Faculty Publications
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Item Impact Energy Estimation of AISI304L/AA6063 Alloys Dissimilar Friction Welds Influenced by Various New Faying Surfaces: A Comparative Study(Springer, 2024) Senthil Murugan, S.S.; Paulraj, P.; Kattimani, S.This research paper delves into an innovative approach for enhancing the faying surfaces in the rotary friction welding process. This study evaluates the impact energy in Joule (J) of friction-welded joints (FWJs) between dissimilar cylindrical rods made of AA6063 wrought aluminium and AISI304L austenitic stainless steel focusing on the influence of various faying surface designs and welding parameters. Additionally, the study conducts an in-depth analysis of various faying surface designs. A series of experiments were conducted using a Charpy V-notch tester to analyse 45 different FWJs with diverse surface modifications. Welding conditions such as friction pressure (FP), friction time, and upset pressure were varied to assess their effects on joint toughness. The aim was to utilize the low FP, spanning from 1.2 to 1.8 MPa, in the pursuit of optimizing the welding process. The results revealed notable variations in the impact energy values of FWJs in response to changes in both the faying surfaces of the specimens and the welding parameters. A5 trial achieved the highest impact energy at 38 J. Notably, joints with hemispherical faying surfaces exhibited enhanced toughness, with method N achieving 26 J. Adjustments to the faying surface design and welding conditions had a substantial impact on the toughness and energy absorption of the welded joints. © The Institution of Engineers (India) 2024.Item Performance enhancement in polymer electrolyte membrane fuel cell with flow traps and field gradients: A Numerical Study(Elsevier Ltd, 2024) Padavu, P.; Koorata, P.K.; Kattimani, S.; Gaonkar, D.N.Efficient reactant distribution and water removal are critical during polymer electrolyte fuel cell (PEFC) operation. The bipolar plate and its corresponding flow field design are vital among the PEFC components for enhancing reactant transport and water removal. The issues arising in the PEFC during the high current operation, such as reactant starvation and water removal, can be alleviated by improving the flow channel geometry. In this study, we analyze the variation in overall PEFC performance and corresponding reactant transport phenomenon for two independent design cases. The converging gradient design without channel traps at 0.4 V operating voltage exhibited a current density increment of 6.85% against the conventional design. Moreover, at 0.4 V, including channel traps enhanced the current density, as we observed a current density increment of 7.1% for the converging design with channel traps against the conventional design without channel traps. Likewise, at 0.4 V, the diverging design with channel traps exhibited a current density increment of 5.85% against the diverging design with no channel traps. Further, enhanced reactant distribution is observed in the catalyst layer upon introducing channel traps in the flow field design. © 2024 Hydrogen Energy Publications LLCItem Flutter prediction for unmanned long endurance aircraft using virtual structural model and experimental modes(SAGE Publications Ltd, 2025) Sampath, A.K.; Kattimani, S.Aeroelastic stability is an important consideration in the design and certification processes of modern, flexible aircraft. This includes demonstration of freedom from flutter at all combinations of airspeed and altitude within the flight envelope. This paper presents the analysis and clearance of flutter characteristics for an unmanned medium altitude long endurance aircraft by two distinct methods. The traditional method based on a theoretical Finite Element (FE) model was adopted prior to the conduct of Ground Vibration Tests (GVT) where as the more recent method utilized a Virtual Structural Model (VSM) built on the experimental modal parameters that were obtained from the GVT. The Direct Matrix Abstraction Program (DMAP) feature of MSC NASTRAN was used to create the VSM whose nodes correspond to the GVT accelerometer locations, and to insert the GVT modes into the model. In both approaches the unsteady airloads were generated using the Doublet Lattice Method (DLM). The GVT/VSM based analyses closely mirrored the original FE model analysis and confirmed the existence of sufficient flutter margins, thereby enabling the flight certification of the aircraft. The VSM route to flutter analysis is outlined in this paper as an alternative to using a GVT-tuned FE model. This is beneficial (i) if no FE model is available as it happens with bought out aircraft, or (ii) if the configurations of interest are too few to justify the effort of FE model tuning. © IMechE 2025Item Non-linear transient vibration response of graphene origami enhanced metamaterial beams under spatially-varying temperature distributions(Elsevier Ltd, 2025) Shashiraj; Pitchaimani, J.; Kattimani, S.Understanding the dynamic behavior of advanced materials under varying conditions is crucial for the development of resilient and efficient structural systems. This research investigates the non-linear transient response of auxetic metamaterial beams enhanced with graphene origami under spatially varying non-uniform thermal environment. Using Timoshenko beam theory with von-Kármánn type non-linear strain–displacement relations, graphene origami beams are modeled as layered structures. The equilibrium equations are solved using the Ritz method, with a focus on how different graphene origami distribution patterns, content levels, and folding degrees influence the transient response under various time-dependent forces. Non-linear motion equations are solved using the Newmark-Beta method. This study evaluates the impact of five distinct non-uniform temperature distributions, seven types of time-dependent loadings, three boundary conditions, and three configurations of graphene origami distribution on the vibration characteristics. Results indicate that parabolic temperature distributions with peak temperatures at the beam ends lead to substantially decreased dynamic deflections. This research provides valuable insights into the structural dynamics of graphene origami-enhanced metamaterial beams within complex thermal environments, highlighting the considerable influence of spatial temperature variations along the length of the beam. © 2025