Department of Mechanical Engineering

&ldquo;IIT Jodhpur is committed to impart quality education to facilitate the creation of qualified, competent and responsible human resources to meet the emerging technological challenges of the world. It is working towards creating an equitable learning platform that is positive, accessible and effective in the face of the modern societal and scientific advancements.

Flexibility in curriculum, in all its academic programs, encompassing elements of teaching, research, creativity, innovation and entrepreneurship is the most unique feature of IIT Jodhpur. The Department of Science and Technology (DST), under the National Mission on Cyber Physical Systems, has identified IIT Jodhpur as a Technology &amp; Innovation Hub in the area of Augmented Reality and Virtual Reality. The institute has also been nominated as the coordinator for the Jodhpur City and Knowledge Cluster by the Office of Principal Scientific Adviser, Government of India.

The sprawling 852-acre IIT Jodhpur campus is a majestic tribute to the deep-rooted diverse cultural heritage of the region. The campus is an architectural masterpiece, which is slated to become an international exemplar of sustainability with net-zero energy, and advanced water and waste management strategies.&rdquo;

IIT Jodhpur

A set of nonlinear electrothermoelastic constitutive relations was derived to represent the electric hysteresis effects in a piezomaterial by following a consistent thremodynamic formulation. The field of smart structures has got great importance in the field of research with the development of piezoceramic sensors and actuators of different shapes and sizes for the use in structural applications. Piezomaterials has showed polarization-electric (P-E) field hysteretic losses under cyclic variation of the applied electric field. It was observed that the area of the P-E hysteresis loop decreases with an increasing compressive preload. Experimental data showed that as the preloading increases, the remnant polarization shows a reduction in magnitude.The nonlinear electrothermoelastic formulation can also be easily integrated in the structural dynamic analysis of smart structures with embedded piezoactuators and sensors.

World University root node

AIAA Journal

Thermodynamic modeling of hysteresis effects in piezoceramics for application to smart structures

In this present work, the non-linear behavior of a single-link flexible visco-elastic Cartesian manipulator is studied. The temporal equation of motion with complex coefficients of the system is obtained by using D'Alembert's principle and generalized Galarkin method. The temporal equation of motion contains non-linear geometric and inertia terms with forced and non-linear parametric excitations. It may also be found that linear and non-linear damping terms originated from the geometry of the large deformation of the system exist in this equation of motion. Method of multiple scales is used to determine the approximate solution of the complex temporal equation of motion and to study the stability and bifurcation of the system. The response obtained using method of multiple scales are compared with those obtained by numerically solving the temporal equation of motion and are found to be in good agreement. The response curves obtained using viscoelastic beams are compared with those obtained from a linear Kelvin-Voigt model and also with an equivalent elastic beam. The effect of the material loss factor, amplitude of base excitation, and mass ratio on the steady state responses for both simple and subharmonic resonance conditions are investigated. © 2008 Elsevier Ltd. All rights reserved.

