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RHEA (Rheology Analysis)                           
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User Friendly Analysis

The RHEA™ Software User friendly analysis RHEA™ has been specifically developed for engineers working in rheology needing a rapid analysis procedure. Master-curves of stiffness or compliance information in either time or frequency domain are generated from dynamic or creep data. For example, in the asphalt industry, the Superpave specification and mixture design process involves the collection of dynamic data for both binder and mixture specifications. In the plastics industry, dynamic mechanical data is used for understanding the complex behavior of polymers over a wide range of frequency or stiffness. The RHEA™ software allows users to rapidly inspect the quality of data and to develop the interrelationships with ease. RHEA™ converts dynamic mechanical data (G', G" vs. w) from the frequency domain to the time domain, G(t) and J(t) and vice-versa. The shifted master curves are fitted using a modified non-linear Marquadt-Levenburg least squares optimization. This is followed by a numerical analysis calculating the discrete relaxation and retardation spectra (Baumgaertel and Winter, 1989). The software numerically optimizes the number of relaxation/retardation modes used in the analysis. A maximum of 32 relaxation modes can be calculated for the data sets.

This program has been developed as a general tool for performing rheological analysis of a wide variety of materials that behave according to linear visco-elastic theory.

Data files

The RHEA™ software has been configured to read data files generated with many test devices. For example with the Bohlin Rheometer the data files are named using *.d?w convention. These are read by the software and can be either Creep or Frequency Sweep data.

RHEA Data

The user can also edit choose to add/remove single data points or entire isotherms for analysis. The final data set is stored in a separate file for analysis enabling the user to develop multiple data sets for sensitivity analysis. The analysis process take only a few minutes enabling a much greater throughput and understanding of material behavior.

Verification with standard data sets

In the development of RHEA the software has been extensively tested with standard data sets. A few typical examples are illustrated below.

1. Polycarbonate

Polycarbonate Stress Relaxation; Mercier et al., JAPS 9, 447 (1965). The data shown is the G(t) isotherms which have been entered in the standard format.

RHEA data - Polycarbonate

The second plot illustrates the resulting master curve with the mode contributions (this is an option that the user chooses to display).

Polycarbonate Master Curve Plot

2. Polystyrene

Polystyrene - the data set shows results collected from dynamic testing. Often data is collected in this manner, used to produce a master curve and then transformed to G(t).

RHEA data - Polystrene

The second plot illustrates the resulting master curve G* and phase angle.

Polystrene Master Curve

The final plot shows the same data set transformed to J(t) using the spectrum analysis.

Polystrene converted to G(t) Master Curve

3. Asphalt Mixes

The plot below shows results developed from a the Superpave Shear Tester expressed as a frequency sweep.

RHEA SST Asphalt Mix Master Curve

This program has been developed as a general tool for performing rheological analysis of a wide variety of materials that behave according to linear visco-elastic theory.

Test methods considered

  • Asphalt mix and binder dynamic modulus tests (E*, G* etc.)
  • Bending Beam Rheometer (S(t) vs. time)
  • Dynamic Shear Rheometer (Creep and dynamic experiments)
  • Stress Relaxation
  • Creep Experiments
  • SHRP Shear Frequency Sweep for Mixtures
This software computes the Discrete Relaxation and Retardation Spectra.

© Abatech 2009