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Error in getting Prony parameters in ABAQUS for visco material from creep test data from nanoindentation


ess_987
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Hi all, I am trying to model polycarbonate in ABAQUS through the creep test data method, so far when I run my model I get the error: THE MAGNITUDES OF SOME OF THE DEVIATORIC RELAXATION COEFFICIENTS FOR VISCOELASTIC MATERIAL ARE UNREALISTIC. THE MAGNITUDE OF EACH COEFFICIENT MUST BE LESS THAN ONE. I am not sure how to solve this, it must be an error in my js(t) values so this is the method I followed, please tell me if I have done something wrong:

1. Get load, displacement, time values from nanoindentation test

2. I found an equation to get the creep compliance Js(t) = contact_area / [(1-poisson_ratio)*LOAD*tan(theta)]

3. For my berkovich indenter, contact_area = 24.5*h^2, theta is 71 degrees

4. Next I have to normalize Js(t) to obtain js(t) which is required by ABAQUS, so I divide all values of Js(t) by the value at t=0 i.e.: Js(0)

 

Some of the values I have input in ABAQUS are as follows;

 

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