Introduction to Vibration Qualification Testing

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

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Introduction to Vibration Qualification Testing

  1. 1. Introduction toVibrationQualificationTestingDavid Common©2013 ASQ & Presentation Commonhttp://reliabilitycalendar.org/webinars/
  2. 2. ASQ Reliability DivisionEnglish Webinar SeriesOne of the monthly webinarson topics of interest toreliability engineers.To view recorded webinar (available to ASQ ReliabilityDivision members only) visit asq.org/reliabilityTo sign up for the free and available to anyone livewebinars visit reliabilitycalendar.org and select EnglishWebinars to find links to register for upcoming eventshttp://reliabilitycalendar.org/webinars/
  3. 3. Engineering, Testing, Consulting andInspection ServicesDavid CommonDynamics Testing ManagerApplied Technical Services, Inc.Marietta, GAdcommon@atslab.com(678) 444-2905May 09, 2013Introduction to Vibration Qualification Testing
  4. 4. Agenda• Why should we care about vibrations ?• Where do vibrations come from ?• What are the types of vibration and how are theyanalyzed from a test lab perspective ?• How are vibrations replicated in the lab ?• In Practice• Questions?
  5. 5. Why should we care about vibrations ?Although some specific applications aim at creating‘good’ vibrations (loudspeakers), most vibrationsources have the potential to create issues.
  6. 6. Why should we care about vibrations ?(cont.)Issues can be of different kinds:• Functional (CD skip)• Comfort (squeak, rattle)• Structural
  7. 7. Where do vibrations come from ?• Machinery• Road
  8. 8. Where do vibrations come from ?• Wind load (Tacoma bridge)• Ground motion
  9. 9. What are the different types of vibrations?• Sinusoidal vibration• Most basic• Simple motion• One (1) frequency present at any given time
  10. 10. Sinusoidal Vibration0 10 20 30 40 50 60-1.5-1.0-0.500.51.01.5Time (ms)Acceleration(G)Acceleration WaveformCh110 1000.43.01.0Frequency (Hz)Acceleration(Gpeak)Acceleration ProfileDemandControl
  11. 11. Sinusoidal Vibration0 5 10 15 20 25 30-0.8-0.6-0.4-0.200.20.40.60.8Time (sec)Acceleration(G) AccelerationDemandCh1
  12. 12. Sinusoidal Vibration
  13. 13. Sinusoidal Vibration - Quantification• Typically expressed as:• Acceleration vs. frequency• Velocity vs. frequency• Displacement vs. frequency• Any combination of the above vs. frequency
  14. 14. • Random vibration• ‘Random’ nature due to incapacity to predictprecise vibration level at any given time• Quantified using statistical tools• Broadband, multi-frequency content• More closely match real-world excitationsWhat are the different types of vibrations?
  15. 15. Random Vibration10 100 1000-61x10-51x10-41x10-31x10Frequency (Hz)AccelerationSpectralDensity(G²/Hz)Acceleration Spectral DensityDemandCh10 500 1000 1500 2000 2500 3000 3500 4000-6-4-20246Time (ms)Acceleration(G)Acceleration WaveformCh1
  16. 16. Random Vibration – Really random?10 100 1000-61x10Frequency(Hz)AcDemandCh10 500 1000 1500 2000 2500 3000 3500 4000-6-4-20246Time(ms)Acceleration(G)AccelerationWaveformCh1
  17. 17. Random Vibration – Kurtosis adjustment50 100-26x10-11x10Frequency(Hz)AcceleratiCh10 500 1000 1500 2000 2500 3000 3500 4000 4500 5000-60-40-200204060Time(ms)Acceleration(G)AccelerationWaveformCh1
  18. 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 tothe bandwidth of analysis (since dealing with a broadbandexcitation)• Tabulated values will sometimes have a ‘gRMS’ value added:• This is the overall energy introduced by the randomvibration profile (integrates PSD vs. frequency)
  19. 19. Random Vibration – Different shapes…2001 10 100-51x10-41x10-31x10-21x10Frequency (Hz)AccelerationSpectralDensity(G²/Hz)Acceleration Spectral DensityCh10 500 1000 1500 2000 2500 3000 3500 4000 4500 5000-3-2-10123Time (ms)Acceleration(G)Acceleration WaveformCh1• Truck transportation simulation
