A free monthly webinar hosted by ASQ Reliability Division presenting David Common on Introduction to Vibration Qualification Testing

1. Introduction to
Vibration
Qualification
Testing
David Common
©2013 ASQ & Presentation Common
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3. Engineering, Testing, Consulting and
Inspection Services
David Common
Dynamics Testing Manager
Applied Technical Services, Inc.
Marietta, GA
dcommon@atslab.com
(678) 444-2905
May 09, 2013
Introduction to Vibration Qualification Testing

4. Agenda
• Why should we care about vibrations ?
• Where do vibrations come from ?
• What are the types of vibration and how are they
analyzed from a test lab perspective ?
• How are vibrations replicated in the lab ?
• In Practice
• Questions?

5. Why should we care about vibrations ?
Although some specific applications aim at creating
‘good’ vibrations (loudspeakers), most vibration
sources have the potential to create issues.

6. Why should we care about vibrations ?
(cont.)
Issues can be of different kinds:
• Functional (CD skip)
• Comfort (squeak, rattle)
• Structural

7. Where do vibrations come from ?
• Machinery
• Road

8. Where do vibrations come from ?
• Wind load (Tacoma bridge)
• Ground motion

9. What are the different types of vibrations?
• Sinusoidal vibration
• Most basic
• Simple motion
• One (1) frequency present at any given time

10. Sinusoidal Vibration
0 10 20 30 40 50 60
-1.5
-1.0
-0.5
0
0.5
1.0
1.5
Time (ms)
Acceleration(G)
Acceleration Waveform
Ch1
10 100
0.4
3.0
1.0
Frequency (Hz)
Acceleration(Gpeak)
Acceleration Profile
Demand
Control

11. Sinusoidal Vibration
0 5 10 15 20 25 30
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Time (sec)
Acceleration(G) Acceleration
Demand
Ch1

12. Sinusoidal Vibration

13. Sinusoidal Vibration - Quantification
• Typically expressed as:
• Acceleration vs. frequency
• Velocity vs. frequency
• Displacement vs. frequency
• Any combination of the above vs. frequency

14. • Random vibration
• ‘Random’ nature due to incapacity to predict
precise vibration level at any given time
• Quantified using statistical tools
• Broadband, multi-frequency content
• More closely match real-world excitations
What are the different types of vibrations?

15. Random Vibration
10 100 1000
-6
1x10
-5
1x10
-4
1x10
-3
1x10
Frequency (Hz)
AccelerationSpectralDensity(G²/Hz)
Acceleration Spectral Density
Demand
Ch1
0 500 1000 1500 2000 2500 3000 3500 4000
-6
-4
-2
0
2
4
6
Time (ms)
Acceleration(G)
Acceleration Waveform
Ch1

16. Random Vibration – Really random?
10 100 1000
-6
1x10
Frequency(Hz)
Ac
Demand
Ch1
0 500 1000 1500 2000 2500 3000 3500 4000
-6
-4
-2
0
2
4
6
Time(ms)
Acceleration(G)
AccelerationWaveform
Ch1

17. Random Vibration – Kurtosis adjustment50 100
-2
6x10
-1
1x10
Frequency(Hz)
Accelerati
Ch1
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
-60
-40
-20
0
20
40
60
Time(ms)
Acceleration(G)
AccelerationWaveform
Ch1

18. Random Vibration – Quantification
• Expressed as PSD (‘Power Spectral Density’) or ASD
(‘Acceleration Spectral Density’) vs. frequency
• Dimension is g2/Hz (or (m/s2)2xs)
• PSD is the random vibration level, normalized with respect to
the bandwidth of analysis (since dealing with a broadband
excitation)
• Tabulated values will sometimes have a ‘gRMS’ value added:
• This is the overall energy introduced by the random
vibration profile (integrates PSD vs. frequency)

19. Random Vibration – Different shapes…
2001 10 100
-5
1x10
-4
1x10
-3
1x10
-2
1x10
Frequency (Hz)
AccelerationSpectralDensity(G²/Hz)
Acceleration Spectral Density
Ch1
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
-3
-2
-1
0
1
2
3
Time (ms)
Acceleration(G)
Acceleration Waveform
Ch1
• Truck transportation simulation

20. Random Vibration – Different shapes…
• Engine compartment simulation
60 100 1000
-6
1x10
-5
1x10
-4
1x10
-3
1x10
-2
1x10
Frequency (Hz)
AccelerationSpectralDensity(G²/Hz)
Acceleration Spectral Density
Ch1
0 100 200 300 400 500 600 700
-6
-4
-2
0
2
4
6
Time (ms)
Acceleration(G)
Acceleration Waveform
Ch1

