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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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6 results
Now showing 1 - 6 of 6
- 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. - PublicationMechanical properties of abnormal human aortic and mitral valves(01-01-2011)
;Paranjothi, K.; ;KrishnaKumar, R.Balakrishnan, K. R.Details about custom built experimental set up to perform uniaxial and biaxial tests on planar soft tissues are presented. This displacement controlled set up can apply and measure loads ranging up to 100 N. The surface deformation is determined from tracking markers in 3D space using 2 CCD cameras. Discarded valve tissue from patients undergoing valve replacement surgery were collected and stored at 4°C in normal saline and experiments were completed within 24 hours from harvest. Uniaxial tests on aortic valve leaflets and biaxial tests on mitral valve leaflets were conducted. Results show that the deformation of these tissues is not homogeneous. The principal stretches in the plane orthogonal to the direction of stretching in the uniaxial stretch experiment are not the same but the principal directions do not change much with loading. Further, the results show that both the valve leaflets are compressible. The loading and unloading path is nearly the same and is not sensitive to the rate of displacement when it is varied between 200μm/s and 800μm/s. These results have implications in the development of constitutive models for these tissues. - PublicationMechanical properties of human saphenous vein(01-01-2011)
;Paranjothi, K.; ;KrishnaKumar, R.Balakrishnan, K. R.Details about custom built experimental set up to perform inflation tests at constant length on blood vessels are presented. Using this displacement controlled set up we can apply and measure pressures up to 100 kPa and axial loads ranging up to 100 N. The surface deformation is determined from tracking twelve markers in 3D space using 2 CCD cameras. Discarded vein tissue from patients undergoing Coronary bypass surgery were collected and stored at 4°C in normal saline and experiments were completed within 24 hours from harvest. Inflation tests at different axial stretch ratios on saphenous vein were conducted. Results show that the deformation of the vein is not axially symmetric. These suggest that the vein is inhomogeneous and/or residually stressed not only in the radial direction, but also in the circumferential and/or axial direction. The loading and unloading path is not different, suggesting that the vein is being subjected to non-dissipative process. Checking for the incompressibility condition, results show that the vein is compressible. These results have implications in the development of constitutive models for the vein. - PublicationIssues related to measurement of dynamic modulus of bituminous mixtures(01-01-2016)
;Deepa, S.; Murali Krishnan, J.The AASHTO: TP 79-10 standard stipulates the test procedure for the measurement of dynamic modulus of bituminous mixtures. In this investigation, dynamic modulus data of two types of bituminous concrete mixtures (an unmodified binder and crumb rubber modified binder) are studied using TP-79-10 protocol. The experiments showed that the total strain decreased with time at higher temperatures and at lower frequencies. Also, for some mixtures, the phase lag decreased with decreasing frequency. While many studies reported such observations, these anomalous results are normally ascribed to the errors in measurement mechanisms and have not been explained within the context of the material behavior. Here it is shown that Burgers' viscoelastic model exhibits these phenomena. Also, the need for data processing techniques using the complete loading history and a viscoelastic model is emphasized. - PublicationExperiments to find constitutive relation for materials undergoing large deformation(01-12-2010)
;Hariharaputhiran, H.In this article, details about state of art custom built experimental set up to perform biaxial tests on thin sheets made of polymers or soft biological tissues is presented. This displacement controlled set up can apply and measure loads ranging from 0.01 N to 100 N. Then, the uniform or non-uniform surface deformation is determined from tracking a set of markers in 3D space using 2 CCD cameras. Using this setup both elastic and viscoelastic properties of the material could be characterized and the assumption of incompressibility verified. Following Rivlin and Saunders,1 the stored energy corresponding to vulcanized rubber, for stretch ratios less than 1.5, is found by systematically varying one of the variables in the stored energy function. This is achieved by performing biaxial extension tests in which the stretch ratio along one direction is held constant but varied between protocols and the stretch ratio in the perpendicular direction is increased gradually from 1 to 1.5. Then, the predictive capability of the stored energy function is examined by comparing its prediction for the uniaxial extension test with the actual experimental results. However, unlike Rivlin and Saunders, the stored energy is allowed to be either a function of the invariants of left Cauchy-Green stretch tensor (Rivlin2) or the invariants of Hencky strain (Criscione et al3) or the principal stretch ratios (Ogden4). None of the stored energy functions evaluated in this study is able to consistently predict the available experimental data. © 2010 SPIE. - PublicationCriticality of Cracks in Rails Using Photoelasticity and Finite Elements(2024-01-01)
;Ramaswamy, Ganesh ;Verma, Naman; Welded rails are widely used in the railway industry nowadays for better performance over jointed rails. Cracks initiate in these rails during service increasing its vulnerability to failure in adverse thermal gradients. It is desirable to study the adverse cases using simplified models to get meaningful insights for prototype analysis. Toward this, photoelastic experiments are carried out on simplified planar models for certain crack configurations in tension and compression zones under contact loading. The stress intensity factors (SIFs) are evaluated using over-deterministic nonlinear least squares method. The same cases are numerically simulated using Abaqus® and compared with experimental results for validation. Configurations are identified for their criticality based on the evaluated SIFs. A symmetrically loaded bottom crack configuration is taken first to gauge the difference in numerical and experimental SIFs. Next, for two different configurations with same load, it is noted that crack in the compression zone shows higher SIF compared to that in tension zone. It is shown that the numerical results match with experiments for crack in compression zone when it is remodelled as a crack with a finite root radius. This study finds application in rail-fracture analysis considering multiple crack interactions.