## General Mechanical

Topics relate to Mechanical Enterprise, Motion, Additive Print and more

#### Modal analysis

• Cri1994
Subscriber

Hi everyone,

I'm doing modal analysis about a simple component. the component is a bar ( 40X16X500 mm).

I have a question for you.

The modal analysis launched with a bar in steel(2,512Kg) gives me these modes: 51,914 Hz, 128.95 Hz, 323Hz.

The modal analysis launched with a bar in magnesium alloy ( m=0,576Kg) gives me these modes: 52.337 Hz, 130,08 Hz, 326,43 Hz.

I think that it is non normal. What could be the problem? The materials settings?

Thanks a lot for your time

Cristiano

• peteroznewman
Subscriber

Modal frequency is proportional to sqrt(K/M).

K is proportional to Young's Modulus.

Ratio of Steel to Magnesium Young's Modulus is 2e11/4.5e10 = 4.44

Ratio of Steel to Magnesium Density is 7850/1800 = 4.361

Expected Ratio of Modal Frequency Steel to Magnesium = sqrt(4.44/4.361) = 1.01

This tells me that the modal frequencies being almost the same is expected.