Tutorial Creep Application

This short tutorial shows how to load the bundled creep examples and inspect the main creep-compliance views. It does not require fitting a theory.

Load Creep Data

  1. Start RepTate and create a new Creep application.

  2. Open one of the example files in data/Creep:

    • Maxwell.creep

    • CM3_Creep.creep

    • CM3_CreepRecovery.creep

    The Creep application reads text files with the .creep extension. The file parameters include the applied stress and may also include parameters such as Mw and T. The data columns used by the application are time t and strain strain.

Inspect Views

Use the View selector to switch between the creep representations:

  • gamma(t) plots the measured strain as a function of time.

  • log(gamma(t)) plots log10(t) against log10(abs(gamma)).

  • J(t) plots the creep compliance, calculated as \(J(t)=\gamma(t)/\sigma_0\), where \(\sigma_0\) is the applied stress file parameter.

  • log(J(t)) shows the same compliance on logarithmic transformed axes.

  • t/J(t) plots time divided by compliance, which is useful for inspecting the approach to steady viscosity.

The i-Rheo views transform the compliance data to obtain \(G'(\omega)\) and \(G''(\omega)\). When one of these views is selected, RepTate shows extra controls for the steady-state viscosity and the time range used by the transformation; the oversampled i-Rheo view also shows the oversampling control.

Fit retardation modes

  1. Select a single creep data file in the data set. The Retardation Modes theory is initialized from the first active file, so keep only the file you want to fit active when setting up the theory.

  2. In the theory selector, choose Retardation Modes and create the theory. The initial modes are distributed logarithmically between the smallest positive time and the largest time in the selected file.

  3. Use the mode spinbox in the theory toolbar to change the number of modes. The theory documentation recommends roughly one mode per decade as a useful starting point for modes intended for flow simulations.

  4. Click Calculate to evaluate the current parameters, or Minimize Error to fit the instantaneous compliance logJini, terminal viscosity logeta0, the time range logtmin/logtmax, and the mode compliance values logJ00, logJ01, etc.

  5. When the mode markers are visible, drag the yellow points to adjust the mode compliances. Dragging the leftmost and rightmost modes changes the fitted time range.