How can I use Frequency Sweep DMA data to define Prony Shear series at ANSYS WB?

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Scott Grindy

I believe your question is effectively about how to compute the discrete relaxation spectrum from oscillatory shear data. I suggest you start with Baumgaertel & Winter, Rheologica Acta, 1989, Vol 28, p 511.

Alternatively, there is a free MATLAB program which will effectively perform the same task: https://www.mathworks.com/matlabcentral/fileexchange/40458-respect

I'm not familiar with ANSYS, so I can't help you with that part.

Gerges Youssef

Hi Scott,

Thank you very much for your help.

Based on the test I did for a rubber sample (DMA frequency sweep at a constant temperature at shear mode), I want to extract the viscoelastic model parameters according to Prony Shear Relaxation (relative moduli and relaxation time (in seconds).

The experimental data I have is storage modulus, loss modulus, amplitude and strain % VS. Frequency.

I am not sure that the program you sent will do what is needed.

Please advise.

Best regards,

Sure it will - you might have to play with it a bit if your material has a non-zero modulus at infinite times. The program can compute the discrete relaxation spectrum from your storage & loss modulus, which is quite nearly the Prony Series representation of the relaxation modulus. If you need some review of the relation between relaxation modulus, storage & loss moduli, and the relaxation spectrum I'll refer you to the book "Viscoelastic Properties of Polymers" by J.D. Ferry.

Hello Scott,

I have almost no exposure at all in using Matlab. Can you help me in brief step how to get one of the data sets shown in the attached files using a frequency sweep DMA test results either using the matlab freeware respect, or using any other tool?

Your help will be highly appreciated!

I can't show you exactly what to do, unfortunately. If you have more questions, you should consult the "README.pdf" file located in ReSpect download, or contact the authors of that package. You may also find their article helpful: A Computer Program to Extract the Continuous and Discrete Relaxation Spectra from Dynamic Viscoelastic Measurements, Appl. Rheol. 23 (2013) 24628.

OK. Thanks for your help.

Ahmed Benalla

Hi Gerges

did you fix this problem?, i have the same question.