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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1. Introduction Wood is a material of natural origin, complex and with a high degree of heterogeneity, which makes the study of this material very complicated. This material has been used for several centuries in many domains, starting with tool handles for heavy industries such as large constructions, such as bridges. These structures are often exposed to external stresses that cause one or a combination of the three modes of fracture, i.e. mode I, II or mode III. Mode I has been studied until finally having a standardized experimental protocol which is used for the determination of two factors considered the most important and most significant in the linear mechanics of failure namely the energy restitution rate and the stress intensity factor. The DCB specimen has shown its effectiveness in the study of this mode of rupture for solid wood. In fact, many researchers, including Loulidi and Daya, who used this prototype for the characterization of solid wood in mode I, have used this prototype. Modes II and III are modes of fracture that also cause serious consequences and are still the subject of current research. This subject is still a source of inspiration for several researchers Barrett JD et al who have provided us with three experimental prototypes based on a bending test: End Notched Flexure (ENF), End Loaded Split (ELS) and Four Point End Notched Flexure (4ENF). These prototype tests have advantages but many disadvantages such as the difficulty of realization (reproducibility and repeatability), the instability of crack propagation and the length of damage in mode II is very difficult to measure visually because the crack opening produced is small. This has led us to design a new test prototype that is simple to perform and has as few disadvantages as possible.

Nomenclature G IIC Initiation fracture toughness mode II

K IIC Critical stress intensity factor mode II a Crack length d H Density of the specimen in the moisture state H d 0 Density of the specimen in the anhydrous state E l Longitudinal Young's modulus W Width of the specimen

B Thickness of the specimen E The width of the groove D The depth of the groove L Length of the specimen Z The area of fracture A Gripping area δ Displacement P Applied load Pc Critical applied load

2. Materials and methods 2.1. Material used In this study, we used logs obtained from Eucalyptus Grandis tree from Sidi Yahia El Gharb of Morocco. And who must verify the following conditions:  The diameter of the tree exceeds 30 cm at a height of 1.3 m from the ground, and 45 years old having a minimum of branches to reduce the number of knots.  The trunk must be homogeneous, and must not contain defects, parasitic attacks, rottenness or hollows.