Simulation of the Crack Geometry Effect on the Natural Vibration Frequency of a Plate Blade

Free and fixed plate blade root states were simulated with finite element analysis to reveal the crack effect on the natural vibration frequency of the blade. Natural vibration frequencies are obtained for blades with different crack locations and lengths. The crack is found to reduce the blade stiffness and to affect its natural vibration frequency. The longer the crack, the greater the change of the stiffness, and the more the natural vibration frequency decreases. In the free state, the effect of the cracks of the same length on the natural vibration frequency is basically identical when it lies between the two nodal lines of first-order bending vibrations. The crack effect at a height of one-half the blade in the free state on natural frequencies is very close to that of the cracks of the same length at a height of one-eighth the blade in the fixed state. Practical guidelines for the detection of fracture cracks are given and the crack length and location were evaluated by frequency variations.