Limitations of the Power Spectral Density as an Indicator of Test Severity

Abstract

This paper presents a set of experimental data comparing repetitive shock (RS) vibration, single-axis electrodynamic (ED) vibration, and multi-axis ED vibration. It was found that multi-axis testing is more severe than single-axis testing at the same level. In addition, weaknesses were found in the RS system at low frequency. Smoothing of the data or poor line resolution was also shown to change the overall severity of a test. A poor correlation was shown between the power spectral density (PSD) and the rate of natural frequency change (RFC) over a wide frequency shift. The change in natural frequency caused the initial PSD to be an ineffective indicator of test severity. Quantification of the severity of the test profile can be accomplished through characterization of the RFC.