Measurement of Air Layer Thickness under Multi-Angle Incidence Conditions Based on Ultrasonic Resonance Reflection Theory for Flange Fasteners

Abstract

During the servicing of flange fasteners, the sealing gasket and the flange cover interface are prone to separation and air contamination due to factors such as stress, corrosion, and vibration. In the detection process, there are two main issues: firstly, the conventional ultrasonic measurement methods based on the theory of acoustic elasticity are not applicable due to the small thickness of the air layer; secondly, the use of conventional vertical incidence detection methods is difficult to ensure due to the influence of the actual structure. To address these issues, this paper first establishes a mathematical model of ultrasonic resonance reflection, and then calculates the corresponding relationship between the air layer thickness and the resonance frequency under vertical incidence conditions. However, this model is difficult to use to calculate the resonance frequency under different incidence angles. To meet the requirements of different working conditions, a finite element simulation model is further established. By comparing the calculation results of the two models under vertical incidence, the reliability of the established finite element model is verified. The reflection and transmission pressure acoustic field distribution under different incidence angles and air layer thicknesses is simulated, and the function relationship between the incidence angle, air layer thickness, and the corresponding first-order resonance frequency is derived. This enables the measurement of the air layer thickness at any incidence angle, providing technical and theoretical support for practical industrial applications.