Issue 39

S. Doddamani et alii, Frattura ed Integrità Strutturale, 39 (2017) 274-281; DOI: 10.3221/IGF-ESIS.39.25 279 For studying the nature of crack and bonding of matrix and reinforcement it is essential to examine the fractured surfaces of all the specimens. Scanning electron microscope (SEM) is used to examine the fractured specimens of Al-graphite for the nature of fractured surface either ductile or brittle failure. Fractographic inspection was made on the fractured surface of CNT specimens for various Al-graphite composites. Fig. 4(a-d) show the fractographs of the fractured CNT specimens for various Al-graphite composites. From Fig. 4 (a-d) the failure of Al-graphite composites show dimples which grown through the matrix and are formed by void nucleation. Void nucleation cause particle rupture and debonding at the matrix-reinforcement interfaces which in turn cause the crack initiation. These micro cracks propagate from the vicinity of crack tip and passes through the matrix unstructured matrix. From experimental results it was observed that, except 12% graphite, the fracture toughness of Al6061-graphite was observed to increase with an increase in weight percent of graphite. This increase in fracture toughness is the effect of graphite particulates which act as barricade to internal cracks in the microstructure. However for 12% graphite there is decrease in the fracture toughness was observed. This decrement may be due to increased particles which causes particle clustering and the surrounding matrix. The maximum fracture toughness was found for Al6061-9%Gr and the value is 15.85 MPa m 1/2 . Figure 5: Fracture toughness of Al-Gr MMC . Fig. 5 shows comparison of fracture toughness of Al-Gr for all three specimens. From the outcomes it is observed that the fracture toughness results assessed from the CNT specimens were significant. From experimental results it was observed that, except 12% graphite, the fracture toughness of Al6061-graphite was observed to increase with an increase in weight percent of graphite. The for specimen 1 maximum fracture toughness was found for Al6061-9%Gr and the value is 15.85 MPa m 1/2 . C OMPARISON OF ALUMINIUM SILICON CARBIDE WITH ALUMINIUM GRAPHITE laneme and Aluko [3] utilized the Tensile and CNT specimens for tension testing to evaluate, respectively, the tensile properties and fracture toughness of the composite Al-SiC for 3, 6, 9, and 12 volume percent of SiC. From the experimental results obtained for both the tests it concluded that significant improvement in the strength of the Al matrix composites is achieved when 9 and 12 vol% of SiC is used as reinforcement; and the ductility of the composites is not adversely affected at these compositions in comparison with the monolithic alloy. Tab. 2 shows the comparison of fracture toughness of aluminium silicon carbide with aluminium graphite. From the comparison, it is found that the fracture toughness of the aluminium graphite is more compared to aluminium silicon carbide. Therefore, aluminium graphite can be considered as a promising material for aerospace and automobile applications where high crack arrest abilities and high strength with reduced weight is required. Further, it will contribute to crash worthy design of aircraft/automobile structures. A