Polymer Flow Behavior from Multispeed Viscometry

1965 ◽  
Vol 38 (4) ◽  
pp. 769-781 ◽  
Author(s):  
W. E. Wolstenholme
Keyword(s):  
Activation Energy ◽  
Flow Curve ◽  
Flow Behavior ◽  
Standard Procedure ◽  
Isothermal Flow ◽  
Thermal Dependence ◽  
Flow Curves ◽  
Polymer Flow ◽  
Constant Rate ◽  
Constant Viscosity

Abstract A practical viscometric technique has been developed for measuring flow of commercial elastomeric and thermoplastic materials at processing temperatures. A standard procedure for testing bulk polymer samples in a modified shearing disk Mooney viscometer with rotor speeds from .05 to 77 rpm is described in detail. Research, development or process control personnel can rapidly convert viscometer torque dial readings at the various rotor speeds to an isothermal flow curve in absolute units of shear stress and rate of shear by either of two methods shown by examples. Total time to test a polymer sample and plot the flow curve is less than one hour. Representative flow curves illustrate how polymers with essentially equivalent ML-4 @ 212° F can have large differences in flow at processing conditions. A set of isothermal flow curves covering a desired temperature range provides an excellent estimate of processing behavior over a range of temperatures. Numerical determination of the thermal dependence of flow is easily evaluated in terms of activation energy at constant shearing stress, constant rate of shear, or constant viscosity. Activation energy is a useful constant for characterization of non-Newtonian polymer flow.

scholarly journals FepiM: A Novel Inverse Piecewise Method to Determine Isothermal Flow Curves for Hot Working

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 602
Author(s):  
Aditya Vuppala ◽  
Alexander Krämer ◽  
Johannes Lohmar ◽  
Gerhard Hirt
Keyword(s):  
Flow Curve ◽  
Elevated Temperatures ◽  
Isothermal Flow ◽  
Inverse Methods ◽  
Material Behavior ◽  
Maximum Deviation ◽  
Compression Tests ◽  
Complex Flow ◽  
Flow Curves ◽  
Curve Determination

In forming simulations, flow curves are cardinal inputs to predict features, such as forming forces and material flow. The laboratory-scale experiments to determine them, like compression or tensile tests, are affected by deformation heating, restricting direct flow curve determination. In principle, the current analytical and inverse methods determine flow curves from these tests, but while the analytical methods assume a simplified temperature profile, the inverse methods require a closed-form flow curve equation, which mostly cannot capture complex material behavior like multiple recrystallization cycles. Therefore, the inverse piecewise flow curve determination method “FepiM” previously developed and published by the current authors is extended by introducing a two-step procedure to obtain isothermal flow curves at elevated temperatures and different strain rates. Thereby, the flow curve is represented as tabular data instead of an equation to reproduce complex flow curve shapes while also compensating the effect of inhomogeneous temperature profiles on the flow stress. First, a flow curve at the highest temperature is determined. In the second step, using this first flow curve as a reference, the flow curves at lower temperatures are obtained via interpolation. Flow curves from conventional compression tests for aluminum and copper in the temperature range of 20–500 °C are predicted, and it is shown that these flow curves can reproduce the experimental forces with a maximum deviation of less than 1%. Therefore, the proposed new piecewise method accurately predicts isothermal flow curves for compression tests, and the method could be further extended to highly inhomogeneous methods in the future.

Vane Rheometry with a Large, Finite Gap

2002 ◽  
Vol 12 (2) ◽  
pp. 81-87 ◽  
Author(s):  
Christophe Baravian ◽  
Audrey Lalante ◽  
Alan Parker
Keyword(s):  
Viscoelastic Properties ◽  
Complex Fluids ◽  
Standard Procedure ◽  
Effective Radius ◽  
Stress Factors ◽  
Work Flow ◽  
Flow Curves ◽  
Alternative Procedures ◽  
Newtonian Liquids ◽  
Stream Lines

Abstract The vane geometry with a large gap is used to determine the Newtonian, non-Newtonian and viscoelastic properties of complex fluids. We show that when this geometry is carefully characterized, it can be used for precise rheometry. A novel effective cylinder approximation is used to obtain the shear rate and shear stress factors. The effective radius is found to be close to the height of the triangle formed by joining the tips of adjacent blades. This result differs significantly from that of previous work. Flow visualization has been used to confirm that the stream lines bend towards the centre between the blades. These factors can be used to determine the flow curves of non-Newtonian liquids, using Krieger’s power law expansion. The standard procedure for using the vane to determine the yield stress is also carefully investigated and alternative procedures are suggested.

scholarly journals Thermal dependence of the antioxidant enzymes superoxide dismutase, catalase, and peroxidase in foliage of Iris pumila L.

