Doubt in input of experimental data for viscoelasticity

**somaraju** · 2010-09-11, 02:27

Hi Mr.Jorgen and all members
I am working on material "Polypropelene" . software: Ansys

I am considering Viscoelastic property.In that the experiment (i thought)required to be done is either 1 or 2
1.Tensile test relaxation data (strain is fixed and stress varies)
2.Creep Test(stress fixed strain varies)
CASE 1:
If I consider the relaxation data i will calculate the shear modulus by dividing modulus by 3
Using this data i want to apply in PRONY (shear response) in Ansys.

I know only this approach suggest me regarding other approaches(Maxwell,curve fitting)
CASE 2: I dont know how to approach this in Ansys

Please Help me in choosing the right way.

**Jorgen** · 2010-09-12, 08:46

The easiest way is to use CASE 1: a stress relaxation experiment.

Note that PP is only linear viscoelastic at small strains.

-Jorgen

**somaraju** · 2010-09-12, 08:58

Thank you jorgen
Case 1: Yongs modulus and poissons ratio as input parameters,
case 2: Giving young modulus, poissons ratio and prony series data for pp at ROOM Temperature
The results from case 1 and case 2 will it be same or not
Please explain me.

**somaraju** · 2010-09-14, 13:57

hi
i used the ptfe material. I have taken tension relaxation data avaialable in this site .I claculated the shear modulus and used the curve fitting technique for viscoelastic(input is shear modulus versus time). I applied a displacement of 2 mm( as load) and got the results.The result obtained from taking viscoelastic and only elastic(youngs modulus,poissons ratio) giving same answer . This should not be happen according to my knowledge ......please suggest anything

**Jorgen** · 2010-09-14, 18:55

You are right that a linear elastic material model should not give the same result as a linear viscoelastic material model. They only give the same results if the viscoelastic parameters are selected such that the viscous effects are not influencing the results.

-Jorgen

**somaraju** · 2010-09-15, 00:11

In the data i considered(taken from your site) is at room temperature i think so.
I am thinking that if i do the experiment at 45 to 100 degrees then the data should be incorporated .Then the results will differentiate i think so the viscous effects come into picture
i have another doubt that time history pricessor come intoexistence or not
Is the load application gone wrong or any other way of giving .............please suggest me