Lifetime of a torsional support?
Lifetime of a torsional support?
(OP)
I just had a disagreement with a colleague on a mechanical issue which frankly neither of us is competent to give a definitive opinion on. There is a torsional support for a mass, the mass being held at the top and bottom and rocked to and fro by some external force. The details are not important.
My colleague argues that provided the torsional support is not taken past its elastic limit it will have an essentially unlimited life. My argument is that even for small motions it will fail eventually due to fatigue or hysteresis. Obviously the support may eventually deteriorate due to decomposition of the support, but not withstanding that I would expect that after a few years of rocking backwards and forwards at a 50Hz rate it will break. I suspect that the support is some sort of rubber/plastic/elastomer but the same effect presumably occurs with torsional support wires.
Does anyone have any expert knowledge in this field to resolve the issue?
My colleague argues that provided the torsional support is not taken past its elastic limit it will have an essentially unlimited life. My argument is that even for small motions it will fail eventually due to fatigue or hysteresis. Obviously the support may eventually deteriorate due to decomposition of the support, but not withstanding that I would expect that after a few years of rocking backwards and forwards at a 50Hz rate it will break. I suspect that the support is some sort of rubber/plastic/elastomer but the same effect presumably occurs with torsional support wires.
Does anyone have any expert knowledge in this field to resolve the issue?





RE: Lifetime of a torsional support?
8cycles without breaking. Some interpret the available data (for steel) to indicate theoretically infinite fatigue life is possible, for the most part most fatigue testing is halted after 107to 108cycles for economic reasons. For other materials, the existence of a "knee" in the fatigue life vs. stress level plot is not as evident as it is for steel.At 50 Hz, operating 24/7, you'll get to 10
8cycles in about 23 days. I know of a lot of pieces of equipment that have survived cyclic motion for much longer than that.RE: Lifetime of a torsional support?
RE: Lifetime of a torsional support?
I know cam belts in cars break after 60,000 miles or so and I assumed that a similar failure mechanism would take place in a torsional vibration situation.
Thanks for the response. I have now googled on the idea of fatigue level vs stress plot and got some useful data.
It is surprising how a little push in the right direction can be such an asset. Thanks
RE: Lifetime of a torsional support?
TTFN
RE: Lifetime of a torsional support?