PSI - Issue 28

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

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The behaviour of the test pieces of the petrol studied during the test may be qualified as elastic under the action of the applied load. Note that the crack propagates almost linearly until the maximum load is reached. It should also be noted that all the curves recorded show irregularities during loading which can be attributed to several reasons such as wood heterogeneity, internal defects, the variability in growth rings and the sliding of fibres between them. Cracks tend to propagate in early (low intensity) growth rings. To ensure 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 50 specimens, taking care to divide them into five batches of notch lengths “a” (a = 4;6; 8;10;12 mm). The test is carried out in controlled motion with a constant speed of 0,5 mm/min, the average tensile load decreases as the notch length increases. 3.1. Application of the energy criterion to the wood studied Our experimental approach allowed us to determine two parameters considered important in the linear mechanics of rupture: the rate of energy restitution and the stress intensity factor. To do this, we began by determining the curve of convenience based on the cut lengths used. G is the critical strain energy release corresponding to a small crack increase In an analytical form according to the IRWIN-KIES model, we write: G �� � P � 2B ∂ ∂ C a (1) When G II reaches a critical G IIC value, the rupture occurs. This criterion does not require knowledge of the stress distribution at the crack bottom, which is an advantage over the calculation of the two GII and KII parameters used in (2) Where m and C 0 are constants determined by a linear regression of the experimentally obtained complacency curve C as a function of the cube of notch length a3, then G IIC becomes. ��� � �� 2 � ��� � (3) 3.2. The critical strain energy G IIC . The critical strain energy release and the critical stress intensity factor, assuming an elastic linear behavior.The relationship between these two parameters is obtained by using a crack regression method. 3.3. The critical stress intensity factor K IIC . In Fig 4 and 5, a dispersion is observed for each value of a, except for the value of 12 mm, this dispersion is less visible. We also find that the crack propagation is stable from the ratio ( � � � ��2 ) hence a stability of our prototype for the case of Eucalyptus Grandis, we can conclude that for all the values of the ratio higher than ( � � � ��2 ), G IIC and K IIC , are characteristics of the material. In this work we have developed a new test method for the study of the behavior of the wood material subjected to a shear force in the longitudinal plane.The experimental protocol of this trial was applied to Eucalyptus Grandis. We were then able to determine G IIC and K IIC from the typical record of the displacement load curve during stable crack propagation and using the method of complacency. To validate our approach we perform microscopic analyses of the fracture facies. the overall approach. If it is noted that: � � � � �