On Wed, 19 May 2021 17:42:41 -0400, "Jim Wilkins"
wrote:

"Joe Gwinn" wrote in message
.. .

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:

[snip]

Like "Fluid-operated vibration test exciter" to John Dickie, patent
US2773482A. This is basically a siren driving a shuttle piston back
and forth. If the shuttle piston is prevented from moving, it will
generate a cyclic stress. The addition of a dead weight to this
allows the cyclic stress to ride atop a static stress.

Joe Gwinn

----------------------------

I considered an oscillator-based solution but didn't suggest it because they
may require specialized instruments, dataloggers, digital storage
oscilloscopes and spectrum analyzers, to test and debug. It's much easier to
test a system that can be stopped or run slowly.

In the patent reference above, the oscillation cycle is controlled by
an external "variable speed motor" of unspecified kind, designated is
item 25 in the figures and accompanying text.

If the motor runs slow, so does the oscillation cycle, in direct
proportion.

Joe Gwinn