"Jim Wilkins" writes:

"Richard Smith" wrote in message ...
...
You asked about this device.
I'll share with you
http://www.weldsmith.co.uk/tech/fatg...hyd_inner.html
It's an idea for a metal fatigue test, particularly of welds.

So in this rig, the sample is inaccessible, inside the hydraulic
cylinder immersed in the hydraulic fluid.

For the advantages you get, the disadvantages are "nothing".
This test could be running for days to 10's of days, by the way.
It's "high stakes".
---------------------------

You might be able to significantly reduce the 80KW power demand if the
pressure source is a small flywheel-driven piston built into the fixed
end of the cylinder to minimize flow friction loss, that absorbs the
pressure energy as it retracts. You'd add oil/bleed air until a
pressure sensor signal peaks at the desired pressure.

This could require some custom machining and knowledge of using an
oscilloscope. Are those acceptable for you?

When I was in the automated testing business we had to figure times
for high count operations such as testing each cell on a memory chip
wafer, often in conversation without a calculator. There are 86,400
seconds in a day. 1 million seconds (cycles?) is 11.57 days. A
micro-year is 31.5 seconds. 1 US billion (10^9) seconds is 31.7 years.

https://www.youtube.com/watch?v=hj7LRuusFqo

Exactly so.

I have already done these calculations for my "beam configuration"
fatigue test.
Static version of it - tensile test
http://www.weldsmith.co.uk/tech/stru...t_testrig.html

The benefit you have there are the highly predictable Euler-Bernoulli
beam calculations for long sections.
I found one fixed stroke actuator would cover every need.


The problem with the "hydraulic inner fatigue test" is it is difficult
to know with much accuracy how much hydraulic oil it is going to take
per stroke to reach the intended force on the sample.
The end pistons seem to be the design challenge. Flexing. Cylinder
analysed by "hoop stress" no problem.

Also - adjusting it so you can arrive at different forces...
Because you need to explore the shape of the fatigue "S-N curve".

That's why took thought of servo-hydraulic.
With "catalog" equipment you could quickly get started.
Connect it up and off you go.
You'd probably use a pressure transducer and servo valves, wth digital
logic linking them. In reality. As the equipment would be already
there and familiar.