Can damping ratio be calculated without experiments or damping coefficient?

[hawkish_man]

I’m familiar with the experimental methods to determine the damping ratio of a material, but I’m wondering if there’s an alternative way to calculate it using mechanical properties alone.

For example, stiffness (K) can be derived using the formula K= (A*E)/L, where A is the area, E is the modulus of elasticity, and L is the length. I’m curious if there’s a similar approach for damping ratio? Assume we don't know the Damping Co-efficient or factor.

And, if you don't have the resources to conduct experiments to determine damping, are there any sources like MatWeb where we can find the damping ratios for materials?

Thanks

 

[GregLocock]

You've assumed E in your stiffness example, which has to be measured (well OK you can calculate it if you measure some other stuff instead). No there isn't a way of calculating damping for a structure, that I know of. If you have a large discrete damper in the system (eg TV damper) then yes you can estimate the overall damping of the system, but again the characteristic of the damper will need to be measured.

Cheers

Greg Locock


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[hawkish_man]

Thanks for the reply,

Okay, damping needs to be measured. But are there any databases or websites with approximate damping ratios for different materials?

Thanks

 

[3DDave]

Google?

https://help.solidworks.com/2016/english/solidworks/cworks/r_viscous_damping_ratios.htm

 

[hacksaw]

Clarence Zener, formulated a quantum mechanical model of elastic damping in 1940, and offered experimental evidence to support his calculations.
Damping has to do with the nanometer scale imperfections in the material, that are affected under stress-strain conditions.

 

[hawkish_man]

Thank you for the information guys.

 

[GregLocock]

Roughly speaking 0.1% for homogenous steel parts, 0.3% for cast iron, more for bolted assemblies, much more for complete items.

Cheers

Greg Locock


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[GVDR]

Damping is not additive, and not linked to stiffness or mass in general. You will thus not be able to easily setup a guess without assumptions.
That said, if you are working with loss factors in structural dynamics, you can use the Modal Strain Energy assumption. It states that the synthesized loss will be the sum of the components loss (maybe from material data) weighted by their strain energy ratio.
Beware that in assemblies most damping comes from connections and fastened areas, so that an assembly gets more damping than free components. Energy ratios can be challenging to estimate at interfaces.