I want to find the value of two constants from an equation with two variables

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I am trying to find the values of the constant elastic modulus (E1) and viscosity modulus (eta1) from the Kelvin creep recovery equation. The data points of strain and time needs to be exported from an excel file(given) and the value of constant stress is given as 6 nN.
The equation being used is: here sigma(0) is the constant stress(given) and epsilon is the variable strain(data points given)

Accepted Answer

Star Strider
Star Strider on 3 Aug 2021
To estimate the initial parameters for this, since is known, the asymptote as will be , and that gives a way to estimate E. Here, is essentially a time constant, so if you can calculate the time at 0.6 times the asymptote (use interp1), you can estimate the initial value of η as well, having already calcualted E.
Use those as initial values with the code you already wrote.

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More Answers (1)

darova on 3 Aug 2021
Try fit
  1 Comment
Nidhi on 3 Aug 2021
@darova Hi. I have never previously used "fit" and am quite new to MATLAB. Can you kindly, please show me how I can implement "fit" in this case.

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