An Experimental Approach for Structural Dynamic Modification of Fixture in Vibration Test Control

In environmental vibration test, the fixture is inserted between the shaker and the test specimen. It is desirable that the test specimen is excited with uniform force through the mounting points connected to the fixture. The flexural vibration of the fixture sometimes makes it impossible to excite the specimen uniformly. The deviations of the transmitted force cause the under-test, especially at anti-resonance frequencies, in vibration test control. In this paper, the method of experimental structural dynamic modification using transfer function synthesis method is applied to the design of vibration test fixture. The responses at any points on the fixture can be predicted utilizing the experimental data. Structural dynamic modification of fixture is performed so that the spectra at the mounting points may meet the specified reference spectrum. The values of the added masses, which will be attached on the fixture, are used as design variables for removing the under-tests in environmental vibration test. From the experimental results of vibration test control applied to the modified fixture and unmodified fixture, this method is shown to be an effective one.