NATURAL FREQUENCIES OF CANTILEVER BLADES WITH RESILIENT ROOTS

It is difficult to enforce infinite rigidity at the root of a cantilever during vibration tests. The 'cantilever' frequencies measured from a single response curve are the resonant frequencies of the entire system, including the effects of indeterminate root conditions. In some structural systems, such as bladed disk assemblies, system resonances may occur in a cluster near a blade cantilever frequency, so that it is difficult to distinguish between assembly modes and the blade cantilever frequency. It is shown that in such cases, a more accurate determination of actual cantilever frequencies may be made by computing the ratio of tip and root displacements as a function of excitation frequency.