EXPERIMENTAL VERIFICATION OF DYNAMIC STABILITY OF VERTICAL CANTILEVERED COLUMNS SUBJECTED TO A SUB-TANGENTIAL FORCE

The intended aim of the paper is to give the experimental verification of the effect of non-conservative/follower force on the vibration and stability of cantilevered columns. In place of an ideal tangential force, a sub-tangential force produced by a real solid rocket motor is considered in this paper. A solid rocket motor is mounted to a vertical cantilevered column at its tip end. Rocket thrust of the motor produces a tangential/non-conservative force, while the self-weight of the motor a vertical/conservative force. Thus, the combined action of the rocket thrust and the self-weight of the rocket motor produces a sub-tangential force. It is assumed that a solid rocket motor is a rigid body. Therefore, a concentrated mass, a rotary inertia and a size of the rocket motor must be taken into account in vibration and stability analysis. FEM formulation of the vibration problem under consideration is conducted to depict the dynamic stability in the total applied force and the non-conservativeness parameter plane. Experiments were conducted to demonstrate the stabilizing effect of follower forces on the dynamics of vertical columns initially subjected to a conservative force due to the rocket motorʹs weight. It was assumed that the thrust and the self-weight were constant during the burning time of 4 s. The average thrust was 40 kgf (392 N), while the average dead weight of the motor was 14·2 kgf (139 N). Four test runs were made for sub-critical and critical column initially subjected to the dead weight of the motor. It was observed that the buckled column under the dead weight of the motor could be stabilized dynamically by applying the rocket thrust of 40 kgf, when a resultant compressive force of 54·2 kgf (531 N) was applied to the column.