Issue 37

M. S. Raviraj et alii, Frattura ed Integrità Strutturale, 37 (2016) 360-368; DOI: 10.3221/IGF-ESIS.37.47 366 fracture toughness increases slightly to 17.6 MPa√m. Since, Al6061+wt5%TiC composites exhibits higher yield stress compare to other two compositions as discussed in our earlier work. The results show the variation of wt% TiC reinforcement particles with Al6061 matrix significantly affects the fracture toughness. 0 2 4 6 8 10 0 1 2 3 4 5 6 7 8 9 Al+7% TiC a/W=0.5 Load, kN CMOD,mm B/W 0.2 B/W 0.3 B/W 0.4 B/W 0.5 B/W 0.6 B/W 0.7 Figure 9 : Load vs. crack mouth opening displacement curves for Al6061+wt7% TiC composite of various B/W ratios. Finally, macroscopic and microscopic observation was made on the fractured surface of CT specimens for various Al6061-TiC composites and B / W ratios. Figs. 11 (a-c) show the fractograph of the fractured CT specimens surface with magnification of 1kX for various Al6061-TiC composites of a / W = B / W =0.5. From Fig.11 (a-c) the micromechanical failure mechanisms of composites show bimodal dimples and these dimples are characteristics of failure occurring by void nucleation, growth through the matrix and coalescence indicating ductile fracture. All the particles in the vicinity of crack tip are responsible for void nucleation by particle rupture and decohesion in the matrix. The crack initiation and fracture of the composites is mainly associated with voiding in the matrix around individual particles ahead of the main crack. Void initiation is more significant in the matrix near the interface. The micro-cracks grow from these micro-voids to absorb the energy. Crack propagates by linking these micro cracks locating the crack path preferentially in the matrix adjacent to the interface can be seen in Fig.12. Figure 10 : Variation of Critical stress intensity factor vs. B/W for various Al6061-TiC composites.