PSI - Issue 17

S. Mousa et al. / Procedia Structural Integrity 17 (2019) 284–291 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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materials (FGM) are a good choice. FGMs are multi-phase materials in which the volume fraction of the constituents in the material varies as a function of position. Functionally graded materials (FGMs) are new generation of engineering materials wherein the material composition varies gradually in some directions to achieve unique mechanical, thermal and electrical performances different from those of homogeneous or joined dissimilar materials. FGMs are ideal candidates for the applications requiring multifunctional performance. Due to the variation of properties, the fracture behaviour in FGMs is complex (Jin, Wu et al. 2009). In addition to the material and manufacturing process development efforts for functionally graded materials, significant research has also been taking place in the areas of analytical, numerical and experimental methods to understand the mechanical behaviour of FGMs under different geometry and loading conditions (Delale and Erdogan 1983, Erdogan 1995, Ozturk and Erdogan 1996, Schulz, Peters et al. 2003). Comi and Mariani (2007) using composite specimens with notched mid-span cross-sections, featuring a material gradient parallel to the pre-crack, were subjected to 4-Point bending test. The inclusion volume fraction varies along the gradient between V f = 0.0 at the so-called compliant side (due to the lower E value of the matrix phase) and V f = 0.5 at the so-called stiff side. Sharp pre-cracks were cut either at the compliant or at the stiff specimen sides. From the numerical outcomes it appears that the specimen featuring the pre-crack at the compliant side is more resistant to crack advancement than the specimen featuring the pre-crack at the stiff side (Comi and Mariani 2007). Jin, Wu et al. (2009) investigated the mixed-mode fracture response of ZrO 2 /NiCr functionally graded materials. They found that: (1) prior to crack initiation, the increasing elastic modulus ahead of crack-tip can enhance the mode mixity at crack-tip; (2) the crack with the increasing elastic modulus ahead the crack-tip kinks less than the one with the decreasing elastic modulus, which is caused by the elastic gradient and the local fracture toughness; (3) the heterogeneity in microstructure can cause the local perturbation but has no obvious effect on the overall crack propagation path. Jin and Noda (1994)observed that the asymptotic stress field near the crack-tip in a FGM is identical to that in a homogeneous material, i.e. the Williams (1957) solution. However, as the distance from the crack-tip increases, the higher-order terms are affected by the material gradation. The material gradation does not affect the order of singularity and the angular functions of the crack-tip fields, but does not affect the stress intensity factors (SIFs) as described by Shim, Paulino et al. (2006). The influence of the elastic gradient on the stress intensity factor (SIF) for cracks in graded materials is very well established (Erdogan 1995, Gu and Asaro 1997). There are many investigations addressing the effect of the elastic gradient on the crack tip stress and displacement fields in graded materials (Parameswaran and Shukla 2002, Jain, Rousseau et al. 2004, Kubair, Geubelle et al. 2005, Chalivendra 2008). Gu and Asaro (1997) studied crack deflection in FGMs where the crack plane is perpendicular to the material gradient direction. They Dry (1996), Ozturk and Erdogan (1996) studied the effect of notch depth on J-integral and critical fracture load in a plate made of functionally graded aluminium – silicon carbide composite (Al – SiC) with U-notch under bending. The results indicated that in the case where the notch side is toward brittleness increment the critical J-integral in functionally graded material (FGM) is larger than that of homogeneous material with the same mechanical properties at the notch tip. Therefore, FGM is more convenient than homogeneous material against fracture. The main objective of the present work is to study the effect of pre-crack inclination angle of FGM specimen on the crack growth and final failure shape under three-point bending, 3PB, numerically and experimentally. 2. EXPERIMENTAL WORK The polymeric matrix with varying fiber distribution are used to obtain the graded composite material. The hand lay-up technique was used to manufacture the graded material. Therefore, we propose a methodology to design and manufacturing the FGM by hand lay-up method using the composite material technique. The polyester polymer was used as matrix with long glass fibres. The FGM were manufactured by using the unidirectional glass fiber-polyester polymeric prepregs and consists of 12 laminas (with 6±0.1 mm thickness) depends on varying the distance between the glass fiber along the polyester polymeric matrix within the each laminate. The distance between the glass fiber is very narrow at the outer of the specimen and it is large at the inner of specimen (as shown in Fig. 1), to obtain a high resistance to bending stress. The mechanical and physical properties of E-glass fiber and polyester resin are shown in table 1.