Acceleration
amplitude is the trickiest to understand. To begin with, you must understand
that due to the nature of sinusoidal motion (the back and forth action),
the velocity is constantly changing. It goes from zero to a peak back to
0 back to the peak and so on. To change the velocity of something, acceleration
must be applied. To speed your car up, you apply the accelerator. To slow
your car down, you apply the brake.
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Acceleration measures
the rate of change of velocity.
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Velocity is changed
when a PUSHING or STRIKING action is applied.
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Pushing or striking
something is applying a 'force' and acceleration is, of course, force.
So why is acceleration
used in the high frequency range ?
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The rate of change
in velocity (acceleration) is more affected by frequency - how often something
is changing direction - than displacement - how far it is moving.
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Components moving
at high frequencies will never fail due to stress (displacement)
because the displacement amplitude is very small.
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Although there
are frequencies where velocity and acceleration overlap in their sensitivity
to failures, the higher the frequency involved (especially above about
120,000 cpm), the less likely a fatigue failure is and the more likely
it is that the forces being applied that are causing the movement will
be responsible for any failure that might occur.
-
Acceleration is
sensitive to the likelihood of a FORCE
related failure. In other words, a failure
due to the pushing and/or striking action the component is being subjected
to.
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