The study on algorithm for identification the fatigue crack length of compressor blade based on amplitude-frequency resonant characteristics

The article is focused on building the algorithm for identification the fatigue crack length in the first stage of compressor blade of the helicopter PZL-10W turbo-shaft engine. The fatigue wear of compressor blade is a process in which the fatigue crack begins at the structural notch of the working part. For compressor blade, the crack starts at the leading edge and progress along the blade chord. Due to working conditions, the compressor blades are referred to as critical components. The helicopter rotor downwash can easily lift particles form the ground that may cause damages in the compressor section. Aircraft engines are designed so that the rotational speed of impeller remains below the resonant frequency. However, the pulsation of working medium or mechanical vibrations may cause temporary increase of vibration frequency. The appearance of structural notch combined with temporary increase of vibrations may initiate the fatigue failure. The works undertaken at the Department of Aircraft and Aircraft Engines, Rzeszow University of Technology provided a wide spectrum of research data of amplitude-frequency (A-F) characteristics of 1st stage of compressor blade. For different crack lengths, the fatigue tests of resonant frequency and asymmetry of A-F characteristics were acquired. The crack lengths were measured by fluorescent or infrared mapping method. The aim of the article is to develop the numerical method for identification of crack length of compressor blade basing on A-F characteristics. The studies on A-F characteristics in order to find correlations between crack length, resonant frequency and characteristics asymmetry were performed. The next step was to build the algorithm for identification the crack length when only A-F characteristic is known. The article contains the description of researches background, A-F characteristics unique features, algorithm detailed methods of work and sample use of algorithm in identification the crack length.