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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Matsumoto (2008), Matsumo and Nairn (2007, 2009), Rathke et al. (2012), Sinn et al. (2012), Yoshihara (2010) which takes into accond the mode II, also. Only few studies investigates the fracture of PB Ilcewicz (1979), Veigel et al. (2012). It should also be noted that, the structural integrity and the mechanical behavior of MDF may be altered significantly by the presence of cracks. Moreover, taking into account the MDF anatomy and variability, the crack path is most often subject of mixed mode crack kinematics. An understanding of the fracture phenomena under mixed-mode kinematics is also an important topic when analyzing MDF integrity. Today, several fracture approach such as the Stress Intensity Factor: Sneddon (1946), Irwin (1957), Erdogan (1962), the Crack Relative Displacement Factor Dubois et al. (2002), Dubois and Petit (2005), Pop et al. (2011), Meite et al. (2013) or the energy release rate Cherepanov (1967), Rice (1968), Budiansky and Rice (1973) allow to estimate the fracture phenomena. It should also be noted that usually the damage level can be evaluated from a local approach based on the mechanical fields assigned by the crack tip singularity or by a global approach using the mechanical fields far to the crack tip singularity. Starting from this analysis, in the present study, a formalism based on the Stress Intensity Factor and the Crack Relative Displacement Factor was applied to evaluated the fracture process. For this purpose, the Crack Opening Displacement was measured by means the Digital Image Correlation. 2. Materials and methods 2.1. Materials Medium density particleboards (PB) were tested having thickness of 16, respectively 25 mm. The density of the 16 mm thickness particleboards was 600 (±12) kg/m 3 , respectively 587 (±15) kg/m 3 for the particleboards with 25 mm thickness. All specimens were conditioned in a room at 22 0 C achieving a 65% relative humidity prior to testing. The fracture toughness data presented in literature for MDF and PB show a large scatter which could be explain by the different moisture content, specimen orientation, specimen type and testing procedure. For example for MDF with 710 kg/m 3 density the fracture toughness ranges from 2.57 MPa m 0.5 to 0.104 MPa m 0.5 which show one order of magnitude, Matsumoto and Nairn (2007). On the other hand very few mode II fracture toughness results are published in the literature. On this regard the present paper provide some experimental results on fracture toughness for both mode I and mode II loading. 2.1. Stress Intensity and the Crack Relative Displacement Factors formalism As mentioned above the fracture process was evaluated trough two parameters, the Stress Intensity Factor and the Crack Relative Displacement Factor, respectively. Based on the analytical solutions or the finite element approach, today several common solutions exist to calculate the Stress Intensity Factor Murakami (1987), Anderson (1995), which is proportional to the remote stress, the crack length and the dimensions of the sample geometry. The most common relationship allowing to estimate the SIF in opening mode (mode 1) can be defined as Anderson (1995): (1) where is the applied force; is the sample thickness; is the sample height; is a geometrical function Anderson (1995). The analysis of Eq. (1) allows us to conclude that the estimation of the Stress Intensity Factor depends on sample geometry and the loading amplitude. For geometry that is more complex the Stress Intensity Factor can be estimate from the numerical simulation by finite elements method. The second factor namely the Crack Relative Displacement Factor can be related with the kinematic state near the tip of a crack Pop et al. (2011; Meite et al.(2013). As proposed by Pop et al. (2011) and Meite et al. (2013) the CRDF           a   f B W W F K