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Railroad Car Vibration Testing

Railroad Car Vibration Testing

Railroad Car Vibration Testing

(OP)
I have been given Acceptance Criteria for vibration testing of a railroad car, steady-state, that I am not sure how to interpret:

For the frequency range from 1 to 14 Hz, vibration values cannot exceed:
0.10 inch pk-pk displacement amplitude,
0.01 g pk acceleration,
0.045 inch per second vibration velocity

At first I thought to do an FFT analysis of the vibration signal from 1 - 14 Hz and pick the highest amplitude as my value. Then I reconsidered and thought to analyze the whole time-domain signal through a low-pass filter at 14 Hz and take the highest amplitude as my value.

Does anyone know how I could find the original spec for this type of testing? What are your interpretations of this requirement?

Thanks,
Chad Schneider

RE: Railroad Car Vibration Testing

My impression is that it is a swept sine test, so you only need to work with one frequency at once. The three criteria can all be transformed into an acceleration limit, by appropriate differentiation .

This will give you three curves on the acceleration spectrum. Incidentally the velocity measurement is not fully specified - is that pk, pk-pk, or rms?

I get:

Acceleration limit =3.86 in/s/s pk

velocity limit=.045 in/s (assume pk)=2*pi*f*.045 in/s/s pk

displacement limit=.1 in pk-pk = .05 in pk=(2*pi*f)^2*.05 in/s/s pk


Then if your response exceeds any of those limits, you've failed.

If it is not a swept sine test, then you would have to bandpass the acceleration signal, and then integrate it and compare it with each limit, in the time domain. This doesn't sound very likely.

Cheers

Greg Locock

RE: Railroad Car Vibration Testing

The most common acceptance criteria for railroad vehicles ( lcomotive, pass. coach and wagons)are UIC 518 and UIC 516 which are followed in Europe. The Americans follow the AAR standards which is covered in chapter 10 of the standard (this is applicable for wagons only).
Normally accelerations and displacements in vertical and lateral mode are measured by analog method on a recorder. the peak to peak values  for accelerations should comform the limits given to you by the customer, these values are measured are the vehicle floor lever just above the pivot location. For the displacments the spring deflections of primary and secondary springs are measured.

RE: Railroad Car Vibration Testing

Something's not adding up.  I expected the displacement and acceleration to match at the beginning of the sweep (1Hz) and velocity and acceleration to match at the end of the sweep (14Hz).

At 1Hz, 0.1 in pk-pk is equal to 0.01 G pk-pk (not G pk) and, at 14Hz, 0.45 ips pk equals 0.01 G pk (as listed).

Regards .. kv

RE: Railroad Car Vibration Testing

Those are just acceptance criteria you've been given, each independent of the other.  That is, neither the velocity, displacement, nor acceleration limits can be exceeded anywhere within the 0 - 14 Hz frequency range.  Presumably, under any operating condition.
Note that, Greg's comments notwithstanding,  the usual units for measurement of velocity (when not expressed otherwise)are 0 - peak, not peak-peak nor RMS.
Like on the speedometer in your car.

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