The document provides an introduction to vibration qualification testing, discussing its importance and the various sources and types of vibrations, including sinusoidal and random vibrations. It explains how vibrations are analyzed and replicated in a lab setting using different types of shakers, such as electrodynamic and hydraulic shakers. The presentation aims to enhance understanding of vibration's impact on engineering and reliability 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