Options
Saravanan Umakanthan
Loading...
Preferred name
Saravanan Umakanthan
Official Name
Saravanan Umakanthan
Alternative Name
Saravanan, Umakanthan
Sarvanan, U.
Saravanan, U.
Umakanthan, S.
Main Affiliation
Email
ORCID
Scopus Author ID
Researcher ID
Google Scholar ID
24 results
Now showing 1 - 10 of 24
- PublicationBiological and mechanical evaluation of a Bio-Hybrid scaffold for autologous valve tissue engineering(01-04-2017)
;Jahnavi, S.; ;Arthi, N. ;Bhuvaneshwar, G. S. ;Kumary, T. V. ;Rajan, S.Verma, R. S.Major challenge in heart valve tissue engineering for paediatric patients is the development of an autologous valve with regenerative capacity. Hybrid tissue engineering approach is recently gaining popularity to design scaffolds with desired biological and mechanical properties that can remodel post implantation. In this study, we fabricated aligned nanofibrous Bio-Hybrid scaffold made of decellularized bovine pericardium: polycaprolactone-chitosan with optimized polymer thickness to yield the desired biological and mechanical properties. CD44+, αSMA+, Vimentin+ and CD105− human valve interstitial cells were isolated and seeded on these Bio-Hybrid scaffolds. Subsequent biological evaluation revealed interstitial cell proliferation with dense extra cellular matrix deposition that indicated the viability for growth and proliferation of seeded cells on the scaffolds. Uniaxial mechanical tests along axial direction showed that the Bio-Hybrid scaffolds has at least 20 times the strength of the native valves and its stiffness is nearly 3 times more than that of native valves. Biaxial and uniaxial mechanical studies on valve interstitial cells cultured Bio-Hybrid scaffolds revealed that the response along the axial and circumferential direction was different, similar to native valves. Overall, our findings suggest that Bio-Hybrid scaffold is a promising material for future development of regenerative heart valve constructs in children. - PublicationAnalysis of the ASTM C512 Spring-Loaded CREEP Frame(01-10-2019)
;Shariff, Mohammad Najeeb; ; Rajagopal, Kumbakonam R.The test method of ASTM C512 (ASTM. 2015. Standard test method for creep of concrete in compression. ASTM C512/C512M. West Conshohocken, PA: ASTM) dictates the use of a spring-loaded creep frame to perform a creep test on concrete. The main thesis of the study is that tests performed using these spring-loaded frames is not a creep test in the sense that the force acting on the specimen is not held constant while the specimen undergoes time-dependent strain. Analysis of this frame is performed using a linear viscoelastic model to represent concrete and isotropic Hooke's law to represent the steel rods and springs. The internal force and displacement in concrete and steel rods at any given instant of time is found using equilibrium equations and compatibility conditions. It is observed that the force transmitted to the concrete does not remain constant throughout the test duration but is a function of the spring and rod stiffness and the viscoelastic properties of the concrete. Hence, a drop in the magnitude of the force transmitted to the concrete specimen occurs in experiments when a spring-loaded creep frame is used. Experimental validation is also carried out by comparing the response of a spring-loaded creep frame with theoretical results. In this work, optimal spring and rod stiffness values to minimize the drop in the force transmitted to the concrete specimen are established. Thus, this study could be used to determine the linear viscoelastic properties of concrete in a creep frame. - PublicationOn the use of linear viscoelastic constitutive relations to model asphalt(01-08-2012)In this article, the appropriateness of modelling asphalt using linear viscoelastic constitutive relations is explored. Towards this, a rate-type nonlinear viscoelastic model recently proposed by Santoshreddy et al. (2011) is used and it is shown that the stress relaxation and creep response of asphalt are influenced by the type of experiment, initial rate of displacement (or loading) and the stress and strain measure used. Furthermore, it is shown that the creep and stress relaxation functions are not dependent functions as required by the linear viscoelastic theory, even in the range of values of engineering strain and stress in which the linearity property holds approximately. These observations lead one to conclude that linear viscoelastic models maybe inappropriate to model asphalt. © 2012 Copyright Taylor and Francis Group, LLC.
