Authors: Matthew G. Smith & Manlio Tassieri
University of Glasgow
Date: 22/06/2022

Install: Run I_Rheo_App_Installer.exe to install I_Rheo.
	 The Installer will automatically install MATLAB runtime.
	 NOTE: You will need administrator rights to run the MATLAB Runtime installer.

Aim: This program is designed to evaluate the frequency-dependent materials' viscoelastic moduli via the ratio between the Fourier transform of the time-dependent force and indentation functions.

How it works: 
The app analyses stress relaxation measurements performed by means of any generic indenter with a spherical tip of known diameter. 
The app will automatically identify the peak force achieved during the initial indentation and before the start of the stress relaxation.
It rescales the time axis of both the force and indentation functions and plot them on the top-right "Relaxation Data" graph.
The user then has the opportunity to cut the long-time behaviour of both the above functions by choosing a cut-off time. 
Additionally, the user can choose to smooth the data and, if required, pick a time at which to start the smoothing process. 
The Relaxation Data which may have been smoothed or cut will be used during the calculation of the viscoelastic moduli plotted on the "Complex Modulus" graph.
The user can then download the Relaxation Data used for the conversion and the Complex Modulus.   
  

The steps are:
1) Import your force and indentation in the form of a .txt file with 3 columns: time (column 1), force (column 2) and indentation (column 3).

2) Choose the units of force and indentation.

3) Input the tip radius and poisson ratio (default = 0.5).

4) Input the value of: the force at time = 0, the indentation at time = 0, the gradient of the force at time = infinity, and the gradient of the 
    indentation at time = infinity (default = 0 for all of them).

5) Choose whether to perform the oversampling of the function or not (default = Off); if On which interpolation function to use (default = Spline).

6) Choose whether a cut off time (default = Off) is needed and what this time should be. 
Note the app automatically detects the first cut off time based on the peak force value, and uses this to scale both the force and indentation signals initially.

7) Choose whether to use smoothing on both the force and indentation functions before being Fourier transformed. 
**Special attention must be taken when using the smoothing function as it may not accurately smooth the data at short times**. 
Use the "Smoothing Time [s]" input to change the time at which smoothing takes place.

8) Use the "Run Fourier Transform" button to calculate the viscoelastic moduli. 
Note that: (1) this could take several minutes if oversampling is selected; (2) if any parameter is changed, you will need to press this button again to update the viscoelastic moduli.

9) Download the viscoelastic moduli in the form of a .txt file with three columns: Frequency (column 1), G' (column 2) & G" (column 3).

10) Download the Scaled Time Data in the form of a .txt file with five columns: Time (column 1), Unscaled Force (column 2), Scaled Force (column 3), Unscaled indentation (column 4) & Scaled Indentation (column 5).