Evaluation of Resonant Conditions Causing High Cycle Fatigu in Bladed-disk Assemblies of Turbomachines Using Modal Analysis

Modal testing of bladed-disk assemblies is used to Identify the critical natural frequencies and mode shapes for avoiding the resonant conditions that cause high cycle fatigue (HCF) leading to premature blade and disk failures. In order to obtain the high-quality modal data necessary for accurate modal identification, experience plays a major role In understanding the strengths and weaknesses associated with the variety of testing techniques. Choices such as pre-test bladed-disk preparation, modal excitation driving point location, hammer versus shaker force excitation methods, shaker driving signal approaches, accelerometer type and location, and windowing are all important aspects that must be considered when testing specific bladed-disk configurations. Modal analysis techniques Including extraction of harmonic content and use of interference diagrams for identification of resonance conditions are presented.