Issue 41

S. Doddamani et alii, Frattura ed Integrità Strutturale, 41 (2017) 484-490; DOI: 10.3221/IGF-ESIS.41.60 489 The micrographs from SEM of Al6061-graphite for different composition are shown in Figs. 5 (a-d). A strong uniform microstructure between the matrix and reinforcement facilitates in the load interchange from the reinforcement to the surrounding matrix. Accordingly, crack propagation takes place in the composite via the reinforcement and not along the interface. A solid particle/matrix interface helps the graphite particles establish themselves into the matrix logically, enhancing the crack resistance. (a) (b) (c) (d) Figure 6: SEM fractographs showing dimples/voids and micro cracks propagate through the matrix and reinforcement (a) 3% graphite (b) 6% graphite (c) 9% graphite (d) 12% graphite. The fractographic image of fracture surface is shown in Fig. 6 (a-d). Higher permissible magnification of scanning electron micrographs of a fractured surface clearly exposes voids of different sizes combines with dents of different size and shape. As a result of it the void initiation will take place within the matrix that successively causes debonding of matrix and reinforcement interfaces. The direct tensile load on the composite, the microscopic voids looked as if it would have undergone restricted crack growth validating an encouraging involvement from graphite particles. Reinforcing graphite particulates in aluminum matrix force the constraints in plastic deformation. The simultaneous growth of a triaxial state of stress at the ‘local’ level assists in restricting the flow stress of the MMC. The plastic restrictions at the aluminium and graphite interfaces are mainly essential for (i) the larger graphite particulates, and (ii) clusters of the graphite particles, during failure of the composite microstructure. Investigation of the fractured surface unveils the confined destruction to be gathered at the reinforcing graphite particulates by the method of cracked particulate and decohesion at aluminium and graphite interfaces. C ONCLUSIONS he experimental study of the fracture toughness of the Al6061-graphite was conducted. From the results of this study investigation, the following conclusions are made: The maximum fracture toughness was found for Al6061- 9%Gr for a/w = 0.45 and the value is 16.74 MPa √m. Significant improvement in the strength of the Al (6061) matrix composites is achieved when 9% and 12 % of graphite is used as reinforcement. Overall, Al6061 alloy can be considered as a suitable matrix for the development of graphite reinforced Aluminium based composites. T