Bob Crantz wrote:

How about sending an acoustic pulse along the rod rigging the same as a time
domain reflectometer works. The pulse speed is a property of material and
tension and the reflectance a function of acoustic impedance. Cracks would
raise the impedance. The cracks could be located along the length of the rod
by simply applying the pulse signal at one point.

Sounds good to me, I don't belive tension (or compression) has anything
to with the speed of transmission in a solid.

Cheers
Marty