Design of acoustic Fresnel zone plate for contact stress measurement of aero-engine rotor mating surface

Abstract

• PR-FZP made of non-metallic materials with the acoustic impedance closer to that of water all have a strong focusing ability. • Adding matching layers can improve the focus gain of PR-FZP to a certain extent. • Adding a reflecting layer can significantly improve the focus gain of PR-FZP. Accurate measurement of the contact stress on the mating surface of the core engine's multi-stage rotor is of great significance for improving the structural connection quality and comprehensive performance of aero-engines. The phase reversal Fresnel zone plate (PR-FZP) can realize the focusing of ultrasonic wave and its focusing ability has an important influence on the measurement accuracy of contact stress based on ultrasonic method. To improve the focusing ability of PR-FZP, this paper compares the focusing effect of PR-FZP made of different materials and designs PR-FZP with different structures based on the in-depth analysis of the focusing principle of PR-FZP. Numerical simulation results show that among the six selected materials, the single material PR-FZP made of polymethyl pentene (PMP) is always the highest with the change of working conditions. For PR-FZP with matching layer structure (M-PR-FZP), the focus gain is 0.21 dB higher than that of PR-FZP made of a single material. The focus gain of PR-FZP with reflecting layer structure (R-PR-FZP) can reach 24.84 dB, which is 6.01 dB and 1.45 dB higher than that of single metal (brass) Soret Fresnel zone plate (Soret FZP) and single non-metallic material (PMP) PR-FZP, respectively. This study has important guiding significance for improving the focusing ability of PR-FZP and realizing the accurate measurement of contact stress of aero-engine rotor mating surface.