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

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SUMMARY

The discussion centers on critical parameters in high-speed machines, emphasizing that both stress and strain are significant, but strain often poses a greater concern. Key factors identified include inertial forces, natural frequency, stress, strain, friction heating, aerodynamic forces, and deflection. The conversation highlights that deformation is generally more critical than stress in high-speed applications, particularly when considering the effects of inertial loads on machine components. The importance of these parameters is context-dependent, with specific applications influencing their relevance.

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  • Understanding of inertial forces in mechanical systems
  • Knowledge of natural frequency and critical speed concepts
  • Familiarity with stress and strain analysis in materials
  • Awareness of friction heating effects in high-speed machinery
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  • Research the impact of inertial forces on machine design
  • Explore methods for calculating natural frequency in rotating systems
  • Study advanced stress and strain analysis techniques
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Mechanical engineers, machine designers, and anyone involved in the optimization and analysis of high-speed machinery will benefit from this discussion.

zoltrix
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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 ?
 
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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.
 
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jrmichler said:
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)
:oops:
 
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
 
zoltrix said:
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.
 
Usually, strength and yield behavior is quantified in terms of the principal stresses.
 

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