20 A. K. Pandouria et al. 3.2 Material and Specimen Preparation A three-point bend specimen (TPB) is widely used to evaluate fracture toughness of high-strength materials. The material under evaluation for this chapter is Al6063-T6. The chemical composition and static mechanical properties of Al6063-T6 are presented in Tables 3.1 and 3.2. The specimen for these experiments is designed according to standard ASTM E399 standard [7]. A schematic diagram of the three-point bend specimen (TPB) is shown in Fig. 3.1. The Crack length, a, is nominally between 0.45 and 0.55 times the width, W. TPB specimens can have a width to thickness (W/B) ratio of 1 ≤W/B≤4. The specimen dimensions used in this study are: thickness (B) =10 mm, width (W) =20 mm, span (S) =80 mm, and total length (L) =100 mm. It should be noted that before conducting the experiments, fatigue precrack was done in L-T direction of the specimen, so that the total crack (Notch +Fatigue Crack) should be 50% of the width of the specimen. 3.3 Experimental Procedure 3.3.1 Quasi-Static Test Static three-point bend tests were performed on a zwick/Roell Universal Testing Machine (UTM). The applied load was measured using a load cell of 100kN capacity, and the crack mouth opening displacement was measured using the 3D DIC technique. A detail of the static experimental setup coupled with two low-speed cameras is shown in Fig. 3.2. The static stress-intensity factor (SIF) for three-point bend specimen is calculated using the following formula [3.1]: K1 = 3S√a 2BW2 Y a W F (3.1) where Y a W = 1.99− a W 1− a W 2.15−3.93 a W + 2.7 a W 2 1+2 a W 1− a W 3 2 Table 3.1 Mechanical properties of Al6063–T6 alloy Young’s modulus E, GPa Yield strengthσys, MPa Ultimate strength σUTS, MPa Poisson’s ratio Elongation at break δ,% Mass density ρ, kg/m3 68.9 214 241 0.33 12 2700 Table 3.2 Average chemical composition (Wt. %) of Al6063-T6 alloy Element Al Si Cu Mg Fe Zn Ni Mn Ti %Wt. 98.55 0.431 0.0069 0.5431 0.3982 0.0153 0.0058 0.014 0.0056 Fig. 3.1 Schematic of 3-point bend specimen
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