International Journal of Non-Linear Mechanics

Non-linear vibration of a single link viscoelastic Cartesian manipulator

We study natural convection driven by unstable concentration differences of sodium chloride (NaCl) across a horizontal permeable membrane at Rayleigh numbers (Ra) of 1010 to 1011 and Schmidt number (Sc) = 600. A layer of brine lies over a layer of distilled water, separated by the membrane, in square-cross-section tanks. The membrane is permeable enough to allow a small flow across it at higher driving potentials. Based on the predominant mode of transport across the membrane, three regimes of convection, namely an advection regime, a diffusion regime and a combined regime, are identified. The near-membrane flow in all the regimes consists of sheet plumes formed from the unstable layers of fluid near the membrane. In the advection regime observed at higher concentration differences (ΔC) across the membrane, there is a slow overturning through-flow across the membrane; the transport across the membrane occurs mostly by advection. This phenomenology explains the observed Nub ∼ Ra2/Sc scaling of the Nusselt number. The planforms of sheet plumes near the membrane show a dendritic structure due to the combined influence of the mean shear due to the large-scale flow and the entrainment flow of the adjacent plumes. The near-membrane dynamics show initiation, elongation and merger of plumes; a movie is available with the online version of the paper. Increase in Ra results in a larger number of closely and regularly spaced sheet plumes. The mean plume spacing in the advection regime λb, is larger than the mean plume spacing in Rayleigh-Bénard convection (λ), and shows a different Ra-dependence. The plume spacings in the advection regime (λb) show a common log-normal probability density function at all Ra. We propose a phenomenology which predicts λb ∼ √ZwZVi, where Zw and ZVi are, respectively, the near-wall length scales in Rayleigh-Bénard convection (RBC) and due to the advection velocity. In the combined regime, which occurs at intermediate values of ΔC, the flux scales as (ΔC/2)4/3. At lower driving potentials, in the diffusion regime, the flux scaling is similar to that in turbulent RBC. © 2008 Cambridge University Press.

Journal of Fluid Mechanics

Convection due to an unstable density difference across a permeable membrane

The present paper investigates the effect of two variables, namely direction of parameterization and cutter diameter on process geometry, cutting forces, and surface error in peripheral milling of curved geometries. In machining of curved geometries where the curvature varies continuously along tool path, the process geometry variables, namely feed per tooth, engagement angle, and maximum undeformed chip thickness too vary along tool path. These variations will be different when a given geometry is machined from different parametric directions and with different cutter diameters. This difference in process geometry variations result in changed cutting forces and surface error along machined path. This aspect has been studied for variable curvature geometries by machining from both parametric directions and using cutters of different diameter. The computer simulation studies carried out show considerable amount of shift in the location of peak cutting forces with the change in cutting direction and cutter diameter, particularly in concave regions of workpiece geometry. A new parameter γ that relates the instantaneous curvature of workpiece with cutter radius is defined. The larger value of γ is an indicator of greater shift in the location of peak forces from the point of maximum curvature on the workpiece. The simulation results are validated by carrying out machining experiments with curved workpiece geometry and are found to be in good agreement. © 2007 Elsevier Ltd. All rights reserved.

International Journal of Machine Tools and Manufacture

Effect of direction of parameterization on cutting forces and surface error in machining curved geometries

Continuum level modeling of damage is a complex problem because of existence of several failure mechanisms at various length-scales, e.g., matrix crack, interfacial crack and delamination. Several macroscopic models have been proposed in the literature for the characterization of the influence of these damage modes. However, very few models account for the micro-level mechanisms. Further, most micromechanical models are two-dimensional (2D) in nature. Hence, the effect of finite size and orientation of the damage is not captured. The present work focuses on developing a generalized macro level damage model for unidirectional composites based on the micromechanical analysis in the presence of finite sized damages. The effect of microdamage mechanisms is modeled through effective stiffness reduction at a macro point. A series of numerical experiments, based on the mathematical theory of homogenization, have been conducted at the level of the constituents to obtain the effective stiffness properties for the Representative Volume Element (RVE) with existing damage. The effect of various damage mechanisms, size and mode of damage on effective macro properties is studied and definitive conclusions are drawn. The dependency of these effects on the volume fraction is also studied. Based on the conclusions, a generalized macro level damage model is proposed. © 2008 Trans Tech Publications.

Advanced Materials Research

Towards a generalized macro-level damage model for unidirectional composites

In the present paper continuum damage based meso-model proposed by Ladvèze is used to predict the response of initially damaged laminated composites. The model is based on three foundations of meso-model, internal variable approach and method of local state. The present model is refined by replacing the interface as a very thin layer of resin. Further, this layer uses higher order approximation in transverse direction for displacement field over linear variation used in original model. This model has been implemented in the generalized layerwise and and region-by-region finite element models developed by authors. It is seen that the fibre failure mode is dominant comapared to other failure modes in giving significant difference in transverse displacement signature profiling whereas the delamination mode has weak effect. The in-plane strains also show similar behaviour. Here, the results are presented for different shapes and sizes of damage under the transverse load only. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference

