Analysis Of Vibration And Damage Test Of Ceramic Matrix Composites Structure

Advanced composites take full advantage of the feature of each component to give the entire structure excellent mechanical properties.In the past three decades,advanced composite materials have been widely used in the aviation field,and have evolved from the original non-bearing members to the secondary bearing members and even the main bearing members,such as horizontal stabilizers,rudders,vertical tails,and front body.With the generation of aircraft development,aero engines face the challenge of higher temperatures,higher pressures and higher speeds.Ceramic matrix composites are expected to be an alternative to new generation aerospace engine blades due to their low density,high temperature resistance,high specific strength and oxidation resistance.General Electric Company(GE)has completed critical testing of ceramic-based composite turbine rotor blades on the F414 modified engine.Benefits from the application of ceramic-based composite blades,the overall weight of the engine becomes lighter,and due to the high temperature resistance of the ceramic-based composite,the pre-turbine temperature can be increased to further improve engine fuel efficiency.However,due to the various manufacturing processes and complicated steps in the production process of ceramic matrix composite materials,some defects remain inside the materials.So how to judge the nature of internal defects of materials through effective detection means and effectively monitor the material during service has become a necessary issue.In this paper,based on the ceramic matrix composite structure,a variety of natural frequency measurement methods and damage detection methods are used to study the law between the natural frequency and the damage condition and the rotation speed change of the ceramic matrix composite rotating structure.Firstly,the overspeed rotor experiment was carried out on the prepared ceramic matrix composite structure by using the overspeed rotor test bench to simulate the working environment and determine the critical dangerous speed of the sample overspeed rotor experiment.Secondly,a set of high-precision natural frequency measurement methods and devices are designed.It has been verified that this measurement method can effectively eliminate the measurement error caused by the fixture's changes to the boundary conditions of the structure.Adopting wheel disc fixing,"hammer-sound pressure sensor" measuring;wheel disc fixing,"piezoelectric ceramic-laser vibrometer" measuring and fixture fixing "piezoelectric ceramic-laser vibrometer" measuring various natural frequency measurement methods to variable control analysis the ceramic matrix composite structure.In addition,micro-CT scanning and "weak magnetic method" were used to detect the damage of ceramic matrix composites.The development of structural cracks and the distribution characteristics of cracks were analyzed.It is proved that the damage location formula is also applicable to the damage location of ceramic matrix composite structures.Finally,the damage of ceramic matrix composites was determined according to the yield strength of ceramic matrix composites and the dangerous critical speed of the structure.The empirical formula of damage determination was given based on the natural frequency variation.