Pipes equivalence in a fatigue test

[TeeAr]

Hi there,

hope everything is fine and wish you a great year.

Please, I am writing you for following issue.

In the past a copper pipe, having a certain diameter, let's call it D, and thickness, t, has been tested in a fatigue vibrational test.
The pipe was fixed at the ends to a metal sheet.

This pipe, let's call pipe1, has passed the test.

I decided to change this pipe with a new one. the material and mechanical characteristics of this second tube are identical to the ones of pipe1.
the new one presents
- lower diameter, let's call it D1
- lower thickness, let's call it t1.

This second pipe, pipe2, has not passed the test. There has been some fractures.

Please, do you know if there is any formula that help me to compare pipe1 to pipe2 concerning vibrational and fatigue resistance ?
The aim would be to determine the new t1 in order to pass this test.

Many thanks !

 

[desertfox]

Hi TeeAr

I would start with a calculation of the natural frequencies of both pipes, if the length of both pipes were the same and the only change was to the outer diameter and thickness of the pipe wall then both pipes will have different natural frequencies.
Checkout the links:-

http://www.roymech.co.uk/Useful_Tables/Vibrations/Natural_Vibrations.html

http://www.vibrationdata.com/tutorials2/beam.pdf

The second link on page 46 calculates the natural frequency of a pipe.

desertfox