Showing papers by "S. Sankaran published in 2012"

Microstructural and Mechanical Characterization of Two Aluminium Based In Situ Composite Foams

Abstract: In situ composites are multiphase materials where the reinforcing phase is synthesized within the matrix during composite fabrication. The present paper deals with the processing, microstructural and mechanical characterization of Al–7Si–0.3Mg–10TiB2 and Al–4Cu–10TiB2 foams. Composite foams with very low relative density (ρr = 0.17–0.37) and foams containing uniform cell sizes were successfully processed. Since the TiB2 particle sizes are less than 2 μm and have a good wetting behaviour, TiB2 can be very good foam stabilizers. Microstructural characterization of the cell walls showed significant grain refinement since TiB2 is a grain refiner. Elemental mapping clearly showed TiB2 particles at inter dendritic boundaries. Compression testing of the processed foams showed some interesting features. Stress–strain curve showed a lot of serrations which indicated brittle fracture of the cell walls and edges. Hence, it is observed that a balance should be attained between the grain refinement of α-Al grains and the amount of TiB2 particles to obtain desirable mechanical properties. Energy absorbed by the processed foams was calculated and they were observed to be close to that of the commercially available ALPORAS foams.

First Steps of Crack Initiation and Propagation in Fatigue of FCC Crystals Studied by Dislocation Dynamics

Abstract: 3D discrete dislocation dynamic (DDD) simulations are performed to simulate stage-I fatigue crack initiation and propagation along the surface, in the primary grain and its neighbouring grain, in 316L stainless steel. The scenario of crack propagation in primary grain and the evolution of dislocation structure ahead of crack tip are discussed, and in addition crack tip sliding displacement is estimated. Probable mechanisms of crack propagation from primary grain to neighbouring grain are evaluated. In this process, surface relief in the neighbouring-grain under the influence of crack stress field in the primary grain is studied for varying neighbouring-grain orientations. An enhanced evolution of surface extrusions in the neighbouring grain, are observed in the presence of heterogeneous stress field (i.e., in the presence of crack in the primary grain), compared to that in the case of homogeneous stress field. In addition, influence of crack stress field on prior cyclic-deformed substructure is presented.Copyright © 2012 by ASME