Abstract
The purpose of this paper is to give a general explanation of the vibration phenomena encountered in turbine design. Detailed methods have been omitted. The behavior of a vibrating cantilever is expressed in terms of the exciting force and damping factor. The sources of damping and excitation are discussed. Impulse excitation is briefly considered and the reasons for its devastating effects are shown. The procedure of tuning low-pressure blading, to avoid resonance at the lower harmonics of the turbine speed, is explained in considerable detail. An apparatus for determining the natural frequency of blading, and another for applying both tensile and alternating bending stresses simultaneously, are described. The direct tensile stress in the test is plotted versus the alternating bending stress which causes failure, thus obtaining a curve which shows the resistance of the blade to any combination of these stresses. The designed stresses for certain turbine blades and the stresses involved in several blade failures have been plotted on this diagram for purposes of comparison.
