What are the most critical parameters in high-speed machines: stress or strain?

[zoltrix]

hello
consider an high speed machine
the inertial forces exceed the static ones
of course duttile materials
generally speaking which ones are the most critical parameters ?
stresses (von Mises etc) or strains ?

 

[jrmichler]

It is situation specific. The most critical parameter(s) could be one or more of:

Inertial forces (machines with reciprocating parts)
Natural frequency / critical speed (high speed shafts)
Stress
Strain
Friction heating (Ask me about the time we put 8 ball bearings in a volume the size of a basketball that generated 2 kW of heat)
Aerodynamic forces (Napkin folders at 12,000 napkins per minute)
Deflection (Can be too large at low strain)
Flame speed (Internal combustion engine)

And more, but that's the first ones off the top of my head. And all of the above are based on my personal experience with high speed machines.

 

[berkeman]

Friction heating (Ask me about the time we put 8 ball bearings in a volume the size of a basketball that generated 2 kW of heat)

 

[zoltrix]

I suppose that for high speed machines deformations are , generally speaking, a more serious issue than stresses
just to make it simple, take an hinged-hinged square linkage subjected to an inertial transversal load concentrated in the center of mass
max deflection is proportional to length^3 while max stress to length
of course other parametrs might be even more important, it is so obvious that IMHO there was no need to mention them

 

[jack action]

I suppose that for high speed machines deformations are , generally speaking, a more serious issue than stresses

This is assuming the position is important. It may be totally irrelevant for the machine to do its job properly. Deformation might even be a desired feature.

 

[Chestermiller]

Usually, strength and yield behavior is quantified in terms of the principal stresses.