How to calculate internal stress of a horn in an Ultrasonic System

[packeng]

Hello,
We have a 30KHz ultrasonic system (Converter, booster and horn) for plastic welding. The horn has cracked for fatigue several times and we don’t know why.

We are trying to calculate the internal stress but can not find the way to get it.

We have been working with the Professional inventor Program with the Stress Module to make modal analysis and we have found the modal frequencies and the amplitudes of the horn, but can not find the internal stresses.

Can anyone help us on this??

Thank you very much in advance,

 

[spongebob007]

You need to solve the complete equation (harmonic response analysis).

Modal analysis only solves:

m*(d2x/dt2)+k*x=0

Frequency response solves:

m*(d2x/dt2)+k*x=F(t)

Modal analysis only gives you frequency, mode shape, and relative nodal displacements.

Harmonic response analysis will give you the stresses. Not sure if you can do that with the software you are using. Is it a low end program? Most of the "lite" FEA programs will only do modal analysis and static stresses.

 

[packeng]

Thank you spongebob007!
We are using Autodesk Inventor Professional 2010, do you recommend another software that could do the Harmonic response analysis?

We could have the possibility to get it.

 

[spongebob007]

Most full FEA codes such as ANSYS,NASTRAN,ABAQUS, etc can do harmonic response analysis. They will be more expensive than what you are currently using.