CRITICAL SPEEDS AND BUCKLING LOADS OF A PRETWISTED ROTOR

The equations of motion of a pre-twisted rotor subjected to a compress ive axial load have been derived by including the effects of transvers e shear, rotatory inertia and gyroscopic moments to model material rem oval systems which have external flutes. The finite element method is used to obtain a system of ordinary differential equations. C-0-compat ible finite elements are used to obtain the critical speeds and buckli ng loads for different helix angles, flute lengths and drill diameters for various support conditions. The critical speeds decrease with inc reasing compressive axial load. The lowest mode is associated with a c ritical thrust force which corresponds to a zero critical speed. This critical thrust force is the buckling load of the lowest mode of the n onrotating pre-twisted rotor.