Evaluation of a vibration text fixture

Abstract

Mechanical vibration tests require the use of vibrators, power amplifiers, accelerometers, and closed loop control systems. A device is needed to connect physically the specimen to be tested to the vibrator table referred to as vibration test fixture. To verify and validate a fixture to be used, an evaluation of its dynamical behaviour is mandatory. The fixture natural frequencies must be higher than the maximum test frequency. In this work, some issues about electrodynamic vibrators and fixtures are revised and the behaviour of a real fixture is analysed numerically and experimentally. The fixture natural frequencies and its response to a harmonic acceleration applied on its bottom surface are evaluated by using the finite element method. A real test was performed by applying slow swept sine acceleration to the fixture mounted in an electrodynamic vibrator and measuring its response. The effect of the closed loop control system on the fixture response is evaluated. It is shown that the control system plays an important role in the definition of the fixture useful operating frequency range.