Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.

Rheological characterization of the time and strain dependence for polyisobutylene solutions

Abstract: The rheological response of polyisobutylene (PIB) solutions in Decalin and a related standard fluid S1 has been characterized in dynamic oscillatory flow, step strain, step-shear rate and steady shear using a Rheometrics RDSII rheometer. The time dependence represented as a discrete spectrum of relaxation times and the strain dependence characterized as an exponential damping function have been presented as a function of PIB concentration. The relaxation spectrum was calculated from the dynamic storage modulus and loss modulus. The damping function was determined from the non-linear relaxation modulus in a step-strain experiment. The Wagner integral viscoelastic model incorporated with the relaxation and the damping function has been used to predict the stress growth and the steady-shear behaviour, which were compared with the experimental data. A novel extensional rheotester was also used in this study to measure the stretching response of polymer solutions. The data gave a near single relaxation time for each solution, and this single relaxation time obtained from uniaxial extension was correlated to the relaxation spectrum obtained in simple shear.

Integration approach of the Couette inverse problem of powder type self-compacting concrete in a wide-gap concentric cylinder rheometer

Abstract: For powder type self-compacting concrete (SCC) mixes, commonly used in Belgium, a shear thickening (Herschel–Bulkley) flow behaviour of the fresh mixes is quite often observed. A longstanding problem in rheometry is the so-called “Couette inverse problem”, where one tries to derive the flow curve τ ( γ ˙ ) from the torque measurements T(N) in a (wide-gap) concentric cylinder (Couette) rheometer, with T the torque registered at the inner, stationary cylinder and N the rotational velocity of the outer, rotating, cylinder. In this paper, the Couette inverse problem is approached by means of the integration method in order to convert T(N) into τ ( γ ˙ ) for a wide-gap (Ro/Ri = 1.45) concentric cylinder rheometer. The approach consists in the decoupling of the flow resistance and the power-law flow behaviour after exceeding the flow resistance. The integration approach is validated by experimental verification with different powder type SCC mixtures. By means of illustration, the results of one limestone powder type SCC mixture with different superplasticizer contents are shown in this paper.

Rotary Clamp in Uniaxial and Biaxial Extensional Rheometry of Polymer Melts

Abstract: The rotary clamp consisting of a pair of gears is a basic construction element for the design of various types of extensional rheometers for polymer melts. With the most recent model of the uniaxial extensional rheometer, built with rotary clamps, homogeneous deformations of Hencky strains up to e=7 have been performed with a low‐density polyethylene melt. For the evaluation and discussion of results from tests with large deformations, it is vital that parameters which characterize the quality of each test be defined and measured. Otherwise, the measured force and the rotational speed of the clamps might be of little relevance for the stress, strain, and strain rate within the sample. The biaxial extensional rheometer consists of eight rotary clamps in a circular arrangement. With this new instrument, extensional Hencky strains up to e11=e22=2.2 can be achieved for a polyisobutylene sample. Such a high deformation corresponds to a compression in the third direction of e33=−4.4. The material within the sam...