Static damage surface signatures for laminated composite plates

This paper presents the settlement analysis of a beam resting on geosynthetic reinforced granular fill-soft soil system. Each subsystem of the reinforced fill-soil system is idealized by elastic membrane, Pasternak shear layer, Winkler springs and dashpots, as applicable. The suggested model incorporates various aspects of the behavior of the geosynthetic-reinforced granular fill-soft soil system such as horizontal stress induced in the granular fill, the compressibility of the granular fill, and the time-dependent behavior of the subgrade. The differential equations governing the settlement response of the beam resting on two layered reinforced foundation soil has been formulated by incorporating deformation compatibility conditions. The numerical solutions are obtained using Finite Element Method and results are presented in non-dimensional form. The parametric studies are carried out to enumerate the effects of parameters on the settlement response of the system. Results indicate that over a large number of various parameters under large deformation the proposed model evaluate the settlement of the system and horizontal displacement of membrane with reasonable accuracy. It is observed that compressibility, shear modulus and thickness of granular fill, pre-stressing and tension modulus of reinforcement have appreciable influence on the settlement of the system and horizontal displacement of membrane. It is observed that the horizontal displacement of the geosynthetic membrane is negligible as compared to that of the vertical settlement. The model is also analyzed for the case of a sand drain in the soft soil which indicated that the elapsed time and the radius of the sand drain significantly affects the settlement response of the system.

12th International Conference on Computer Methods and Advances in Geomechanics 2008

A finite element study of beam on reinforced granular beds with sand drains

Electric field-polarization interaction shows nonlinear effects in the constitutive relations. In this study, an attempt is made to include these interaction effects in the finite element formulation. A layer-by-layer finite element code is developed to handle the linear and nonlinear problems. Linear and nonlinear analysis is carried out for a smart plate with surfacemounted distributed piezo layer. The nonlinearity leads to a significant increase in the transverse deformation. © 2008 Trans Tech Publications.

Layer-by-layer finite element analysis of smart composite plates

Several plate models have been proposed in the literature for the analysis of laminated plates. These are based either on an equivalent through-thickness formulation or a layerwise formulation. It is shown in the literature that while the equivalent models are economical, the layerwise models are expensive but are also more accurate, especially with respect to the transverse stresses. Generally, the same model is used throughout the domain. The current study addresses the issue of economical and accurate computation of local stresses, strains and displacements (as well as global quantities) using combinations of layerwise, equivalent or intermediate models in various regions of the domain. A region-by-region modeling strategy is presented for a chosen general family of equivalent, intermediate and layerwise models. The proposed strategy allows the user to put any model (of any order in the thickness direction) in any desired region of interest. The effectiveness of the strategy is demonstrated through numerical examples. It is shown that this approach can significantly reduce computational cost and can also lead to good resolution of the local stress and displacement fields for domains with unsymmetric laminae, cut-outs, local damage, corner edges, sudden transition of boundary conditions and material. © 2007 Elsevier Ltd. All rights reserved.

Computers and Structures

Region-by-region modeling of laminated composite plates

A generalized stochastic buckling analysis of laminated composite plates, with and without centrally located circular cutouts having random material properties, is presented under uniaxial compressive loading. In this analysis, the layerwise plate model is used to solve both prebuckling and buckling problems. The stochastic analysis is done based on mean centered first-order perturbation technique. The mean buckling strength of composite plates is validated with results available in the literature. It has been observed that the present analysis can predict buckling load accurately even for plates with large cutouts. Micromechanics based approach is used to study the effect of variation in microlevel constituents on the effective macrolevel properties like elastic moduli. Consequently, the effect of uncertainty in these material properties on the buckling strength of the laminated plates is studied. Parametric studies are carried out to see the effect of hole size, layups, and boundary conditions on the mean and variance of plate buckling strength. Copyright © 2007 by ASME.