• K Neelakantan

      Articles written in Bulletin of Materials Science

    • Details of an imaging atom probe

      V R Seshadri K Neelakantan E Mohandas V S Raghunathan

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      An imaging atom probe has been incorporated in a conventional field ion microscope in our laboratory. The principle and instrumentation of the probe has been discussed.

    • Computer simulation of serrated yielding

      K Neelakantan

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      A model for serrated yielding based on the negative resistance characteristics of materials is discussed. An analog computer based on this model is described. The simulated curves show oscillations which are regular and uniform in amplitude. To simulate more realistic tensile test curves, a refined model which includes the effects of fluctuations in dislocation density and velocity is described. Some simulated curves using this refined model are presented. These results are close to observed tensile test curves.

    • Simulation of serrated yielding with noise effects included

      K Neelakantan G Venkataraman

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      The phenomenon of repeated yield drops is extensively studied using computer simulation. The basic input is the Cottrell-Bilby model for dislocation drag, used in conjunction with a suitable scenario for work hardening. Stochastic effects associated with dislocation velocity and density are built in via multiplicative noise. Using the above scheme for modelling the plastic response and assuming first that the yielding is homogeneous, the machine equation is solved for successive time steps to obtain complete stress-strain curves, similar to those obtained in laboratory experiments. Real-life patterns are well simulated, including several detailed features observed in diverse experiments. The role of noise in the region of marginal stability is explored. The simulation study is next extended to the case of inhomogeneous yielding where, in addition to the model earlier proposed by Penning, we explore one which takes some account of dislocation flow across the sample. Attention is then drawn to similarities observed in the flow of sand in a sand pile. Finally, some suggestions are made for further work.

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