 | viscoelasticity |
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 | Unsteady Hele Shaw Flow of a Conducting Rivlin Ericksen Fluid
Author : Sreenivasan, K.;Bathaiah, D.
Source : Defence Science Journal ; Vol:43(4) ; 1993 ; pp 419-428
Subject : 532.542 Fluid Dynamics
Keywords : Magnetic field;Viscoelasticity
Abstract : This paper aims to study the unsteady Hele-Shaw flow of conducting Rivlin-Ericksen fluid under the influence of a uniform transverse magnetic field. The study has been carried out when the pressure gradient is (i) proportional to e/sup int/, (ii) zero for t < 0 and equal to a constant for t >= 0, and (iii) proportional to e/sup -nt/. It is interesting to note that the time for the motion to become steady when started from rest(case ii) is of the order ~ 4 s/sup 2/ / where s is the viscoelastic parameter. The rheological equation of the Rivlin-Ericksen fluid is described in section 2. The expressions for velocity components u and v of the fluid in x and y directions are derived in section 3. The effects of magnetic field and viscoelasticity are discussed in section 4. |
| | Viscoelastic Modelling of Solid Rocket Propellants using Maxwell Fluid Model
Author : Shekhar, Himanshu;Sahasrabudhe, A.D.
Source : Defence Science Journal ; Vol:60(4) ; 2010 ; pp 423-427
Subject : 532.5 Hydrodynamics;629.76 Rockets and Missiles ;Defence Science Journal
Keywords : Solid rocket propellants;mechanical properties;viscoelasticity;Maxwell fluid;spring constant;damping coefficient
Abstract : Maxwell fluid model consisting of a spring and a dashpot in series is applied for viscoelastic characterisation of solid rocket propellants. Suitable values of spring constant and damping coefficient were employed by least square variation of errors for generation of complete stress-strain curve in uniaxial tensile mode for case-bonded solid propellant formulations. Propellants from the same lot were tested at different strain rates. It was observed that change in spring constant, representing elastic part was very small with strain rate but damping constant varies significantly with variation in strain rate. For a typical propellant formulation, when strain rate was raised from 0.00037/s to 0.185/s, spring constant K changed from 5.5 MPa to 7.9 MPa, but damping coefficient D was reduced from 1400 MPa-s to 4 MPa-s. For all strain rates, stressstrain curve was generated using Maxwell model and close matching with actual test curve was observed. This indicates validity of Maxwell fluid model for uniaxial tensile testing curves of case-bonded solid propellant formulations. It was established that at higher strain rate, damping coefficient becomes negligible as compared to spring constant. It was also observed that variation of spring constant is logarithmic with strain rate and that of damping coefficient follows power law. The correlation coefficients were introduced to ascertain spring constants and damping coefficients at any strain rate from that at a reference strain rate. Correlation for spring constant needs a coefficient H, which is function of propellant formulation alone and not of test conditions and the equation developeds K2 = K1 + H ´ ln{(de2/dt)/(de1/dt)}. Similarly for damping coefficient D also another constant S is introduced and prediction formula is given by D2 = D1 ´ {(de2/dt)/(de1/dt)}S. Evaluating constants H and S at different strain rates validate this mathematical formulation for different propellant formulations. Stress-strain curves for solid propellants can be generated at those strain rates at which actual testing is not possible. Close matching of test and predicted stress-strain curve indicates propellant behavior as visco-elastic Maxwell fluid. |
| | Aging Maxwell Constitutive Model for Concrete
Author : Suter, Milan;Benipal, Gurmail S.
Source : Defence Science Journal ; Vol:58(2) ; 2008 ; pp 220-226
Subject :
Keywords : Constitutive model;Aging creep;Viscoelasticity;Mature concrete;Microprestress;Linear elastic concrete
Abstract : Fully-hydrated concrete not involved in any reaction has been observed to exhibit aging creep. Both the solidification theory and the dissolution-precipitation theory are incapable of predicting such a behaviour. The microprestress theory proposed for this purpose is based upon an ambiguous physical mechanism. In this paper, a constitutive model motivated by Drozdov's adaptive link mechanism has been proposed. The model is capable of predicting aging creep, recovery and relaxation for linear elastic concrete subjected to diverse load histories and temperatures. The theoretical significance of the proposed aging Maxwell model has been critically evaluated |
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