EXPERIMENTAL-STUDY OF THE NATURAL FREQUENCIES OF ROTATING THIN-WALLEDCOMPOSITE BLADES

The paper presents an experimental method for detecting the natural fr equencies of helicopter-like thin-walled rotating composite blades, an d a study of their dependency in the lamination angles and in the roto r angular velocity. The tests were carried out in a vacuum chamber whi ch allowed the isolation of the structural dynamic effects. Both symme tric and antisymmetric box-beam specimens were tested. The blades were excited by an impulse force during rotation and the time history of t he resulting strain distributions were recorded. Natural frequencies h ave been obtained by numerical analysis of the time response. The resu lts demonstrate high repeatability and clear trends of the natural fre quencies variation as a function of the blade lamination modes and the ir angular velocity.