Measuring Viscosity of Materials with Dynamic Modulus

[gkiverm]

I understand that the dynamic modulus of a material is measured by inducing a sinusoidal force and measuring the strain response. Usually one gets a value for the storage and loss modulus. However, I don't understand how one would "quantify" how viscous a material is. I know a viscous material (less elastic) has a higher loss modulus and a lower storage modulus. But is there a certain ratio of the two variables where one considers a material mostly elastic or mostly viscous? I guess it would be easier if I can get a value for the dynamic modulus for some common materials. In addition, I understand the dynamic modulus is dependent on the frequency. So which frequency is common one to use when judging how viscous / elastic a material is?

 

[Chestermiller]

The ratio of the loss modulus to the storage modulus is the tangent of the phase angle. This is a measure of the ratio of viscous response to elastic response. The behavior varies with frequency. At very high frequencies, elastic behavior dominates, and at very low frequencies, viscous behavior dominates. So, in practice, it all depends on how rapidly the polymer is deforming in your actual process.

Chet

 

[gkiverm]

So if the tangent of the phase angle varies as frequency varies, is there a standard frequency people use to measure the tangent of the phase angle to compare the viscoelasticity of different polymers?

 

[Chestermiller]

So if the tangent of the phase angle varies as frequency varies, is there a standard frequency people use to measure the tangent of the phase angle to compare the viscoelasticity of different polymers?

No.

Chet