Cliff Manzke wrote:

Paul's question:

Can you figure out what it is for a tension bolt with 30 foot
pounds of torque? Don't have one in front of me but I would
guess it is 12 inches long about 3/8 inch in diameter.

Answer:

For a simply supported solution, the first mode will be 415 Hz.

For a fixed end solution (i.e., both ends clamped) the first mode will be about 2.3 times higher or 954 Hz.

A bolt head is not as "clamped" as you might think so the real solution should be something lower than 954 Hz, perhaps about 800 Hz.  In any case, the frequency is quite high so I don't think it's a problem. HOWEVER, note what I said earlier about "higher harmonics" of the engine forcing frequency.  6000 rpm X 4th harmonic = 800 Hz = problem!

Cliff Manzke

Bad news. I am surprised there is enough energy in the second and fourth harmonic to fatique
a bolt.

Paul Lamar
 
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