Constant Shear Rate Tests Research Articles

RHEOLOGICAL CHARACTERIZATION OF ASEPTICALLY PACKAGED PUDDING

ABSTRACT The flow behavior of commercially available, aseptically packaged vanilla pudding was measured using a Thermo Haake RheoStress rheometer (RS1, Thermo Electron Corporation, Waltham, MA) with a concentric cylinder system. Six different shear rates, ranging from 1 to 100/s, and three reasonable serving temperatures were investigated using constant shear rate tests. A time‐dependent, Herschel–Bulkley model characterized the thixotropic nature of pudding. The model's five parameters were related to temperature. The model was validated at three constant shear rates and at two different temperatures, and was found to predict viscosity well as a function of time, shear rate and temperature.

Magnetorheological Fluid Behavior Under Constant Shear Rates and High Magnetic Fields Over Long Time Periods

This paper presents a new magnetorheological (MR) cell design along with a study of the magnetic field, shear rate, and time/shear strain influences on the properties and behavior of a MR fluid tested for long periods of time. The MR cell was designed to adapt a commercially available rheometer to measure the rheological properties of the fluid. Overall characteristics of the designed MR cell output capability are provided. Constant shear rate tests, two hours in duration, have been performed at shear rates between 0.1l∕s and 200l∕s under magnetic field intensities up to 0.4T. The rheological measurements indicated that over time the fluid’s shear stress magnitude decreases until it reaches a steady state. The time required to reach the steady state depends on both the magnetic field strength and the shear rate. The higher the field and the smaller the shear rate the shorter the time for the steady state to be reached.

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

AbstractThe degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005

Plastic Deformation Kinetics of 95.5Sn4Cu0.5Ag Solder Joints

The plastic deformation kinetics of 95.5Sn4Cu0.5Ag solder joints were determined in monotonic loading shear over the temperature range of 25°–150°C using three types of tests: (a) constant shear rate, (b) constant shear stress (creep), and (c) differential tests (changes in shear rate or temperature during an otherwise isothermal constant shear rate test). The deformation kinetics were evaluated in terms of the Dorn high temperature plastic deformation equation γ˙p=A(μb/kT)D(b/d)P(τ/μ)n where γ˙p is the shear rate, μ the shear modulus, b the Burgers vector, D the appropriate diffusion coefficient, d the grain size and τ the shear stress. A, p, and n are constants whose values depend on the rate controlling mechanism. It was found that n increased with stress from ~4 at 2 MPa to ~20 at 25 MPa, relatively independent of temperature. The activation ΔH was determined to be 21.1 ± 2 kcal/mole. The constant A, however, decreased with temperature from a value of ~1018 at 25°C to ~1010 at 150°C. The values of n and ΔH suggest that dislocation glide and climb is the rate controlling mechanism and hence that p ≈ 0. It is speculated that the large decrease in A with temperature may be the result of an effect on the microstructure.

Hardening and softening properties of soybean protein-water suspending systems.

The apparent viscosities of glycinin (11S), β-conglycinin (7S) and acid-precipitated protein (APP) of soybean suspending systems and their heated gels were investigated using a modified coaxial cylinder viscometer. A hybrid program was established: (i) cyclic temperature test (20→90→20°C) under constant shear rate and (ii) cyclic shearing test (48.7→243.7→ 48.7 sec−1) under isothermal conditions. The viscosities of the soy protein suspending system (12 %, w/v) gradually decreased with increasing temperature to about 70°C. Thereafter, characteristic behavior depended upon the sort of soy protein. The apparent viscosity of 7S globulin increased considerably, especially at lower ionic strength (μ =0.01). However, the viscosity of 11S globulin remained almost unchanged under the different temperatures and ionic conditions used. A considerable increase in viscosity was found in the cooling process rather than in the heating process with 7S globulin and APP. A noticeable thioxotropic characteristic was found in...

Thixotropy and Rheopexy of TiO<SUB>2</SUB>-Water Suspensions

Constant shear-rate tests and cyclic shearing tests were carried out in a coaxial cylinder viscometer for TiO2-water suspensions stabilized with various amounts of sodium pyrophosphate under a wide variety of histories of shear-rate and rest period before measurements. The electrophoretic mobilities and sedimentation behavior were also measured as a means of studying the stability of the suspension and the state of aggregate. The rheological properties of these suspensions were greatly influenced by the previous history of shear-rate and rest period, and both of thixotropic and rheopectic behavior were observed depending on the history. From these results, the structural rebuild-up due to the mechanical force by shear was recognized to be different in nature from that due to the Brownian motion during rest. These were attributed to aggregation of particles at the primary minimum in the potential energy curve, and to aggregation at the secondary minimum, respectively. The mechanism of the rheopexy observed in this study was attributed to the transient behavior resulting from the structural change under shear from the aggregates at the secondary minimum to those at the primary minimum in the potential energy curve. Thixotropic behavior, as well as non-Newtonian behavior in an equilibrium flow curve, was also studied on the basis of the theory of stability of lyophobic colloids.