  20. 20. Random Vibration – Different shapes…• Engine compartment simulation60 100 1000-61x10-51x10-41x10-31x10-21x10Frequency (Hz)AccelerationSpectralDensity(G²/Hz)Acceleration Spectral DensityCh10 100 200 300 400 500 600 700-6-4-20246Time (ms)Acceleration(G)Acceleration WaveformCh1
  21. 21. Let’s mix things up – Sine on Random• Add discreet sinusoidal vibration tones to a broadbandrandom vibration background• Typical of helicopter and propeller aircraft applications(known blade passing frequencies on a randombackground)
  22. 22. Let’s mix things up – Sine on Random20 2000100 1000-41x10-31x10-21x10-11x1001x10Frequency (Hz)AccelerationSpectralDensity(G²/Hz)Acceleration Spectral DensityCh10 500 1000 1500 2000 2500 3000-10-50510Time (ms)Acceleration(G)Acceleration WaveformCh1
  23. 23. Let’s mix things up – Random on Random• Add narrowband random content onto a broadbandrandom background• Typical of tracked vehicles (military)• Narrowband content is swept across a frequency rangeto reflect speed changes
  24. 24. Let’s mix things up – Random on Random20 2000100 1000-41x10-31x10-21x10-11x1001x10Frequency (Hz)AccelerationSpectralDensity(G²/Hz)Acceleration Spectral DensityDemandCh10 500 1000 1500 2000 2500 3000 3500 4000-20-15-10-505101520Time (ms)Acceleration(G)Acceleration WaveformCh1
  25. 25. Random vibration vs. Transients…• Traditional random vibration averages out the actualvibration history.• Transients such as bumps, potholes, etc. do not translatewell into random• Another technique is needed to replicate transients
  26. 26. • Field data replication• Data collected in the field (acceleration vs. time)is directly played back and repeated in the labWhat are the different types of vibrations?
  27. 27. Field data replication0 10000 20000 30000 40000 50000 60000-2-10123Time (ms)Acceleration(G)AccelerationDemand0 10000 20000 30000 40000 50000 60000-2-101234Time (ms)Displacement(in)DisplacementDemand0 10000 20000 30000 40000 50000 60000-20-10010203040Time (ms)Velocity(in/s)VelocityDemand
  28. 28. How are vibrations replicated in the lab?• Shakers• Mechanical• Electrodynamic• Hydraulic• Single/Multi-axis
  29. 29. How are vibrations replicated in the lab?• Mechanical shakers (‘direct drive’)• 1950’s• Cheap, sinusoidal excitation• Still used today for shipping vibration testCourtesy of Lansmont Corporation
  30. 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 eachother
  31. 31. Electrodynamic shakers
  32. 32. Electrodynamic shakers – Combined• Shakers can becombined with thermalchambers (‘AGREE’chambers) fortemperature andvibration testing(engine-mountedcomponents might seehigh vibration levelsand extremetemperature range)
  33. 33. Electrodynamic shakers• Medium to high frequency range (typically from5Hz to 2,000Hz)• Low available displacement (2” peak-to-peak)
  34. 34. Electrodynamic shakers• Fun with astrobelight…
  35. 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. 36. Hydraulic shakers• Single-axisCourtesy of Dynamic Testing and Equipment
  37. 37. Hydraulic shakers (Triaxial)• Triaxial hydraulic shaker table
  38. 38. Hydraulic shakers – Triaxial
  39. 39. In Practice…• Fixtures…• Position of the control accelerometer…• How many control accels?• Sliptable use…
  40. 40. In Practice… Fixtures
  41. 41. In Practice… Fixtures
  42. 42. In Practice… SliptablesCourtesy of Unholtz-Dickie Corporation
  43. 43. In Practice… SliptablesCourtesy of Unholtz-Dickie Corporation
  44. 44. Multiple control accelerometers - Extremal• Two control accelerometers used in an ‘Extremal’strategy
  45. 45. Multiple control accelerometers - Average• Four control accelerometers used in an ‘Average’strategy
  46. 46. Multiple shakers• Testing of large/heavy payloadsCourtesy of Lansmont Corporation
  47. 47. Questions?• Contact info:• David Common – dcommon@atslab.com• (678) 444-2905

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