Dr. Ajith Ramesh

In this paper, finite element simulations of spherical indentation of Nickel thin film on Steel-4340 are studied for single and multiple cycle of indentation as well. The objective was to understand the mechanics of coated systems, from load-displacement (P-h) curves, stress distribution in the film and the effect of substrate yield strength on the indentation response. The loading portion of P-h curve showed displacement bursts and the reason for this is investigated. A transition in the deformation behavior of the film from Hertz-type to flexure was observed for a normalized indentation depth of h/tf ≈0.2. The influence of coating–substrate properties on P-h curve is also investigated for different h/tf ratios and yield strains. Attempts are also made to explore the possibility of understanding the creep-fatigue behavior of coated specimen subjected to cyclic indentation at room temperature from Indentation depth v/s time, Indentation depth v/s number of cycles and Plastic dissipation energy v/s number of cycles curve.

This dissertation presents a detailed model of the ‘overall’ behavior of Torsional springs. Torsional springs (also called ‘Clock’ springs) are a kind of spiral springs which are supposed to provide a certain torque when wound-up to a certain rotation. However, it is observed that the moments that are developed relax when the springs are kept loaded over long periods of time. The research presented here is an attempt to investigate this behavior by identifying the role played by the various influencing parameters.

The dissertation focuses on the development of a detailed component-level finite element model to investigate the instantaneous moment-rotation response as well as the long-term (time-dependant) structural response of a torsional spring. Torsional springs belong to a class of planar spiral springs that are commonly made out of Elgiloy - an alloy of Cobalt, Chromium, Nickel, and Iron. Elgiloy has very high yield strength, and is commonly used as a spring material in analog clocks. In addition, the research also aims at developing a better understanding of the dependence of the response of the spring on the different design parameters that define its geometry and material properties. Frictional contact, large deformations, and nonlinear material behavior (plasticity and creep) are among the major challenges that need to be resolved in order to obtain a thorough understanding of the problem. The modeling effort also focuses on understanding the experimentally-observed hysteresis associated with a cyclic moment versus rotation response, as well as the development of simple analytical models which can approximately describe the structural response of a typical torsional spring.