Fatigue and vibration 2

[Irwin]

I had seen many-many S/N curves which are very usefull for life estimation. My problem is the next: <br>
In these diagram we loose the freqency information. What is the situation if try to make a test serious on the eigenfreqency? Will we get a point on the S/N curve or this is a total new situation?

 

[tomb]

Ask Dr. Balachandran at the the university of maryland, college park campus. Call the general number and they will connect you with him. He is in the mechanical department.

 

[hamilton]

We have conducted constant amplitude fatigue tests on welds at several frequencies and found that the results were independant of frequency over the range 1 to 100Hz. What frequency range are you interested in?

 

[Irwin]

This frequency range is correct for me. <br>
What is the situation whith composite material in this range? (I heard, some composite material's temperature inreases and the material itself changes.)<br>

 

[goodvibes]

ERWIN,

The S/N curves show the cycles to failure (or frequency of applied load) on a test specimen, i.e, an Aluminum rod or plate sample. Which curve you use depends on the nature of the applied load (load ratio R). For example if you subject a test specimen to a fully reversed load (from full tension to full compression at a frequency of 70 Hz, than in 10 hours of testing you would have accumulated 70*10*60*60 = 2,520,000 cycles. So the Frequency on the S/N curve really applies to number of load cycles. If you know the freq of the applied load you can predict the fatigue life; but beware, there are many other factors to consider, such as stress intensity factors.

I hope this was helpfull, becuase I'm not exactly sure what you are asking?

 

[tomirvine]

The following textbook has some good examples for vibration fatigue calculations:

Dave Steinberg, Vibration Analysis for Electronic Equipment, Wiley-Interscience, New York, 1988.

Sincerely, Tom Irvine

http://www.vibrationdata.com

 

[manfred127]

Frequency has no effect on S/N curves .The main factors which can have an influence are stress concentration factor,coating and fretting corrosion
At the eigen value the most important factor to take care about is the damping of your system
You can easily overtake elastic(yes elastic not fatigue!) limit of your system with low damping even with small excitations .I have already experienced this on a resonator
It's funny but not very efficient.