The Use of Random Vibration Methods for Dynamic Loading of a Structural Link

The application of random vibration methods is usually limited to the inertial loading of components, with a test being controlled by an accelerometer on an electrodynamic shaker. However it is possible to apply the same philosophy to dynamic load testing, where the electrodynamic shaker is controlled from a load cell. The test input is defined by a Power Spectral Density plot in terms of load rather than acceleration.

A situation was encountered with a structural link in which loosening occurred when it was subjected a real-world dynamic environment. It was desired to simulate this situation in the laboratory so that other configurations of the link could be evaluated for elimination of the phenomenon. Since the real world environment is random in nature it was desirable to utilize a loading input which simulated this. Real world load data was unavailable for developing the test so a generic input spectrum was used and converted to terms of loads. Preliminary laboratory testing indicated that the phenomenon was aggravated by frequencies greater than the range of available hydraulic apparatus so an electrodynamic shaker was employed. For the resultant test, one end of the link was mounted to a rigid fixture, the other end was attached to the armature of the shaker, and a random loading spectrum was applied.