Faculty Publications
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Publications by NITK Faculty
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Item Case study for contact pressure improvisation with graded implant material in articular cartilages of knee joint(Korean Society of Mechanical Engineers, 2021) Raju, V.; Koorata, P.K.; Kamat, Y.In this study, the effect of graded design in comparison to homogeneous cartilage material is investigated for contact pressure distribution in the human knee joint. Knee implants are assumed a homogeneous material. In reality, cartilages are not homogeneous, and to replicate the heterogeneity of cartilages, a graded design is proposed. Simulation results show improved contact pressure distribution in the knee joint due to the graded composition of cartilages. The results are helpful in designing a new class of implant materials. © 2021, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature.Item Numerical investigation on the sensitivity of endplate design and gas diffusion material models in quantifying localized interface and bulk electrical resistance(Elsevier Ltd, 2021) Shinde, U.; Koorata, P.K.A localized non-intuitive relationship between electrical interface contact resistance and bulk properties such as bulk electrical resistance and permeability in the fuel cell gas diffusion layer (GDL) is reported. A numerical method is adopted to investigate contact pressure and hence the interface contact resistance at the interfaces of bipolar plate (BPP)|GDL and GDL|Polymer electrolyte membrane (PEM). The results are observed to be sensitive to GDL material models as well as endplate designs. This means, endplates designed to improve the electrical contact resistance or contact pressure at the BPP|GDL interface may not necessarily assure an improvement in bulk properties, in fact, it is observed in this study that these properties are inversely related. Further, a differential deformation in GDL along with consolidation effect is predicted with compressible version of hyperelastic material model. More importantly, it is revealed that the selection of material models plays a significant role in the deformation behaviour of the GDLs irrespective of the clamping design adopted. © 2021 Hydrogen Energy Publications LLCItem Computational evaluation of the effect of femoral component curvature on the mechanical response of the UHMWPE tibial insert in total knee replacement implants(Elsevier Ltd, 2022) Raju, V.; Koorata, P.K.Total knee replacement (TKR) surgery is done on individuals with end-stage osteoarthritis to restore knee function and alleviate joint discomfort. There have been recent developments in the design of customized implants based on patient-specific data obtained from MRI scans and subsequent image processing techniques. Here curvature of the femoral component plays an important role in effective implant design. Therefore, the objective here is to investigate the influence of this curvature of the femoral component on the mechanical response of the bearing component. A 3D finite element knee implant model with a circular and an elliptical femoral component is developed and investigated for gait kinetics and kinematics. Responses such as contact pressure, stresses, strains, and wear produced on the tibial insert are estimated throughout the gait cycle. These findings suggest that the elliptical femoral component generates less contact pressure on the tibial insert than its circular counterpart. It is also inferred that too much variation in this curvature is not recommended as it may affect the patient's comfort level. In addition, the wear of the tibial insert is computed based on the contact pressure created by both knee implant models. Our study suggests an optimum value for the curvature and the comfort level of the patients over the existing knee implant designs. © 2022 Elsevier Ltd. All rights reserved.Item Influence of material heterogeneity on the mechanical response of articulated cartilages in a knee joint(SAGE Publications Ltd, 2022) Raju, V.; Koorata, P.K.Structurally, the articular cartilages are heterogeneous owing to nonuniform distribution and orientation of its constituents. The oversimplification of this soft tissue as a homogeneous material is generally considered in the simulation domain to estimate contact pressure along with other physical responses. Hence, there is a need for investigating knee cartilages for their actual response to external stimuli. In this article, impact of material and geometrical heterogeneity of the cartilage is resolved using well known material models. The findings are compared with conventional homogeneous models. The results indicate vital differences in contact pressure distribution and tissue deformation. Further, this study paves way for standardizing material models to extract maximum information possible for investigating knee mechanics with variable geometry and case specific parameters. © IMechE 2022.Item Computational assessment on the impact of collagen fiber orientation in cartilages on healthy and arthritic knee kinetics/kinematics(Elsevier Ltd, 2023) Raju, V.; Koorata, P.K.Background: The inhomogeneous distribution of collagen fiber in cartilage can substantially influence the knee kinematics. This becomes vital for understanding the mechanical response of soft tissues, and cartilage deterioration including osteoarthritis (OA). Though the conventional computational models consider geometrical heterogeneity along with fiber reinforcements in the cartilage model as material heterogeneity, the influence of fiber orientation on knee kinetics and kinematics is not fully explored. This work examines how the collagen fiber orientation in the cartilage affects the healthy (intact knee) and arthritic knee response over multiple gait activities like running and walking. Methods: A 3D finite element