PSI- Issue 9

Liviu Marsavina et al. / Procedia Structural Integrity 9 (2018) 47–54 Author name / Structural Integrity Procedia 00 (2018) 000–000

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displacement control with a loading speed of 10 mm/min. The Single Edge Notched Bend (SENB) specimen’s average size are given in Table 1.

Table 1. Single Edge Notched Bend Specimen sizes. W (mm)

a (mm)

B (mm)

L (mm)

Sample geometry

50.12

24.6

23.6

192

Mode II fracture toughness tests . Compact shear (SC) specimens Fig. 3.b were used for mode II fracture toughness determination. Tests were performed on a LBG 100 kN universal testing machine, at room temperature and under displacement control. The Compact shear (SC) specimen’s average size are given in Table 2.

Table 2. Compact Shear Specimen sizes. W (mm)

a (mm)

B (mm)

H (mm)

Sample geometry

50.14

25.12

16.4

76.18

3. Results Figs. 4.a et 4.b shows the experimentally load – crosshead displacement specific curves for two specimens, Single Edge Notch Bend and Compact Shear, respectively. The analysis of results presented in Fig. 4 lead us to conclude that the specimen failures are not a brittle failure. Additionally, the presence of mixed mode (i.e. opening and shear modes) during the cracking process can appear following the wood fibers orientation. It is for this reason too that in the present study the uncoupling of mixed modes is proposed to characterize the fracture parameters. From the force/displacement curve, shown in Fig. 4 the evolution of energies are plotted. In this case, the total strain energy is equal to the area under the force/displacement curve. The elastic strain energy is assimilated with the energy that may be recovered when loading is gradually removed. In the graph of energy evolution it can be seen a significant amount of dissipated energy during the damage process. However, this previous approach does not take into account the boundary conditions or the presence of the mixed mode. Under these conditions, we propose to evaluate the fracture energy by using the formalism based on the Stress Intensity and Crack Relative Displacement factors, proposed by Pop et al. (2011), Meite et al. (2013). As indicated in the first part of the paper the Stress Intensity Factor for the opening mode was estimated using Eq. 1. For the Compact Shear specimen the Stress intensity Factor was calculated from the finite element analysis. The geometric characteristics of specimens needed to calculate SIF were given in Table 1 and 2. The average Stress Intensity Factor values corresponding to Single Edge Notched Bend and Compact Shear specimens are given in Table 3. Considering Eq. (2), the average Crack Relative Displacement Factor values were calculated for the maximum loading Pop et al. (2011), Meite et al. (2013). The results resumed in Table 3 show that the adjustment procedure allows to extract the fractures parameters corresponding to opening and shear modes. As indicated in Table 3 the specific total energy was calculated from the load-crosshead displacement curves.

Table 3. Fracture parameters.

Mode 1 0.87

�� ����� � √ )

Mode 2 ��� ���� � √ )

Mode 1 0.138

� ��� � �� )x10 -3

Mode 2 � ��� �� �� � x10 -3 0.0011

Sample

Specific energy (N/mm)

Single Edge Notched Bend

0

1875 1015

Compact Shear

0.11

0.62

0.105

0.012