Srinivasarao Lathabai

Influence of microstructure on the erosive wear behaviour of Ca α-sialon materials

The erosion behaviour of three pressureless sintered Ca α-sialon ceramics with different grain sizes, morphologies and various amounts of grain boundary glass was investigated using a gas-blast type erosion rig. The erodent particles used were SiC grits. The effects of grain size and morphology on the erosion mechanism were studied. It was found that the dominant material removal mechanism for the fine equiaxed-grained sialon was grain dislodgment, while that for the elongate-grained material was transgranular fracture. The effect of different amounts of intergranular glass on the erosion resistance of these materials was also studied. It was found that an optimum amount of grain boundary glass had a beneficial effect on erosion resistance. Finally, the effect of post-sintering heat treatment on the erosion behaviour of these materials was investigated. The results showed that heat-treated samples exhibited a higher erosion rate than their as-sintered counterparts.

Compliance analysis of a bridged-crack under monotonic and cyclic loading

Abstract A systematic approach for crack bridging in quasibrittle materials, such as coarse-grained alumina ceramics, is extended to study frictional degradation in grain bridges during cyclic fatigue. It is shown that the variation in bridging stress owing to the grainbridge degradation can be determined in terms of compliance measurements. Parallel to the bridging theory under monotonic loading, the extended analysis under cyclic loading is divided into two parts: i.e. the pure frictional degradation of existing bridges without any crack growth, and the coupling problem of the establishment of new bridges accompanying fatigue crack growth and degradation of old bridges subject to cyclic fatigue. Preliminary results on bridging stresses in a coarse-grained alumina under monotonic loading are obtained with the bridging theory.