Response and Durability of Large Radius of Gyration Structures Subjected to Biaxial Vibration

Multiaxial vibration tests were conducted using an electrodynamic shaker capable of controlled vibration in six degrees of freedom. The test specimen consisted of six large inductors insertion mounted on a printed wiring board. Average damage accumulation rate was measured for random excitation in-plane, out-of-plane, and both directions simultaneously. Under simultaneous biaxial excitation, the damage rate was found to be 2.2 times larger than the sum of the in-plane and out-of-plane rates. The conclusion was that multiple-step single-degree-of-freedom testing can significantly overestimate the durability of some structures in a multiaxial environment. To examine the mechanics behind this phenomenon, the response of a simple rod structure was analyzed with the finite element method. Axial vibrations, which produce negligible stress on their own, were found to contribute significant additional stress when combined with transverse vibration. This additional stress contribution was found to be highly dependent on the frequency ratio and phase relationship between the two participating axes