Issue 39

S. Doddamani et alii, Frattura ed Integrità Strutturale, 39 (2017) 274-281; DOI: 10.3221/IGF-ESIS.39.25 275 and particles. MMCs are used in automobile/aerospace applications, and also in applications requiring thermal management, wear resistance and weight reductions. Aluminium alloys is widely used for construction of aircraft structures. There are different cracks being inspected in aircraft wings. Different types of cracks inspected are: (1) Hairline cracks in the inward wing structure, and (2) Cracks at the edges of the vertical web of the feet. If the elevated forces are applied to the fasteners during assembly which are not accounted, the stress arising from the interference fit will possibly lead to cracking [10]. The particular type of aluminium alloy used will also have an effect on the assembly where a balance has to be achieved between stiffness, strength and fracture toughness. The literature survey presents a review of the published material available on the effect of various reinforcement types, their size and volume fraction, ageing behavior with Aluminium based MMCs are a combination of two phases, matrix and the reinforcement. Aluminium graphite composites for various compositions are prepared by using stir casting method [15], mechanical alloying (MI) and hot extrusion method [16] etc., and the specimens were tested for their hardness, tensile, wear and fracture properties etc. Mechanical characterization such as tensile strength and elongation experiments by using Universal Testing Machine (UTM) of Al/SiC has been reported [8] for varying mass fraction of SiCp with Aluminium. Hardness [2], Fracture toughness [3, 4], tensile fracture behavior on Circumferential Notched Tensile (CNT) Specimens [5,6] on Compact Tension (CT) test specimen [13, 14] of Al/SiC was studied by different researchers and most of them compared their results with the unreinforced aluminium alloy. In this research work, a new method of finding the fracture toughness, using Circumferential Notched Tensile (CNT) Specimens, is utilized which is a recent advance in fracture toughness testing method is adopted. From the literature it is observed that relatively more work has been done on the tensile and fracture characteristics of aluminium silicon carbide particulate MMCs. However, a significant scope exists for research on the aluminium matrix composites reinforced with graphite particles, particularly in the area of fracture and fatigue in order to improve the strength and fracture characteristics of the material to avoid the cracking. In this backdrop, the current research work is proposed to study the fracture toughness of aluminium 6061 graphite particulate composite at varied weight fractions. The specimen are prepared using stir casting method with graphite proportions of 3 to 12 % by weight. The specific objective of the research work is to study the fracture toughness of the aluminium graphite MMC at varied weight fractions of graphite (3%, 6%, 9%, and 12%) experimentally using Circumferential Notched Tensile (CNT) specimens. Also an attempt will be made to compare the results of Al6061-graphite composites with the Aluminium Silicon carbide particulate (Al-SiCp) composites. M ATERIALS he material chosen for this research work is aluminium 6061 as matrix and graphite particles as reinforcement. The motivation to use these materials for this research work is the density of two materials involved, which are nearly same for aluminium (2.65g/cc) and graphite (2.2g/cc). The Al6061-graphite particulate composites have discontinuously reinforced composite properties which are nearly isotropic and also have outstanding combination of mechanical, structural, thermal and physical properties. Figure 1: Schematic view of stirring mechanism used in the fabrication of MMC [15]. T