Hi Hasan

The easier approach to fit a viscoelastic model in Abaqus is to perform a creep or relaxation test. 

You can upload you experimental results directly into Abaqus to fit a Prony series with the viscoelastic parameters of your material (Use the "Evaluate" function in the material manager window).

From uniaxial compression test it might be possible to fit the viscoelastic parameters but I guess it will require  testing at different strain rates.

Hope this helps.

BR,

David

Hi David

Thank you for you reply.

I carried out in lab the uniaxial creep test at a certain stress. the lab results give the time vs %strain. I did calculate the the Normalized shear compliance js(t) through this procedure:

Creep modulus, E(t)=stress/strain(t)

Shear Modulus, G(t)=E(t)/(2(1+v))

Shear Compliance, Js(t)=1/G(t)

js(t)=G0.Js(t)

G0 used is the value of creep modulus at the first cycle.

the result for this calculation were as follow:

Pulses Strain % Creep Modulus E(t) Shear Modulus G(t) Shear Compliance Js(t) Normalized shear comliance js(t)

2 0.468481 64036748.56 23717314.28 4.21633E-08 2.7

4 0.543464 55201448.49 20444980.92 4.89118E-08 3.132150077

6 0.588486 50978273.06 18880841.87 5.29637E-08 3.391625701

8 0.617264 48601570.8 18000581.78 5.55538E-08 3.55748216

10 0.640136 46865041.18 17357422.66 5.76122E-08 3.689300527

20 0.702866 42682388.96 15808292.21 6.32579E-08 4.050832798

40 0.755285 39720105.66 14711150.24 6.79757E-08 4.352939607

(THEY ARE NOT ALL THE DATA)

I used the last column of the data to be used in ABAQUS: Elastic: viscoelastic--- frequency domain--- creep test data ---- shear test data--- and then implement the two columns there but unfortunately after running the job it says "No convergence for any order n for the viscoelastic shear test data" and then analysis aborted.

Do you know what is the problem?

thanks for cooperation in advance.

Hasan

Hasan. Why are you using frequency domain? If you got from your lab test time vs strain why not to use directly time domain?

Also, to obtain the viscoeltastic parameters you should input the Young's Modulus. I guess you will be using the instantaneous modulus instead of the long term modulus so make sure that you are selecting "instantaneous" when you define the young's modulus (By default the modulus is set on "Long term" ).

Hi Hasan Al-Mosawe 

I wil like know if you could help me because I have the same problem that you...

I´m Trying to model the behavior of asphalt mixtures in abaqus and I have the uniaxial test data form Creep Test. I was trying to do the procedure that you describes  and unfortunately the software says the same message...Could you explain to me

My other question is...How i can obtain the long term modulus from Data?

thanks

Hi Liosber

Actually I tried the different opinions suggested by other people in this question but unfortunately it didn't work.

then I tried to get the relaxation data from the creep data and implement them in ABAQUS.

The paper attached shows different ways of converting the creep data to relaxation data, I used the Quasi-Elastic Interrelationship and it works.

The long term modulus was suggested to be the modulus in the last cycle.

Thanks to other people for their comments and suggestions.

Hello Hasan Al-Mosawe

Yesterday night i saw one for a master degree of ENZWEILER, J.L. (2013). CARACTERIZAÇÃO DE MATERIAIS VISCOELÁSTICOS COM APLICAÇÃO DE SÉRIES DE PRONY E ANÁLISE POR ELEMENTOS FINITOS. UNIVERSIDADE FEDERAL DO PARANÁ, 115 p.

and there its explain one procedure that I´m tested and i think that its useful. If you want you can read and tell me what do you think about it.

Guys, 

I did the procedure we discussed and I am getting very strange creep curve (photo attached)

any idea?

Hassam 

I cannot see the attachment. Can you increase the quality of the image?

is this better?

Hi Tarkes

attached is a sample of the data

thanks

Yes

Dear Tarkes Dora ,

From Your Answer

FYI Js(t)=1/G(t) is wrong

G(t)*J(t)