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Parag Ravindran
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Parag Ravindran
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Parag Ravindran
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Parag, R.
Ravindran, Parag
Ravindran, P.
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28 results
Now showing 1 - 10 of 28
- PublicationA continuum model for predicting strain evolution in carbon fiber-reinforced composites subjected to cyclic loading(01-03-2022)
;Sadagoapan, T. S.; Murthy, H. S.N.The focus of this work is on layered carbon fiber-reinforced polymers (CFRPs) subjected to cyclic loading. The response of CFRPs to cyclic loading is dictated by a variety of mechanisms that come into operation due to repetitive loading. These are quite distinct from mechanisms at play for conventional metals and alloys. Microscopic changes manifest as degradation in properties over thousands of cycles. Due to complex interactions and inherent randomness, capturing the multitude of microscopic effects and collating their effects to manifest as macroscopic changes is a difficult task. Here, the focus is on developing a continuum model which accounts for microscopic changes in an indirect, averaged manner. It is of value as it enables good estimates of material behavior without the need for detailed microscopic information. The intent is to capture the stiffness degradation over the first 10,000 cycles before there are visible changes in the material. For the material under study here, the degradation manifests in the transverse direction earlier than the longitudinal (loading) direction. The model successfully captures this behavior. The model is calibrated against experimental data from the literature. - PublicationInfluence of Viscosities of PDA Pitch and Flux on Blended Bitumen Viscosity(01-01-2017)
;Chakkoth, Uma; Murali Krishnan, J.The production of bitumen in Indian refineries is carried out by air blowing and component blending. In the component blending process, a highly viscous propane deasphalted (PDA) pitch is blended with a less viscous flux. The choice of the proportion of these two components is normally arrived at to meet the required technical specification such as penetration at 25°C and viscosity at 60 and 135°C. However, it is not clear at this point in time, the influence of constituent materials on the rheological response of the binder. In this investigation, two ratios of PDA pitch and Flux (75:25, 80:20) were blended in the laboratory. The rheological characterization of constituents and the final blend were carried out using a rotational viscometer at temperatures of 120, 140 and 160°C. Four viscosity mixing 'rules' were used to estimate the final blend viscosity from the individual constituent viscosities. The predictions varied with a wide range of errors. - PublicationInvestigation on the influence of air voids and active filler on the mechanical response of bitumen stabilized material(01-03-2018)
;Nivedya, M. K.; ; Krishnan, J. MuraliCold in-place recycling technology for reclaimed material in pavement rehabilitation holds promise as a solution to resource scarcity. This paper reports results of a systematic experimental investigation of the material produced by this technique and in particular the role of cement and air void content. The internal structure is characterized using computed tomography and environmental scanning electron microscopy. A tension and tension-compression test is carried out to characterize the response of the material at 15 and 45°C. From microscopy, it is seen that the addition of cement did not result in formation of hydration compounds, but instead aids in densifying the material substantially. From the mechanical experiments, it is seen that the response of the material is clearly viscoelastic at the temperatures at which it is tested. The experimental data are used to find relevant linear viscoelastic parameters, and a methodology to compute these parameters directly is presented. - PublicationModelling sand-asphalt mixtures within a thermodynamic framework: Theory and application to torsion experiments(01-04-2009)
; ;Krishnan, J. M. ;Masad, E.Rajagopal, K. R.Sand-asphalt mixtures are difficult to model, partly due to their composition and partly due to the complex interplay among their constituents. This work is concerned with the development of an anisotropic model to describe the nonlinear behaviour of sand-asphalt mixtures. A general thermodynamic framework is used, which allows for the material to have multiple natural configurations corresponding to its underlying structure. The evolution of the natural configuration takes place in a thermodynamically consistent manner. The model developed is corroborated using experimental results published by Ravindran et al. (2007a,b) on torsion tests of sand-asphalt specimens over a range of conditions. © 2009 Taylor & Francis. - PublicationThe effect of nanoclay reinforcement on the rolling contact fatigue behaviour of polyamide(01-01-2013)
;Charles, D. Finney; Polymer nanocomposite has received great research interest in design of engineering components owing to its remarkable improvement in tribological characteristics. Rolling contact fatigue is a predominant failure mode of the many functional components like gears, bearings, cams, ball screw rods and rail wheels. Nanosize clay fillers were dispersed into the polymer using melt intercalation method to produce polymer nanocomposite material. Injection-molded disctype specimens were made to run against each other on twin-disc test rig designed in-house. To understand the behaviour of the materials, rolling contact fatigue behaviour against different contact loads under constant speed were studied. Rolling contact fatigue testing of polymer nanocomposite has revealed significant difference from the pristine PA6 behaviour in failure modality and temperature rise. Addition of nanoclay to polymer although improved the modulus and strength of the nanocomposite, deteriorated the rolling contact behaviour. Rolling contact fatigue performance of PA6 was better than that of the clay-reinforced polymer nanocomposite under all tested conditions. Polymer nanocomposite materials have shown poor wear resistance as the specific wear rate was calculated to be higher for PNC materials under rolling contact fatigue conditions. Difference in surface temperature rise in PA6 and polymer nanocomposite has led to the different failure mechanism and reduction in rolling contact fatigue life of polymer nanocomposite materials. © IMechE 2012. - PublicationAn experimental investigation into the influence of fillers on the development of normal stresses and stress relaxation in asphalt mixtures due to torsion(01-07-2007)
