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Problems with Using Kurtosis in Random Vibration Testing

shaker

Free Webinar  - "Problems with Using Kurtosis in Random Vibration Testing"

Starting from fundamental vibration and fatigue damage concepts, kurtosis control on an electrodynamic shaker is found to be an inefficient, poorly defined, and non-portable method for delivering and describing fatigue damage. This webinar is a must-attend for anyone who specifies, administers, or performs vibration testing with kurtosis.

Watch the recording of the webinar now!

Overview:

Kurtosis control is widely touted as a way to increase the damage content of a random vibration test without changing the Power Spectral Density (PSD). However, when a peak stress definition of over-testing is constructed based on the standard linear material model, it is found that the most rapid vehicle for delivering damage without over-testing is never a test with increased kurtosis.

This presentation explains why adding kurtosis to a vibration specification instead of increasing the PSD automatically adds time, and therefore cost, to the test procedure. Further, it explains how different vendors might comply with the same kurtosis specification while delivering different amounts of fatigue damage and peak stress levels to the device under test.

In effect, vendors using different controllers will perform different tests. This is not because one controller is right and the other is wrong; the underlying kurtosis specification is inherently imprecise with regard to fatigue damage.

Key Take-Aways

  • Learn why the proper metric of over-testing is peak stress in resonance, not Power Spectral Density (PSD)
  • Understand that properly controlled random vibration tests employing kurtosis can always be replaced exactly by a schedule of Gaussian (i.e. "non-kurtotic") levels
  • Discover why increasing kurtosis is a quick, but non-unique, way to model variable vibration power
  • Understand why kurtosis will not reliably ensure that the desired amount of fatigue damage is delivered during testing