knee joint model is used to compute the articular cartilage response during the gait cycle. A fiber-reinforced porous hyper elastic (FRPHE) material is used to model the soft tissue. A split-line pattern is used to implement the fiber orientation in femoral and tibial cartilage. Four distinct intact cartilage models and three OA models are simulated to assess the impact of the orientation of collagen fibers in a depth wise direction. The cartilage models with fibers oriented in parallel, perpendicular, and inclined to the articular surface are investigated for multiple knee kinematics and kinetics. Findings: The comparison of models with fiber orientation parallel to articulating surface for walking and running gait has the highest elastic stress and fluid pressure compared with inclined and perpendicular fiber-oriented models. Also, the maximum contact pressure is observed to be higher in the case of intact models during the walking cycle than for OA models. In contrast, the maximum contact pressure is higher during running in OA models than in intact models. Additionally, parallel-oriented models produce higher maximum stresses and fluid pressure for walking and running gait than proximal-distal-oriented models. Interestingly, during the walking cycle, the maximum contact pressure with intact models is approximately three times higher than on OA models. In contrast, the OA models exhibit higher contact pressure during the running cycle. Interpretation: Overall, the study indicates that collagen orientation is crucial for tissue responsiveness. This investigation provides insights into the development of tailored implants. © 2023 IPEMItem Soil-structure Interaction Effects on Tall Industrial Chimney Subjected to Along-wind Load(International Association of Engineers, 2025) Sandeep, G.S.; Arun Kumar, Y.M.; Pandit, P.; Jayalekshmi, B.R.The present study focuses on the soil-structure interaction (SSI) effects on tall industrial chimneys subjected to along-wind loading. The influence of soil flexibility because of soil-structure interaction significantly affects the dynamic behavior and wind-induced vibrations of tall structures subjected to wind loads. A 3D finite element (FE) model has been developed to represent the integrated system comprising of chimney structure, annular raft foundation, and supporting soil. The model accounts for both self-weight and along-wind load, enabling a comprehensive assessment of the system’s response. The analysis specifically aims to evaluate the vertical displacement of a raft, contact pressure distribution beneath the raft, bending moment distribution within annular raft foundation, and modal analysis of the chimney. Two different SSI approaches, the Winkler foundation model and the Elastic Continuum model (a more refined and realistic model), have been employed. Their results are compared with those from the conventional (non-interactive) method, which typically assumes a rigid base or ignores soil flexibility. The findings indicate that the inclusion of SSI, particularly using the Winkler and the Elastic Continuum approaches, leads to a notable reduction in bending moments in the raft foundation as compared to the conventional method. This reduction is attributed to the redistribution of stress and the flexibility of the supporting soil, which allows for a more realistic representation of how the foundation interacts with the underlying soil. © 2025, International Association of Engineers. All rights reserved.Item Effect of Humidity and Temperature on PVD TiAlN-Coating Wear(Springer, 2025) Cadambi, S.; Dasari, B.P.; Jayaram, V.Gas turbine blades and disks undergo wear at high temperatures at dovetail joints where tolerances are very small. Thin hard coatings are known to enhance the wear resistance of the superalloy components minimally influencing the tolerance levels. However, fundamental understanding of the coating’s wear mechanisms operating in these harsh conditions is not well understood. In this study, wear tests are performed to understand the wear mechanisms that operate in the temperature range from RT up to 800 °C for thin hard TiAlN coating using simple wear geometry eliminating any influence of wear debris. It is challenging to measure wear of thin hard coatings especially at elevated temperatures but important nevertheless. A coated ball on disk geometry with rough alumina as counterface is used for wear studies to understand exclusively the influence of humidity and temperature coating wear behavior. Cathodic arc evaporation, a physical vapor deposition technique is used to deposit TiAlN coatings on heat-treated IN718 substrates and characterized with, XRD, EPMA, TEM, SEM, nanoindentation, and FIB. The wear at room temperature shows scatter which has been ascribed to seasonal fluctuations in relative humidity. Further, wear results are shown to correlate with Young’s equation for capillary condensation. Wear below 50 pct RH is essentially dry and constant up to 600 °C above which wear increases marginally upto 800 °C. The coefficient of friction shows a maximum at 400 °C, below which friction reduces due to increased adsorption of water vapor, while above 400 °C, TiO2 forms on the surface to reduce the friction. The wear rate at 3 N load in the range of 50–800 °C is ~ 1 × 10?6 mm3/m/N. For 5 N load, the wear rate is same as for 3 N load upto 600 °C but doubles above 700 °C. The average contact pressure through the test is ~ 550 and 650 MPa which is almost twice the design contact pressure. The wear debris gets richer in Ti with increase in temperatures. The Al-rich TiAlN coatings deposited by cathodic arc evaporation (CAE) technique show a low and constant wear behavior over a wide range of temperatures and are ideally suited for the protecting the dovetail joints in gas turbines. © The Minerals, Metals & Materials Society and ASM International 2024.