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Saravanan Umakanthan
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Saravanan Umakanthan
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Saravanan Umakanthan
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Saravanan, Umakanthan
Sarvanan, U.
Saravanan, U.
Umakanthan, S.
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13 results
Now showing 1 - 10 of 13
- PublicationNon-linear modeling of the influence of rest period on healing behavior of asphalt concrete mixtures(01-01-2022)
;Roy, N. ;Chowdary, V.; Krishnan, J. M.Realistic traffic conditions involve random load amplitude, frequency (speed) and rest periods between load applications. Out of these three factors, one factor which can be controlled and which can throw light on the viscoelastic response of the asphalt concrete mixtures and to some extent on the “healing” nature of these materials is rest period between loadings. An experimental investigation was designed to study the behavior of asphalt concrete mixture during the rest period of a creep and recovery test by providing a prolonged rest period between each set of 100 test cycles. The test was carried out in the unconfined and confined condition, at temperatures of 20, 40 and 55°C. During rest periods, the confinement pressure was maintained in the material. It was observed that during the rest period, the material attained a beneficial internal structural state that required a lesser time to reach a ‘stable’ state when loaded afterwards. It was noted that confinement pressure was necessary for assisting the healing of the material. To model this response of the material, a non-linear upper convected Burgers’ model was used. The model parameters could explain the material behavior and the conditions under which any beneficial internal structural changes happen in the material. - PublicationNumerical techniques for solving truss problems involving viscoelastic materials(01-06-2020)
;Ananthapadmanabhan, S.We develop a methodology for solving truss problems involving viscoelastic materials where, of all the member forces that satisfy the nodal force equilibrium equation and nodal displacements that satisfy the displacement boundary conditions, those member forces and nodal displacements that satisfy the constitutive relation are sought. Since a rate type viscoelastic constitutive relation involves the rate of the stress or strain, this study explores the use of member forces, nodal displacements, and support reactions or their rates as independent variables. Assuming small deformations, the nodal force equilibrium and the displacement boundary condition results in a linear equality constraint between the independent variables. Then we find the unknown independent variables such that the root mean squared error in the constitutive relation of the members of the truss is minimized subject to the satisfaction of the linear constraint at selected times. The objective function is evaluated at selected times or integrated over subintervals of time. We explore six possible solution methods and benchmark them for their accuracy and efficiency. We study statically determinate and indeterminate truss whose members are modeled using rate and integral type viscoelastic constitutive relations for creep and oscillatory loading. For the standard linear solid model, we find that the proposed methods are more accurate than ABAQUS and, at times, require lesser computational wall time. We also demonstrate the applicability of the proposed methodology to fractional order and nonlinear viscoelastic constitutive relations. - PublicationMulti-field formulations for solving plane problems involving viscoelastic constitutive relations(01-03-2023)
;Ananthapadmanabhan, S.This article reports a multi-field numerical formulation for solving plane problems involving viscoelastic materials. Stress fields satisfying equilibrium equations are constructed using Airy's potentials which are expressed as a linear combination of C2 basis functions. The strain field is derived from a continuous displacement field obtained from a linear combination of C0 basis functions. An appropriate linear combination of these stress and displacement basis functions is determined such that the resulting stress and strain fields satisfy the constitutive relation subjected to the satisfaction of the constraints arising from the boundary conditions. Since a viscoelastic constitutive relation involves stress, strain, and their rates, stress and displacement degrees of freedom or their rates can be considered as optimization variables for minimizing the error in satisfying the constitutive relation. Two Algorithms are proposed based on this choice of optimization variable. Accuracy and efficiency of the proposed algorithms are studied through five different boundary value problems involving four forms of the viscoelastic constitutive relations and for two loading histories. Using the developed rectangular element, viscoelastic beam bending problem is solved for the different constitutive relations studied. - PublicationOn accurate measurement of non-uniform displacement gradient(01-01-2023)
