and jabon LVL

4.6.1 LVL density

LVL density increased from pith to bark for LVL made of unboiled and boiled veneers of sengon and jabon Figure 28a-b. The average sengon LVL density of unboiled and boiled type I were 370.1, 401.1, kgm -3 respectively. Otherwise, the average sengon LVL unboiled and boiled type II were 391.4 and 408.1, respectively Figure 28a. The average jabon LVL densities were 473.7 kgm -3 unboiled type I, 494.4 kgm -3 boiled type I, 497.6 kgm -3 unboiled type II, and 520.3 kgm -3 boiled type II Figure 28b. Load bending Load bending