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    • Design of textured surfaces for super-hydrophobicity

      PRITHVI RAJ JELIA AMIT AGRAWAL RAMESH K SINGH SUHAS S JOSHI

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      Although the Cassie–Baxter and Wenzel equations predict contact angles for relative dimensions of micro-pillars on textured surfaces, the absolute pillar dimensions are determined by trial and error. Alternatively, geometries of natural super-hydrophobic surfaces are often imitated to design textured surfaces. Knowing the limitations of both the approaches, this work presents a constraint minimization model on the basis of Cassie–Baxter equation to determine the absolute dimensions of square micro-pillars on a textured surface so as tomaximize the contact angle. The constraints are derived based on the limiting physical conditions at which spontaneous breakdown of super-hydrophobicity takes place. The single-droplet numerical simulations on textured surface gave the duration for which super-hydrophobicity is sustained. The model demonstrated that the round edged pillars, arising out of fabrication imperfections, reduce the height of the pillars without significantly compromising on the contact angle. The measurement of contact angle on the fabricated textured surfaces wasfound to be in agreement with the model predictions when the fabricated pillars had fairly uniform dimensions.The proposed approach is sufficiently general that its application can be extended to design other textured surface

    • Analytical modeling of exit Burr in drilling of Ti6Al4V alloy

      ANKIT RANA GANESH DONGRE SUHAS S JOSHI

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      Burrs affect precision components and cause assembly related problems, and in general, decrease manufacturing productivity. Drilling burr formation involves multiple stages that are influenced by variation in thrust forces, temperature, stress conditions, and deformation modes in the unsupported length of the workmaterialbelow the drill. Several of these have not been adequately investigated so far. Therefore, the objective of this work is to model the complex phenomena that occur just before the exit of the drill tip from the bottom surface of the hole, and up to the complete exit of the drill point from the work surface. Accordingly, two models have been developed: (i) to estimate onset of bending in conjunction with theory of plasticity, which leads to the formation of a small drill cap under the pressure of steady-state drilling thrust forces, and (ii) to evaluate exitburr size that involves stretching and bending of a thin layer below the drill tip, using the principle of energy conservation. It is observed that a fracture is initiated at the chisel edge corner resulting in the formation of a small drill cap. The exit burr size predicted by the model is within one standard deviation from the average burrheight as determined from the experimental data.

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