# Time domain testing of viscoelastic material in Abaqus

Dear All;

Hope you are having a wonderful day. I am currently working on a project which is related to developing a user material interface for a viscoelastic material, for testing it I have to compare it with the existing built-in Abaqus model. Since my working is on small strain deformation I am using time-domain in Abaqus. I have the bulk modulus of the material "K", Young's Modulus of the Material "E", the shear moduli for Prony series "mu1", "mu2" and "mu3" and the relaxation times "tau1" AND "tau2". I need to convert this data into Abaqus input mode which so I need "g(i)p", "k(i)p" and "tau(i)". I know that according to equations:

K=E/3(1-2v), mu(infinity)=E/2(1+v) and mu(i)=mu(infinity)*g(i)p

will give me the values for Poisson's ratio "v" and values for "g(i)p" but can someone please guide me how to find the bulk moduli and relaxation times. I do not have test data for the material unfortunately and I have been trying to locate any conversion formulation from books or papers.

Thanking you in advance for helping.

Best Regards;

Asim Gillani

### Look up the BAQUS example 2.1

Look up the BAQUS example 2.1.1
'Viscoelastic rod subjected to constant axial load'

Subscribe to and seek assistance from the ABAQUS mailing list
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Good luck

Frank

### Thank You

Dear Sir;

Thank you so much for your kind response. I will surely join the blogs and groups mentioned.

Best Regards;

Asim Gillani

### ABAQUS example 3.1.1

Dear Sir;

I have read the example you mentioned and it does explain how to convert certain data available for UMAT to ABAQUS input data but it does not give information on finding bulk moduli k(i)p, I have searched on different forums and what I have found is that if Poisson's ratio is 0.49~0.5 the k(i)p values are zero (not mentioned) which is true for the example listed. but if the Poisson's ratio is not within this range then how do we calculate k(i)p from conversion from above-mentioned data. Further, I have tried searching for the reference listed in the example "Collingwood et al. (1985)" but I am unable to find it. Could you please kindly provide guidance in this matter. thanking you in advance.

Best Regards;

Asim Gillani

### I also wanted to get this

I also wanted to get this manual into my hands. The german Abaqus HQ forwarded to me an e-mail from Abaqus World HQ:

"The bench mark problem is simply a clone of the first example problems in the second volume of TEXVISC user's manual. Besides the example problems, the manual only describes how to use the program. There is nothing noteworthy to make a copy. TEXVISC is a 2D finite element program for thermal and mechanical analysis."

So, forget it.

It is bizarre to declare a simulation correct simply on the grounds that some other FE program is declared correct.

Consult the forum.

### Comparison of Abaqus built in viscoelastic material model & UMAT

Dear Sir;

I asked regarding an issue I was having with the conversion of a set of values either from Abaqus input or UMAT input. I figured out how to convert a model into Abaqus inputs if K(bulk Modulus), mu1(spring coefficient of spring element), mu2(spring coefficient of first Maxwell element), mu3(spring coefficient of second Maxwell element), tau1(relaxation time for first Maxwell Element) and tau2(relaxation time for second Maxwell Element).  I converted these into ABAQUS time domain inputs, E(Young's Modulus, E=mu1+mu2+mu3), Poisson's ratio (v=(3K-E)/6K), g1p, g2p, tau1(Abaqus) and tau2(Abaqus). the results I obtained are quite better but still, there is a difference of more than 2 MPa in stress. the plots are near to each other but there is some gap between them. My question is how much error is allowable in a comparison between a built-in Abaqus model and UMAT developed further if you want I can attach my working in an email to you.

I would be very thankful for your kind help in this regard.

Best Regards;

Asim Gillani

### Comparison

Dear Asim

I would be glad if you forwarded your analysis and code to me.

You can contact me privately here.

Regards

Frank

### how do i attach a file

I am trying to attach some files for your review but I am unable to do so in the reply will I have to make a new blog entry?

### how do i attach a file

I am trying to attach some files for your review but I am unable to do so in the reply will I have to make a new blog entry?

### PM

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