Issue 41

S. Doddamani et alii, Frattura ed Integrità Strutturale, 41 (2017) 484-490; DOI: 10.3221/IGF-ESIS.41.60 488 Specimen For a/w=0.45 For a/w=0.47 For a/w=0.50 Fracture Load (P Q ) kN K Ic MPa√m Fracture load (P Q ) kN K Ic MPa√m Fracture load (P Q ) kN K Ic MPa√m Al-3%Gr 4.18 15.59 3.85 15.20 3.40 14.68 Al-6%Gr 4.35 16.22 4.05 15.99 3.50 15.11 Al-9%Gr 4.49 16.74 4.21 16.62 3.80 16.41 Al-12%Gr 4.21 15.70 4.09 16.15 3.70 15.98 Table 1: Fracture toughness of Al6061-graphite MMC for different a/w ratios. For increase in graphite content fracture toughness of Al6061-graphite for a/w = 0.45, 0.47 and 0.50 has been drawn as shown in Fig 4. From the outcomes it is found that the fracture toughness results assessed from the compact tension (CT) specimens were significant. Fracture toughness of particulate metal matrix composites is depending on particle size, interfacial strength levels and the ductility of the surrounding substance and strengthening materials. Fracture toughness testing was done using CT specimens. From the results it can be found that with increase in graphite content fracture toughness of Al6061-graphite was increased. This increment is due to the effect of increased graphite particulates which block the initiation of internal cracks in the microstructure. This increment in K Ic is consistent with the trend in most as-cast Al based particulate reinforced composites [7, 8, 12, 14]. The decrement of fracture toughness at 12% graphite may be an effect of increased graphite particles which causes particle clustering in the surrounding matrix. The decrease in fracture toughness may be due to particle debonding, interfacial cracking or particulate cracking. Figure 4: Fracture toughness of Al6061-graphite MMC Figure 5: SEM Micrographs (a) 3% graphite (b) 6% graphite (c) 9% graphite (d) 12% graphite.