Simultaneous Qualification Testing of Multiple Components and the Influence of Closely Spaced Vibration Modes

Abstract

Vibration and shock qualification testing of components can be an expensive and time-consuming process. If the component is small, often two or more units can be mounted on a fixture and tested simultaneously to reduce test time. There is an inherent danger in simultaneously testing two or more identical components as the fundamental natural frequencies and mode shapes of the individual components will be nearly identical with some slight variation due to manufacturing variability. Testing in this manner can create a situation where closely spaced vibration modes produce unwanted interference between the two units under test. This phenomenon could result in a case where one unit is over-tested while the other is under-tested. This paper presents some experimental results from simultaneously testing pairs of components which show distinct interference between the units. Some analysis will also be presented showing how variations in the components can alter the intended test response, potentially impacting component qualification.