PSI - Issue 28

A. Saoud et al. / Procedia Structural Integrity 28 (2020) 491–501 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The behavior of specimens can be qualified as elastic under the action of the applied load. To guarantee the validity of our results and to take into account the known dispersion of the wood, the tests were carried out on a set of more than 70 specimens, taking care to divide them into five batches of specimens of notch length “a“ (a = 40; 50; 60; 70; 80; 90; 100mm). The test is carried out in controlled displacement with a constant speed of 0.2 mm / min, as previously announced, the average load decreases as the length of the notch increases, 4.2 The critical strain energy release G IIC and the critical stress intensity factor K IIC . To carry out our calculations we adopted the same assumptions as for the previous test specimen studied. The complacency method is frequently used to determine the rate of energy release. This is the definition of a relation describing the evolution of the compliance of the sample (C) according to the length of the crack (a) during loading. In the case of the 4ENF test, the relation C = f (a) can be shown to be given by a linear function. The complacency in our case is then written in the form: C � C � a � C � (4) Where C 1 and C 2 are coefficients to be determined by linear regression. Considering the IRWIN-KIES relationship. G �� � P � 2B ∂ ∂ C a (5) The critical strain energy release then becomes: �� � � � 2 (6) In order to better understand the fracture process that the 4ENF specimen underwent, we plotted the GIIC and KIIC curves as a function Mf the notch lengths respectively in Fig 9 and 10.

Fig .9. Evolution of the critical energy release rate G IIC as a function of the length of the notch

On the fig 9 and 10, we observe a dispersion for each value of a, especially for the values of 50 mm and 90 mm this dispersion is then very visible. It is also noted that the propagation of the crack is almost stable until arrivers with a report. � �� � ���� These Figures show the relationship between the parameters K IIc and G IIC and the length of the crack a. Analysis based on fracture mechanics is essential even for small notch lengths. However, the dependence of these parameters on the lengths of the defect is very significant for small cracks, i.e. if one could repeat the estimates of KIIC and GIIC