Melt Rheology and its Applications in the Plastics Industry

Abstract: Preface.- 1.Introduction to Rheology: 1.1 What is rheology?.- 1.2 Why rheological properties are important.- 1.3 Stress- a measure of force.- 1.4 Strain - a measure of deformation.- 1.5 Rheological Phenomena.- 1.6 Why polymeric liquids are non-Newtonian and elastic.- 2.Viscosity and the Normal Stress Differences: 2.1 Simple shear and steady simple shear.- 2.2 Viscometric flow.- 2.3 The viscometric functions.- 2.4 The Viscosity.- 2.5 Normal stress differences.- References.- 3. Linear Viscoelasticity: 3.1 Introduction.- 3.2 Stress relaxation and the relaxation modulus.- 3.3 The Boltzmann superposition principle.- 3.4 Start-up of steady simple shear.- 3.5 Relaxation moduli of rubbers and molten polymers.- 3.6 The Maxwell model for the relaxation modulus.- 3.7 The generalized Maxwell model and the discrete relaxation spectrum.- 3.8 The continuous spectrum.- .9 Creep and creep recovery: The compliance.- 3.10 Start-up of steady simple extension.- 3.11 Small amplitude oscillatory shear.- 3.12 Inferring a discrete relaxation spectrum from storage and loss moduli.- 3.13 Combining creep and oscillatory shear data.- 3.14 Time-temperature superposition.- 3.15 Cole-Cole and related plots of linear data.- 3.16 Van Gurp-Palmen Plot of Loss Angle Versus Complex Modulus.- 3.17 Storage and loss moduli of molten linear polymers.- 3.18 The plateau modulus and the molecular weight between entanglements.- 3.19 The Rouse-Bueche model for unentangled melts.- 3.20 Tube models for entangled melts.- 3.21 Molecular weights fo the onset of entanglement effects.- 3.22 Summary.- References.- 4. Nonlinear Viscoelasticity - Phenomena: 4.1 Introduction.- 4.2 Nonlinear phenomena from a tube modelp of view.- 4.3 Nonlinear stress relaxation.- 4.4 Dimensionless groups used to plot rheological data.- 4.5 The viscosity in terms of the tube model.- 4.6 Transient shear tests at finite rates.- 4.7 Extensional flow behavior - Introduction.- 4.8 Extensional Flow Behavior of Melts.- 4.9 Shear modification.- 4.10 Time-temperature superposition of nonlinear properties.- References.- 5. Nonlinear Viscoelasticity - Models: 5.1 Introduction.- 5.2 Tensor notation.- 5.3 The stress tensor.- 5.4 A strain tensor for infinitesimal deformations.- 5.5 The Boltzmann superposition principle in tensor form.- 5.6 Strain tensors for large, rapid deformations.- 5.7 Integral constitutive equations based on continuum mechanics.- 5.8 Continuum differential constitutive equations.- 5.9 Constitutive equations from molecular models.- 5.10 Numerical simulation of melt flows.- References.- 6. Measurement Techniques: 6.1. Introduction.- 6.2. Rotational and other drag-flow rheometers.- 6.3. Pressure-driven rheometers.- 6.4 On-line rheometers.- 6.5 High-throughput rheometry.- 6.6. Extensional rheometers.- 6.7 Torque Rheometers.- 6.8 Using Rheology for statistical process control.- 6.9 Sample Stability: Thermo-oxidative degradation and hydrolysis.- Reference.- 7. Rheology and molecular structure: 7.1 Rheology and structure of linear polymers.- 7.2 Long-chain branching and melt rheology.- References.- 8. Role of Rheology in Plastics Processing: 8.1.Introduction.- 8.2 Flow in simple channels and dies.- 8.3 Flow in an extruder.- 8.4 Sheet extrusion/film casting.- 8.5 Extrusion coating.- 8.6. Film blowing.- 8.7 Blow molding.- 8.8 Injection molding.- 8.9. Rotational molding.- 8.10. Foam Extrusion.- References.- Appendix A Structural and Rheological Parameters for Several Polymers.- Appendix B The Displacement Gradient Tensor.- Subject Index.

Shear rheometry of fluids with a yield stress

Abstract: This work is concerned with the measurement of viscometric material functions of greases, which are fluids with a yield stress. Rheometers working under controlled stress or under kinematically controlled conditions have been used in plane and cone geometry. Viscometric functions and the problems encountered in measurements are examined simultaneously. It is shown how fracture and slippage at boundng surfaces alter the measurements of the bulk properties and how they can be controlled. Fractures limit the amplitude of deformation; hence the rate of the deformation and duration of measurements. Slippage is a limiting factor at low rates of deformation, but it can be suppressed. Within the range defined by these two limiting factors, viscometric properties have been measured: elastic properties, yield values, and start up, steady and unsteady viscometric material functions similar to those for melted polymers have been found.