Issue 39

S. Doddamani et alii, Frattura ed Integrità Strutturale, 39 (2017) 274-281; DOI: 10.3221/IGF-ESIS.39.25 276 P ROCESSING luminium 6061-graphite specimens are prepared at varied weight fractions of graphite (3%, 6%, 9%, and 12%) using stir casting method. The aluminium blocks were melted in the furnace as shown in Fig. 1. After melting, molten aluminium was super-heated to desired temperature (about 750 0 C). The required amounts of graphite particles were added to the aluminium melts while stirring with stirrer at speed of 550 rpm. The molten aluminium-graphite was poured into a split type permanent mould and it was allowed to solidify. The aluminium-graphite alloy bars were taken out from the mould. The specimens were prepared from as-cast alloys for determination of required properties. E XPERIMENTATION o investigate the fracture toughness, there are different methods. Basically American Society for Testing and Materials (ASTM) standards and recent advances in fracture toughness testing methods are used for testing of aluminium alloys and some of aluminium matrix particulate reinforced composites. ASTM standard testing methods include Fracture toughness testing by Single1Edge1Notch Bend (SENB) Specimen and Compact Tension (CT) Specimen. Other testing methods which are getting popular for their ease include Fracture toughness by Circumferential Notched Tensile (CNT) specimens, Round Bar, and Indentation techniques. Figure 2: Schematic representation of the CNT specimen [13]. Circumferential Notch Tensile (CNT) specimen shown in Fig. 2 was fabricated for estimation of fracture1toughness, in a manner confirming with Alaneme and Aluko [3]. The CNT samples were machined for the following dimensions: sample diameter D=12.5mm, notch diameter d =11.24mm, gauge length L =62.5mm, and notch angle α =60°. The test samples were subjected to tensile test on UTM for the determination of fracture toughness. The load at fracture (P f ) acquired from the CNT specimens load-expansion plots (Fig. 3) were utilized to assess the fracture toughness [3] by applying observational relations by Dieter: IC K f 3/2 P D D 1.72 1.27 d               (1) where, P f = load at fracture, in N D = specimen diameter, in mm and d = notch diameter, in mm. In accordance with Nath and Das [11], the reliability of the CNT testing method and the achievement of the plane strain condition were evaluated using the relations: IC y K 2 D           (2) A T