2009 ◽  
Vol 61 (3) ◽  
pp. 441-446 ◽  
Author(s):  
Ana Vuleta ◽  
Branka Tucic
Keyword(s):  
Activation Energy ◽  
Superoxide Dismutase ◽  
Antioxidant Enzymes ◽  
Temperature Increase ◽  
Specific Activity ◽  
Thermal Dependence ◽  
Full Sunlight ◽  
Iris Pumila ◽  
Temperature Optima

Thermal dependence of the enzymes SOD, CAT, and POD was investigated in leaves of Iris pumila plants inhabiting two contrasting light environments, a sun-exposed dune site and a woodland understory. At the same assay temperature, both the specific activity and the activation energy of SOD and CAT were higher in plants inhabiting vegetation shade than in those experiencing full sunlight. Conversely, the temperature optima for the two enzymes did not differ between alternative radiation environments. The specific activity of POD increased with temperature increase, and was always greater in plants growing under full sunlight than in those from vegetation shade. The activation energy of POD was higher than that of SOD or CAT, being lower in sun-than in shade-exposed plants.

scholarly journals Mathematical models to describe the drying process of Moringa oleifera leaves in a convective-air dryer

2021 ◽  
Author(s):  
Kivaandra Dayaa Rao Ramarao ◽  
Zuliana Razali ◽  
Chandran Somasundram
Keyword(s):  
Activation Energy ◽  
Mathematical Models ◽  
Moringa Oleifera ◽  
Effective Diffusivity ◽  
Drying Process ◽  
Constant Rate ◽  
Rate Period ◽  
Moringa Oleifera Leaves ◽  
Air Dryer ◽  
Kinetics Of

Drying kinetics of Malaysian Moringa oleifera leaves was investigated using a convective-air dryer. The drying parameters were: temperature (40, 50, 60, 70 °C), air velocity (1.3 m s<sup>–1</sup>, 1.7 m s<sup>–1</sup>). The drying process took place in the falling rate period and there was an absence of a constant rate period in this experiment. Six mathematical models (Lewis, Henderson and Pabis, Wang and Singh, Peleg, Page, and logarithmic) were selected for the description of drying characteristics of the leaves. The Wang and Singh model was determined as the best model based on the highest overall coefficient determinant (R<sup>2</sup>) and the lowest overall root mean square error (RMSE). The effective diffusivity (D<sub>eff</sub><sub> </sub>) was also calculated which was in the range of 3.98 × 10<sup>–11</sup> m<sup>2</sup> s<sup>–1</sup> to 1.74 × 10<sup>–10</sup> m<sup>2</sup> s<sup>–1. </sup>An Arrhenius relation was constructed to determine the activation energy for the samples in the convective air dryer. The activation energy for M. oleifera leaves was 39.82 kJ mol<sup>–1</sup> and 33.13 kJ mol<sup>–1</sup> at drying velocities of 1.3 m s<sup>–1</sup> and 1.7 m s<sup>–1</sup>, respectively.

Constitutive Modeling of Low-Temperature Superplastic Flow of Ultrafine Ti-6Al-4V Sheet Material

2010 ◽  
Vol 433 ◽  
pp. 235-240 ◽  
Author(s):  
S. Lee Semiatin ◽  
Gordon A. Sargent
Keyword(s):  
Low Temperature ◽  
Flow Behavior ◽  
Sheet Material ◽  
Superplastic Flow ◽  
Flow Softening ◽  
Flow Localization ◽  
Flow Curves ◽  
Localization Model ◽  
Simple Flow ◽  
Stress Flow

The low-temperature superplastic flow behavior of two lots of Ti-6Al-4V sheet with an ultrafine microstructure was modeled. One lot (Sheet A) had an equiaxed-alpha starting microstructure; the flow stress/flow hardening exhibited by this material was explained on the basis of the Bird-Mukherjee-Dorn constitutive equation. The other material (Sheet B), having a mixed equiaxed- and remnant-lamellar alpha microstructure, underwent flow softening, flow hardening, or steady-state flow depending on test temperature and strain rate. These behaviors were interpreted in the context of a dynamic spheroidization model. The apparent flow softening at the end of all of the flow curves was explained using a simple flow-localization model.