;Kumar, PratyushCommonly, the displacement gradient is measured, assuming its variation to be uniform. Systematic error arising due to local uniform approximation of non-uniform displacement gradient is investigated for in-plane periodical varying displacement gradient through the Taylor method. The Taylor method's calculated bound is loose and at variance with the experimental observations. Consequently, an alternate error bound, based on Fourier representation, is proposed, which yields a tighter bound and provides the explanation for the experimental observations. The analytical results are verified through experimental investigation on a plain concrete cylinder subjected to uniaxial compression. The most significant findings are (1) for a body exhibiting periodically varying displacement gradient, the strain measurement would be repeatable for gauge length at least twice the displacement gradient periodicity but would have significant error, and (2) orthogonal gauge orientation (0–45–90 rosette) renders more accurate strain measurement than skewed arrangement (0–60–120 rosette). - PublicationExperimental and analytical studies on shrinkage and creep behavior of RC walls and prisms(01-01-2023)
;Shariff, Mohammad Najeeb; A component level experimental study has been carried out on four reinforced concrete (RC) walls subjected to a sustained compressive load for a period of 1 year and shrinkage tests on 10 prisms under ambient environmental conditions. Two extreme longitudinal reinforcement percentages and two grades of concrete were considered and their influence on the time-dependent behavior studied. It was observed that both longitudinal percentage of steel and concrete grade have a significant influence on the time-dependent strains. The evolution of time-dependent strain in RC member was also predicted, adequately accounting for the effect of reinforcement, using a theoretical model which can employ any linear viscoelastic constitutive law for concrete and a linear elastic constitutive law for reinforcing steel. The ACI 209 and fib MC 10 recommendations for creep and shrinkage of plain concrete have been used for the prediction of long-term strains. It is demonstrated that the analysis predicts the time-dependent strains reasonably well (with a statistical mean deviation error of 1.16 and 1.00) for the creep tests on RC walls, when the compliance function proposed by ACI and fib is used. However, in the case of shrinkage tests, the accuracy with both ACI and fib models was limited (1.64 and 1.66, respectively). It is further demonstrated that by suitably recalibrating the compliance and shrinkage parameters in both ACI and fib models, the accuracy of shrinkage prediction in the companion RC specimens improves significantly with mean deviation error of 1.07 and 1.05 for ACI and fib models, respectively. - PublicationTime-Dependent Strains in Axially Loaded Reinforced Concrete Columns(01-08-2020)
;Shariff, Mohammad Najeeb; Time-dependent strains in reinforced concrete (RC) members are usually estimated using approximate algebraic methods. This paper presents an exact method for estimating the time-dependent strains in RC members subjected to concentric axial compression, using creep compliance and shrinkage strain information for the corresponding plain concrete. The axial strain in concrete is taken to be the sum of shrinkage strain and the creep strain. Shrinkage strain in concrete is modeled as a: "lack-of-fit" problem. Assuming a linear viscoelastic constitutive law for concrete and a linear elastic constitutive relation for reinforcing steel, the corresponding one-dimensional viscoelastic boundary value problem is solved. It is assumed that there is a perfect bond between concrete and steel. The proposed method is validated using tests reported in the literature. The prediction of overall time-dependent axial strains under applied axial loads is found to match the observed test results closely. However, there are discrepancies in the relative magnitudes of creep and shrinkage strains, and the possible reasons for these are also discussed. - PublicationA methodology for post-processing the four-point beam bending data and computing stiffness modulus using harmonic analysis(08-09-2023)