- PublicationOn the adequacy of the existing restrictions on the constitutive relations to ensure reasonable elastic response of compressible bodies(03-03-2011)We show that even when the constitutive relations for the elastic response of compressible bodies satisfy the empirical, Baker-Ericksen and ordered forces inequalities and ellipticity restrictions, they could result in physically unrealistic response. We pick a constitutive relation that satisfies the above inequalities and is also globally elliptic but its response to both uniaxial extension and inflation at constant length is physically unrealistic, based on the available experimental observations. However, the Coleman-Noll, pressure-compression, tension-extension and invertibility of force-stretch conditions and that proposed in Carroll and McCarthy (1995) are violated by this constitutive relation. © 2011 Elsevier Ltd. All rights reserved.
- PublicationCharacterization of petroleum pitch using steady shear experiments(01-11-2010)
;Chockalingam, Kanmani; Murali Krishnan, J.Asphalt for highway and runway construction is processed by either air blowing or blending with different petroleum streams. In the blending process, petroleum pitch, a by-product of solvent deasphalting of the vacuum residue is mixed with heavy extract to produce asphalt of the desired specifications. The rheological response of blended asphalt hence depends to a large extent on the constitutive property of petroleum pitch. In an aim to develop robust models for blended asphalt, modeling the mechanical behavior of petroleum pitch hence becomes necessary. In this work reported here, petroleum pitch from crude sources such as Basrah Light, Arab Mix and Arab Light are subjected to steady shear for 99 min at temperatures ranging from 70 to 120 °C for different shear rates. Each of these material exhibited different stress overshoot and decay during steady shear depending on the temperature and shear rate. A viscoelastic fluid model of the rate type is selected to model the response of the material. Using the recent thermodynamic framework based on Gibbs potential proposed by Rajagopal and Srinivasa [27], restrictions on the proposed model are obtained. The rotational flow problem is solved and the material parameters are estimated. The model predictions are corroborated with the experimental observations and they are found to be reasonably good. © 2010 Elsevier Ltd. All rights reserved. - PublicationModeling diffusion and reaction of sulfates with cement concrete using mixture theory(01-03-2018)
;Gouder, ChethanHere mixture theory is used to capture the changes in cement concrete exposed to sodium sulfate till cracks develop. Toward this, the mixture is assumed to be made of eleven constituents of which the sodium sulfate and water move relative to themselves and the remaining nine solid constituents. The nine solid constituents constrained to move together are the eight relevant chemical constituents in concrete that react with sodium sulfate and all the other remaining chemical constituents of concrete that do not react with sulfates. Constitutive assumptions needed to be made within this mixture theory framework are the same as those reported by Gouder and Saravanan (Acta Mech 227(11):3123–3146, 2016). Within this framework of mixture theory, the radial ingress and reaction of sodium sulfate solution with the concrete cylinder sealed at top and bottom, exposed to a constant concentration of sodium sulfate at its outer surface, are formulated. The resulting nonlinear governing differential equations are converted into a system of nonlinear algebraic equations using a forward finite difference scheme in space and a backward difference in time. The nonlinear algebraic equations are solved simultaneously using constrained minimization technique till the water reaches the center of the cylinder. The results obtained for ingress without chemical reactions agree with those predicted by Fick’s equation. The axial expansion of the cylinder and the increase in the value of Young’s modulus of the part of concrete which reacted with sulfates agree qualitatively with the experiments. - 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. - PublicationOn measurement of dynamic modulus for bituminous mixtures(02-09-2019)