21. Let’s mix things up – Sine on Random
• Add discreet sinusoidal vibration tones to a broadband
random vibration background
• Typical of helicopter and propeller aircraft applications
(known blade passing frequencies on a random
background)

22. Let’s mix things up – Sine on Random
20 2000100 1000
-4
1x10
-3
1x10
-2
1x10
-1
1x10
0
1x10
Frequency (Hz)
AccelerationSpectralDensity(G²/Hz)
Acceleration Spectral Density
Ch1
0 500 1000 1500 2000 2500 3000
-10
-5
0
5
10
Time (ms)
Acceleration(G)
Acceleration Waveform
Ch1

23. Let’s mix things up – Random on Random
• Add narrowband random content onto a broadband
random background
• Typical of tracked vehicles (military)
• Narrowband content is swept across a frequency range
to reflect speed changes

24. Let’s mix things up – Random on Random
20 2000100 1000
-4
1x10
-3
1x10
-2
1x10
-1
1x10
0
1x10
Frequency (Hz)
AccelerationSpectralDensity(G²/Hz)
Acceleration Spectral Density
Demand
Ch1
0 500 1000 1500 2000 2500 3000 3500 4000
-20
-15
-10
-5
0
5
10
15
20
Time (ms)
Acceleration(G)
Acceleration Waveform
Ch1

25. Random vibration vs. Transients…
• Traditional random vibration averages out the actual
vibration history.
• Transients such as bumps, potholes, etc. do not translate
well into random
• Another technique is needed to replicate transients

26. • Field data replication
• Data collected in the field (acceleration vs. time)
is directly played back and repeated in the lab
What are the different types of vibrations?

27. Field data replication
0 10000 20000 30000 40000 50000 60000
-2
-1
0
1
2
3
Time (ms)
Acceleration(G)
Acceleration
Demand
0 10000 20000 30000 40000 50000 60000
-2
-1
0
1
2
3
4
Time (ms)
Displacement(in)
Displacement
Demand
0 10000 20000 30000 40000 50000 60000
-20
-10
0
10
20
30
40
Time (ms)
Velocity(in/s)
Velocity
Demand

28. How are vibrations replicated in the lab?
• Shakers
• Mechanical
• Electrodynamic
• Hydraulic
• Single/Multi-axis

29. How are vibrations replicated in the lab?
• Mechanical shakers (‘direct drive’)
• 1950’s
• Cheap, sinusoidal excitation
• Still used today for shipping vibration test
Courtesy of Lansmont Corporation

30. How are vibrations replicated in the lab?
• Electrodynamic shakers
• Make most of the fleet of commercial test labs
• Sequential, single-axis excitation
• Big, highly-controlled ‘loudspeakers’
• Come in various sizes and shapes (sliptable)
• Rated in lbf
• Payload and severity counterbalance each
other

31. Electrodynamic shakers

32. Electrodynamic shakers – Combined
• Shakers can be
combined with thermal
chambers (‘AGREE’
chambers) for
temperature and
vibration testing
(engine-mounted
components might see
high vibration levels
and extreme
temperature range)

33. Electrodynamic shakers
• Medium to high frequency range (typically from
5Hz to 2,000Hz)
• Low available displacement (2” peak-to-peak)

34. Electrodynamic shakers
• Fun with a
strobe
light…

35. Hydraulic shakers
• Low frequency range (typically 1Hz to 100Hz)
• High available displacement (10” or 12” peak-to-
peak)
• Often offer the highest force rating for the buck

36. Hydraulic shakers
• Single-axis
Courtesy of Dynamic Testing and Equipment

37. Hydraulic shakers (Triaxial)
• Triaxial hydraulic shaker table

38. Hydraulic shakers – Triaxial

39. In Practice…
• Fixtures…
• Position of the control accelerometer…
• How many control accels?
• Sliptable use…

40. In Practice… Fixtures

41. In Practice… Fixtures

42. In Practice… Sliptables
Courtesy of Unholtz-Dickie Corporation

43. In Practice… Sliptables
Courtesy of Unholtz-Dickie Corporation

44. Multiple control accelerometers - Extremal
• Two control accelerometers used in an ‘Extremal’
strategy

45. Multiple control accelerometers - Average
• Four control accelerometers used in an ‘Average’
strategy

46. Multiple shakers
• Testing of large/heavy payloads
Courtesy of Lansmont Corporation

47. Questions?
• Contact info:
• David Common – dcommon@atslab.com
• (678) 444-2905