Force Limited Vibration Using the Apparent Mass Method

Force Limited Vibration is a technique that reduces the severity of over-tests during vibration testing by limiting the acceleration input based on the maximum expected in-service interface force. In this paper, the sources of over testing are reviewed and a new method called the Apparent Mass method for deriving the maximum in-service interface force is presented. In this method, the maximum in-service interface force over a given bandwidth is predicted using the full three dimensional linear-elastic theory supplemented by the necessary conditions for a representative vibration test, the assumption that the test article and its in-service mounting structure are lightly damped, and that the in-service forces exciting the mounting structure are broadband. The resulting equation is shown by numerical example to produce significant notching without producing an under-test situation, even for extremely light test articles.