;Deepa, S.; Murali Krishnan, J.The AASHTO:TP-79 (2010), Standard method of test for determining the dynamic modulus and flow number for hot mix asphalt using the asphalt mixture performance tester (AMPT) stipulates the test procedure for the measurement of dynamic modulus of bituminous mixtures. In this test, the stress–strain–time data for different frequencies (from 25 to 0.01 Hz) are generated and used in the calculation of dynamic modulus. In this investigation, dynamic modulus data of four types of bituminous concrete mixtures (an unmodified binder and three modified binders) are studied using this protocol. The experiments showed that the total strain decreased with time at higher temperatures and at lower frequencies while at lower temperatures and higher frequencies, the total strain was seen increasing. It was also observed that at higher temperatures and low frequencies, the phase lag decreased with a decrease in frequency. While many studies have reported such results, these are normally called as ‘anomalous’ and ascribed to the errors in measurement mechanisms. These observations seem to have not been investigated within the context of the viscoelastic behaviour of the material. This study shows that the so called ‘anomaly’ is a response shown by a viscoelastic material. In the current study, the analysis of the data showed that the increasing and decreasing trend in strain can be attributed to two phenomena: the creep due to successive loading and the recovery of the residual deformation in the material due to a reduction in load level. It is demonstrated that the observed material response for the test conducted as per this test procedure can be qualitatively predicted using many viscoelastic models, however, one has to take into account the entire load history. - PublicationA three dimensional constitutive model for plain cement concrete(10-04-2019)
;Gokulnath, C. ;Varaprasad, DaraThe validity of some of the assumptions made during systematic development of constitutive relation – homogeneity, isotropy, and non-dissipative response – is examined experimentally by testing plain concrete cylinders in the circumferential displacement controlled uniaxial compression tests. The tested cylinders indicate that the surface strains are not uniform and that the principal direction of the strain varies with the magnitude of the applied load. Hence, these cylinders are either deforming from a stressed state or anisotropic or both. The percentage dissipation computed as the area between the loading and unloading curves normalized using the area under the unloading curve is less than 10 percent up to 90 percent of the peak load. Therefore the mechanical response of concrete can be considered as non-dissipative. Assuming that the magnitude of the residual stresses present in the concrete panels would be small compared to the stresses arising due to the applied load, these residual stresses are ignored. Consequently, using the implicit constitutive theory framework for isotropic and compressible materials undergoing a non-dissipative process from a stress-free reference configuration, a three-dimensional constitutive relation for plain concrete is proposed. The material parameters in the proposed model are estimated from the uniaxial compression test and equal biaxial compression test. These parameters are expressed using initial Young's modulus, initial Poisson's ratio, maximum uniaxial compressive stress, the axial and transverse strain corresponding to the maximum uniaxial compressive stress, maximum equal biaxial compressive stress and the equal biaxial strain corresponding to maximum equal biaxial compressive stress. The ability of the proposed model to capture the response of various grade and type of concrete in ten biaxial experiments reported in the literature is examined. It is found that despite the limiting assumptions, the compression-compression, compression-tension and tension-tension stress strain response of the concrete in these ten experiments are adequately captured by the proposed model with mean R 2 value of 0.94. - PublicationOn large elastic deformation of prestressed right circular annular cylinders(01-01-2011)We formulate and study inflation, extension and twisting of prestressed cylindrical shells that are isotropic in the stress free configuration. We establish that if the prestresses vary only radially in the annular cylinder then a deformation field of the form r=r(R), θ=ΘΩZ, z=λZ is possible in annular cylinders made of any incompressible material and find sufficient conditions for the deformation to be possible when made of compressible materials. When the material is capable of undergoing large elastic deformations and has a non-linear constitutive relation, for the cases studied here, there is up to 26 percent variation in the boundary loads required to engender a given boundary displacement between the prestressed and stress free annular cylinders. On the other hand, the difference in the realized deformation field is only marginal (less than 2 percent). These are unlike the case wherein the material obeys Hooke's law and undergoes small deformations. This study has some relevance to the deformation of blood vessels. © 2010 Elsevier Ltd. All rights reserved.
- «
- 1 (current)
- 2
- 3
- »