RHEA (Rheology Analysis)
RECENT UPDATES
The RHEA™ Software User friendly analysis RHEA™ has been
specifically developed for engineers working in rheology needing a
rapid analysis procedure. Mastercurves 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 viceversa. The shifted master curves are fitted using
a modified nonlinear MarquadtLevenburg 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 viscoelastic 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.
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.
The
second plot illustrates the resulting master curve with the mode
contributions (this is an option that the user chooses to display).
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).
The
second plot illustrates the resulting master curve G* and phase
angle.
The
final plot shows the same data set transformed to J(t) using the
spectrum analysis.
3. Asphalt Mixes
The plot below shows results developed from a the Superpave
Shear Tester expressed as a frequency sweep.
This program has been developed as a general tool for performing
rheological analysis of a wide variety of materials that behave
according to linear viscoelastic theory.

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.