; ;Rajagopal, K. R. ;Krishnan, J. M.Little, D. N.This study documents the measurement of normal stresses and stress relaxation in sand-asphalt mixtures fabricated with different fillers and asphalts during torsion. Hydrated lime and limestone fillers and asphalts graded as PG64-22 and AC-30 (from Sinclair (Wyoming), Crown (Nevada), and Crown (Canada)) are used in the fabrication of the sand-asphalt mixtures. The specimens are tested in a torsional rheometer. The experimental results clearly show that the normal stresses that are developed are quite significant even for specimens tested at very low rotational rates. Also, asphalts from different sources show differences in peak normal stresses and in their relaxation pattern. The measurement of significant normal stresses is a reflection of the nonlinear character of the material and warrants the development of nonlinear constitutive models for describing their behavior. Copyright © Taylor & Francis Group, LLC. - PublicationMechanical response of polyacrylamide breast tissue phantoms: Formulation, characterization and modeling(01-05-2022)
;Rao, S. Narasimha ;Mythravaruni, Pullela; In the context of breast cancer detection, mechanical imaging is an emerging technique for screening breast cancer. In view of its promise, it deserves a detailed investigation. Development of material that can emulate tissue behavior is essential for research. This work is concerned with the fabrication of polymeric specimens to capture the mechanical behavior of human breast tissues. Three types of tissue phantoms are fabricated: fat, glandular and ductal carcinoma tissues. The fabricated phantoms are compared to available human breast tissue data obtained through compression tests and stress relaxation tests. Further, the fabricated tissue phantoms are subjected to stress relaxation tests to characterize their viscoelastic response. A finite strain viscoelastic constitute model is proposed to describe the mechanical response of the breast tissue phantoms. The model is calibrated using experimental data for phantom tissue specimens. Both phantom tissue specimens and model predictions show reasonable trends. The phantom tissues and model may be of utility in developing mechanical imaging setups. - PublicationThe effect of oxidation on the mechanical response of isolated elastin and aorta(01-06-2019)
;Mythravaruni, P.Oxidation of aorta by hydroxyl radicals produces structural changes in arterial proteins like elastin and collagen. This in turn results in change in the mechanical response of aorta. In this paper, a thermodynamically consistent constitutive model is developed within the framework of mixture theory, to describe the changes in aorta and isolated elastin with oxidation. The model is then studied under uniaxial extension using experimental data from literature. - PublicationA filled polymer melt as a new thixotropic model system and insights on efficacy of two thixotropic models(01-05-2023)
;Miriyala, Raviteja; TEVP (thixotropic elasto viscoplastic) fluids exhibit phenomenon such as shear thinning, yield stress, viscoelasticity and thixotropy. A filled polymer melt system consisting of LDPE (low density polyethylene) filled with fumed silica is presented here as a material system that exhibits the different features expected from a general TEVP fluid. It is evaluated through different rheological protocols such as steady shear, step shear, start up shear and flow reversal. Further it is compared against the experimental data corresponding to the standard TEVP material system, namely the fumed silica suspension from literature to understand the influence of dispersing medium on the breakdown and rebuilding time scales of the microstructure. It is observed that the proposed formulation which is simpler (consisting of only two constituents), with hardly any solvent evaporation, chemical aging and yields better viscoelastic transients compared to fumed silica suspension. In the proposed formulation, structural breakdown occurs on longer time scales. The rheological data of the proposed filled melt system is then compared to predictions from two different mathematical models. The comparison yields insights into the efficacy of the two models, providing some guidelines for improvement. - PublicationAn Experimental Investigation on the Influence of Annealed Microstructure on Wave Propagation(05-07-2015)
;Mini, R. S.; In this work grain growth associated with isochronous annealing in polycrystalline pure copper is studied using nonlinear ultrasonic method. In isochronous annealing, holding time is constant but annealing temperatures vary. It is observed that, grain growth due to isochronous annealing significantly influences the ultrasonic nonlinearity parameter, β. A decrease in nonlinearity parameter with increase in grain size is noticed. Further, micro-hardness measurements as well as metallographic results are presented to underscore the utility of the nonlinear ultrasonic method in gauging the progress of annealing. As the time and effort involved in this method is less, with suitable calibration, this method may be gainfully employed for determination of grain size on annealing.
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