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?