Few Common Observations From a Vibration Test Data

Typical vibration test data, especially from transient vibration tests, contains several observations with reference to test data measurement quality and physics of response. In this paper, few common observations are highlighted. These observations are obtained from both shock type test and steady state vibration test. First observation — In case of shock type loading, accelerometer data is usually found to have multiple local drifts in the signal. It is understood that presence of these multiple drifts doesn’t necessarily mean that the data is corrupted, but data can still be very reliable if drifts are removed. Second observation — In a system with significant rubs during dynamic test, it is commonly observed that vibration response contains frequencies of multiple orders of fundamental excitation frequency. Vibration at multiple orders is localized to the rubbing zone and dies away as we move far from the rubbing zone. Third observation — During shock testing, accelerometers contain large acceleration at higher frequencies, while strain gauge data doesn’t usually show significant strain at higher frequencies. Higher acceleration at higher frequencies leads to smaller displacement which then leads to lower loading into the system. Fourth observation — In case of base excitation tests, in which input signal is multi-tonal, high frequency tones gets attenuated through the compliant mounting and doesn’t show as an output on mounted device. These observations are described in detail in this paper.