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

The analysis in RHEA begins with the use of the time-temperature superposition principle in order to align the test isotherms into a single master-curve. To form the master-curve, it is necessary to determine the shift factor that when applied to each isotherm temperature, allows to convert the test measured data to its equivalent at a predetermined reference temperature. RHEA’s considered shifting procedure is the one defined by Gordon and Shaw (1994).  

Following this procedure, several other shifting methods are also determined in parallel, such as the Arrhenius, WLF (Williams-Landel-Ferry) and the Kaelble modification of the WLF model. After the data has been shifted various model fits are attempted and applied. These include the relaxation/retardation spectra (often referenced as Prony series), and functional forms such as the Christensen-Anderson model (1992). RHEA's display of its analysis will always include both the graphic and numerical forms on each available option.

The definition of the discrete spectra allows calculating the properties that the tested material will possess at any temperature and loading frequency within the accessible region of the test.

Among RHEA's other features include the determination of:

  • Complex viscosity

  • Phase angle and Black's space

  • Relaxation and retardation spectra

  • MEPDG master-curve and shift factors

  • Oberst beam damping simulation

  • Glover-Rowe parameter

  • DTc from stiffness and m-value

  • Rheological index 

  • Steady state viscosity vs. temperature

The data that RHEA considers for its analyses results from dynamic and transient tests. The output of these tests is materialized in the form of raw data files that RHEA is able to easily convert to its own native format, the tTd files. RHEA can read any number of tests simultaneously and merge the information in one single tTd file. The supported formats include those produced by several equipment manufacturers, such as Alpha-Technologies, Anton-Paar, Bohlin, Interlaken, IPC, Rdall, Malvern and TA Instruments.

 

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