maxwell / voight models for polymers..can someone check this...?

(Xposted to sci.polmers)

Tutorial question was given.....

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The Creep response of a polymer corresponding to a load application for 100s can be described by a Voight Model where the Elastic element = 2GPa, and the Viscous element = 100 x10^09 Ns/m^2. If the Maxwell model has viscous element = 200 x10^09 Ns/m^2

Find the value of the Maxwell elastic element.

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I have the solution below.....but I'm not sure that I'm correct. I have, for Maxwell, Epsilon = (sigma / E) + (sigma / Viscosity).

I think it should be Epsilon = (sigma / E) + (sigma^dot / Viscosity). where sigma^dot is 'stress rate' rather than stress..?

can anyone clarify for me?? If it is 'stress rate' rather than stress' how do I calculate this - is it as a function of the time period??)

my working is this:

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Strain Rate for the Voight model is found from:

Epsilon = (Sigma / E) (1- exp (-E * t)/Viscosity))

Epsilon = (Sigma / 2 x10^9) (0.864)

Epsilon = Sigma * 0.432 x 10^-9 [eqn 1]

For the Maxwell model

Epsilon = (sigma / E) + (sigma / Viscosity)

Substituting eqn 1 gives

Sigma * 0.432 x 10^-9 = (sigma / E) + (sigma / Viscosity)

Div thru by Sigma to give

0.432 x 10^-9 = (1 / E) + (1 / 200 x10^9)

1 / (0.432 x 10^-9 - 5 x10^-12) = E

E = 2.34 x10^9 Pa

E = 2.34 GPa

thx Simon.