;Sasidharan, Deepa; Krishnan, J. MuraliThe computation of modulus of bituminous mixes from a beam bending test conforming to an undamaged yet steady state is not straightforward. The most widely used practice of choosing the 50th or 100th cycle, for modulus computation, does not ensure that the material response has reached a steady state, crossing the initial transient stage of drastic modulus reduction. In the current study, it is analytically shown that the material retardation time governs the attainment of a steady state response. The study proposes a methodology for post-processing the four-point beam bending test data so as to identify the cycles that could result in a sensible computation of material modulus. The experimental investigations involve four-point beam bending (4-PB) tests carried out on four bituminous mixes, prepared using an unmodified and three modified binders. The 4-PB tests are carried out at 20 oC, 10 Hz frequency at strain levels of 200, 400, 600 and 800 micro-strains. The harmonics of the input/output waveform has been used to identify the cycles that can be used for the computation of a material modulus, and the modulus is computed from the Lissajous plots (stress–strain plots) of the cycles prior to damage initiation. Based on harmonic analysis, the current study specifies a range of modulus for each mix at various strain levels, and the values are further compared with the modulus computed using the conventional post-processing procedure. It is observed that the conventional procedure of using the stiffness modulus at 100th cycle results in higher values of modulus than the ones computed using the proposed post-processing method, as a consequence of the transient response of the material before attaining a steady state. - PublicationModeling the non-dissipative response of vulcanized unfilled rubber(01-03-2020)
;Gokulnath, C.Here the possibility of developing a better three dimensional model for rubber when Hencky strain is written as an explicit function of the Cauchy stress is examined. Based on the experimental evidence, vulcanized unfilled rubber is assumed to be isotropic, incompressible, and deforming from a stress-free reference configuration. Vulcanized unfilled rubber undergoes strain-induced crystallization when uniaxial stretch exceeds 2. Therefore, in this study, a non-dissipative model is sought for rubber only till the von Mises stress is below a critical value. Using the biaxial response reported in Kawabata et al. (1981), the material functions are arrived adopting Rivlin and Saunders methodology. The material constants in the determined material functions are found using biaxial tests for four other experimental studies on rubber reported in the literature. The ability of the arrived constitutive model to describe the uniaxial and equal biaxial response of the same rubber is evaluated. The proposed model is benchmarked with established models in the classical framework. Among the models studied the proposed model performed as well as the other models for Kawabata et al. data set and marginally better than the other models for the remaining four experimental data sets. However, while the proposed model performance does not critically depend on the experiments used to deduce the material parameters, for the other models the material parameters need to be found from fixed biaxial experiments for better performance. - PublicationFeasibility on accurate measurement of non-uniform strain field through contact methods(01-09-2021)
;Kumar, PratyushWhen straight material filaments do not remain straight after deformation, the strain varies spatially. These spatially varying strain fields arise because of (1) non-uniform distribution of boundary traction, (2) presence of residual stress in the reference configuration, (3) the body being inhomogeneous. The strain measured using devices such as extensometer and strain gauge assumes that the strain is uniform over the gauge length, irrespective of the strains actual variation. Here the accuracy of the strain estimated using contact strain measurement techniques is investigated by assuming that the uniaxial strain (not stress) varies periodically along the measurement axis. A tight bound for the error in the measured strain is obtained and verified through numerical simulation. This study's significant finding is that for gauge length of strain measurement about two times the periodicity of the strain variation, the measured strain's value would be repeatable but with a significant error. Thus, one has to be cautious about the magnitude of the estimated non-uniform strain. - PublicationFinite element formulation for implicit magnetostrictive constitutive relations(01-12-2020)
;Sudersan, S.; Arockiarajan, A.Magnetostrictive materials that couple mechanical and magnetic domains have been widely explored for use in sensors and actuators. These materials often exhibit a nonlinear material response under applied magnetic fields, which limits the use of linear constitutive models. Furthermore, the nonlinear constitutive relations tend to be implicit in nature. Hence, a finite element scheme that can handle the implicit relationship between the mechanical (stresses and strains) and magnetic (magnetic flux density and magnetic field) quantities is proposed in order to arrive at solutions to boundary value problems. In the proposed scheme, while the physical requirements of equilibrium and strain–displacement relation are satisfied point-wise, the constitutive relations hold in a weak integral sense. A fully coupled magnetostrictive plane stress rectangular element is developed based on the proposed scheme and its efficacy in arriving at solutions to coupled field boundary value problems is illustrated by subjecting the element to standard loading conditions.