Analysis and experimental verification of dynamic characteristics of cantilever plate with fatigue crack

Abstract

Fatigue cracks in aero-engine blades seriously threaten the stability and reliability of the engine. It is very necessary to identify and diagnose the crack state through vibration signals, and predicting its vibration rules through dynamic analysis is the basis of crack identification. At present, the dynamic model of cracked blades with breathing cracks is mainly established by implanting cracks, and there is a lack of relevant experimental validation. To address the above deficiencies, this paper firstly obtains the real extension path of the cracked plate through the fatigue testing machine, and then introduces it into the cantilever plate finite element model. Then the correctness of the proposed model is verified by natural frequency obtained from hammering test and frequency sweeping test. Finally, the effect of different crack parameters such as crack depth, crack location and plate length on the crack vibration characteristics is investigated based on simulations and experiments. The results indicate that (1) the real fatigue crack obtained by tensile test has larger amplitude peaks under excitation frequency compared with wire-cut crack, and it has stronger nonlinearity to better reflect the vibration characteristics; (2) Specimens show obvious nonlinear characteristics that significant amplitude peaks occur at multiples of excitation frequencies in both experiments and simulations; (3) For the cantilever plate containing breathing cracks, the vibration amplitude totally increased by 18.5% with the increase of crack depth, and it decreased by 41.5% throughout as the crack location became further away from the plate root. This study provides a theoretical basis for detection and diagnosis of blade cracks.