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Viscoelastic material model in abaqus-am i taking the correvt approach

Hi all,

I have been trying to gain an understanding of representing a viscoelastic material in abaqus. To do this i have been trying to represent polypropylene using data obtained from creep curves found in literature (attached). To now what i have been doing is the following: Note i am using Abaqus 6.7

In material manager: selecting Elastic-inputting Instantaneous Youngs Modulus, E, Poissons, v, (E=1.8GPa, v=0.4) and setting the moduli time scale to instantaneous. And Viscoelastic-Domain:Time, Time=Creep Test data and inputting Shear Test Data

Shear Test Data obtained as follows:

1. From the instantaneous youngs modulus, E and poisson's ratio, v, obtaining the instantenous shear modulus, G0=E/(2(1+v))

2. Picking a certain stress, and probing values of strain against time (from attached creep curve):
3. Calculating:
Creep modulus, E(t)=stress/strain(t)
Shear Modulus, G(t)=E(t)/(2(1+v))
Shear Compliance, Js(t)=1/G(t)
to finally obtain "Normalized Shear Compliance", js(t)=G0.Js(t) as requested by Abaqus. I guessed the "Long-term normalized shear compliance or modulus" based on the calculated data.

To test this inputted material property, I perform creep tests on a 1m x 0.5m model and visualise the results. With these results i try to recreate the creep curves.

The only curve that ever correlates is the curve i took values from. I was hoping for some guidance on the matter if anyone could provide it. Maybe i have been approaching the problem all wrong? What should I be doing?

Image icon polypropylene.jpg311.23 KB
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