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In this paper, the mathematical model of a jet pipe electrohydraulic flow control servo valve with a built-in mechanical feedback is developed. The actuator dynamics is also included. The solid and finite element (FE) models of the critical and precision components, feedback spring assembly and flexure tube of jet pipe assembly, were carried out first and simulated with appropriate boundary and loading conditions in a commercially available FE code, IDEAS, version 7.0, to ascertain the stiffnesses. To validate the obtained finite element results, experiments were carried out with a specially designed and fabricated test set-up. Moderately good agreement was observed between finite element and experimental values. The required simulation parameters for a jet pipe servo valve-actuator system, such as the moment of inertia, mass of the spool, mass of the piston, stiffness of the critical and precision components, and lever arm length, were obtained from the solid and finite element models. The developed model was simulated in commercially available software, MATLAB 6.5, Release 13. The step response of the valve was analysed. The simulation clearly showed the dynamics of the jet pipe, spool, and actuator displacement in achieving the equilibrium position when the applied torque and restoring torques balance, known as the steady state.

Unidirectional abrasive flow finishing process was used to finish stainless steel SS316L and titanium alloy Ti-6Al-4V materials which are widely used as implant materials. Viscoelastic polymer-based flexible abrasive media was used to finish these surfaces with different pressure and number of cycles. The obtained surface roughness and surface topography were measured using profilometer, and morphology of the surface was studied using a scanning electron microscope. Further, the wettability of the finished surface was studied by measuring the contact angle (θ) for three liquids-water, formamide, and diiodomethane using the sessile drop technique. The measured contact angles were used to ascertain the surface free energy components using Van Oss Chaudhury-Good equation. Significant difference was observed on surface roughness, contact angle, and surface energy of the machined surfaces at different finishing cycles. Also, the different tendencies of the droplet contact angle and surface energy have been observed along the direction parallel and perpendicular to the finishing direction and it gave a strong conclusion that surface roughness and surface textures play a significant role in wetting characteristics. So, this work provides an overview of the interaction between droplet and surface topography of finished SS316L and Ti-6Al-4V surfaces. Further, an empirical model has been developed using the response surface methodology (RSM) for output responses namely, average surface roughness (R a ) and material removed (MR). Interactive effects of number of cycles and pressure on average surface roughness and material removed are discussed in this paper.

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