Some Observations on the Relationship Between Lubricant Mechanical and Dielectric Transitions Under Pressure

1980 ◽  
Vol 102 (2) ◽  
pp. 229-234 ◽  
Author(s):  
S. Bair ◽  
W. O. Winer
Keyword(s):  
Atmospheric Pressure ◽  
Frequency Range ◽  
Two Fluids ◽  
Constant Rate ◽  
Constant Viscosity ◽  
The Relationship ◽  
Dielectric Transition

Viscoelastic transition measurements of several lubricants by volume dilatometry to pressures of 1.75 GPa, dielectric transitions at atmospheric pressure on five fluids in a frequency range of 0.2 to 500 kHz and on two fluids in the same frequency range to pressures of 0.55 GPa are reported. Lines of constant rate dilatometry transition, constant rate dielectric transition and constant viscosity are shown to be essentially parallel on a temperature-pressure diagram.

scholarly journals On the Zener–Hollomon Parameter, Multi-Layer Perceptron and Multivariate Polynomials in the Struggle for the Peak and Steady-State Description

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1413 ◽  
Author(s):  
Petr Opěla ◽  
Petr Kawulok ◽  
Ivo Schindler ◽  
Rostislav Kawulok ◽  
Stanislav Rusz ◽  
...  
Keyword(s):  
Steady State ◽  
Flow Stress ◽  
Flow Curve ◽  
Multivariate Polynomials ◽  
Multi Layer Perceptron ◽  
Stress Evolution ◽  
Flow Curves ◽  
Hollomon Parameter ◽  
Wide Range ◽  
Stress Models

Description of flow stress evolution, specifically an approximation of a set of flow curves acquired under a wide range of thermomechanical conditions, of various materials is often solved via so-called flow stress models. Some of these models are associated with a description of significant flow-curve coordinates. It is clear, the more accurate the coordinates description, the more accurate the assembled model. In the presented research, Zener–Hollomon-based relations, multi-layer perceptron networks and multivariate polynomials are employed to describe the peak and steady-state coordinates of an Invar 36 flow curve dataset. Comparison of the utilized methods in the case of the studied alloy has showed that the suitable description is given by the multivariate polynomials although the Zener–Hollomon and perceptron networks also offer valuable results.

Modelling of Flow Behaviour of Magnesium Alloys

2016 ◽  
Vol 716 ◽  
pp. 360-367
Author(s):  
Carlo Bruni
Keyword(s):  
Numerical Simulation ◽  
High Temperature ◽  
Low Temperature ◽  
Magnesium Alloys ◽  
Flow Curve ◽  
Flow Behaviour ◽  
Temperature Deformation ◽  
Flow Curves ◽  
High Deformation ◽  
Modelling Approach

The present investigation aims at studying the flow behaviour of magnesium alloys under different conditions in terms of temperature, deformation velocities and deformation. The modelling approach was based on a proposed equation to model the shape of each flow curve through different variables. The modelled flow curves were subsequently compared with those obtained with experiments. The models were validated on flow curves not used in the building stage. It was observed that, for low temperature values, high deformation velocities and deformations the final part of the flow curve has to be adapted in order to be adopted for the description of material in the numerical simulation. In other words it needs to be extrapolated. Also for the high temperature, the flow softening has to be limited in order to allow the extrapolation queue required for elevated deformations. The deformation value at which the extrapolation can start can be predicted with an other proposed equation detailed in the paper.

Prediction of Field Aging Gradient in Asphalt Pavements

2015 ◽  
Vol 2507 (1) ◽  
pp. 19-28 ◽  
Author(s):  
Xue Luo ◽  
Fan Gu ◽  
Robert L. Lytton
Keyword(s):  
Activation Energy ◽  
Prediction Model ◽  
Prediction Models ◽  
Fast Rate ◽  
Chemical Properties ◽  
Asphalt Pavements ◽  
Model Parameters ◽  
Void Content ◽  
Constant Rate ◽  
Rate Period

The aging of asphalt pavements is a key factor that influences pavement performance. Aging can be characterized by laboratory tests and prediction models. Common aging prediction models use the change of physical or chemical properties of asphalt binders based on regression techniques or aging reaction kinetics. The objective of this study was to develop a kinetics-based aging prediction model for the mixture modulus gradient in asphalt pavements to study long-term in-service aging. The proposed model was composed of three submodels for baseline modulus, surface modulus, and aging exponent to define the change of the mixture modulus with pavement depth. The model used kinetic parameters (aging activation energy and preexponential factor) of asphalt mixtures and combined the two reaction rate periods (fast-rate and constant-rate). Laboratory-measured modulus gradients of 29 field cores at different ages were used to determine the model parameters. The laboratory testing condition was converted to the field condition at a given age and corresponding temperature by introducing the rheological activation energy to quantify the temperature dependence of field cores at each age. The end of the fast-rate period or the beginning of the constant-rate period was accurately identified to model these two periods and to determine the associated parameters separately. The results showed that the predictions matched well with the measurements and the calculated model parameters were verified. The proposed aging prediction model took into account the major factors that affect field aging speed of an asphalt pavement, such as the binder type, aggregate type, air void content, pavement depth, aging temperature, and aging time.

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