Influence stress on natural frequencies

[JeroenDevos]

Hi,

for my internship, I'm verifying the static and dynamic behavior of a milling machine. I was wondering what the influence of stress can be on the dynamic behavior. I'd say that a system under stress has higher natural frequencies. In this way, one could stress up a structure to avoid that dangerous natural frequencies occur in the working area of frequencies.
Is stress (prestress the structure) used in real life to place the natural frequencies. If not, why not. If yes, can you give me more information about it.

Has anyone got some tips about this topic,
thanks in advance!
Jeroen

 

[eromlignod]

External stress obviously changes the natural frequency (think of a piano string). I'm not sure how practical it would be to apply this to machinery though.

Don
Kansas City

 

[EdDanzer]

One reason to not pre stress a machine tool is that loads can be multi directional. Any structure will deflect when loaded, so a preloaded item will be less rigid when loaded in the pre stressed direction. This will make the machine deflect one way more than another, and could cause more different frequency vibrations.
I don’t think there is any substitute for stiffness in a structure. Some machine use mass, but with some types of loading this will not work.
When doing FEA on a machine tool structure, deflection should be the primary concern, and should be verified after assembly.