The Simulation Method for Ultrasonic Non-Destructive Testing of Delamination Defects in CMC Based on Air-Coupled Lamb Waves

Ceramic Matrix Composite (CMC) are widely used in aerospace due to the advantages such as high-temperature resistance and lightweight properties. Detecting defects within these materials is crucial for ensuring the safety of corresponding structures. In this paper, a finite element model of CMC model for layered structures is established for the ultrasonic non-destructive testing. Based on the computed tomography (CT) scan images and porosity of the material, a randomly distributed pore model is constructed to investigate the effect of pores on the ultrasonic signals. Random pores are also introduced in the simulation to ensure that the model corresponds as closely as possible to reality. Moreover, the feasibility of utilizing air-coupled ultrasonic excitation to generate specific frequency Lamb waves is verified. The effect of pore presence on the signal propagation is analyzed, and the effects of layered structures at different positions and lengths on the signal propagation are investigated. The results demonstrate that the Lamb waves with a specified frequency can be excited using the method described in this paper, and the presence of pores and delamination defects can affect the propagation of the Lamb wave in CMC, in which the signal attenuation can reach up to 7.6 dB.