Laser ultrasonic detection of defects in a regular tetrahedral lattice structure based on finite element modeling

Lattice structures possess advantages such as ultra-lightweight, high strength, and high stiffness. However, they often exhibit defects during manufacture and service. Due to the complexity of their structure, detecting these defects can be challenging. Laser ultrasonic technology has emerged as a promising detection method, particularly suited for lattice structures. In this paper, a regular tetrahedral lattice structure model is established, and the finite element method is employed to analyze the propagation characteristics of laser-induced ultrasonic waves within the structure and investigate the impact of various defect types on these ultrasonic waves. Firstly, the thermodynamic coupling model for laser-induced ultrasonic waves in the lattice structure is established and the propagation rules of ultrasonic waves at different locations is discussed. Secondly, the models for different types of lattice structure defects are created and the effects of defect location and depth on ultrasonic wave propagation are analyzed. The results indicate that the modes of ultrasonic wave propagation in the upper sandwich plate are shear wave, longitudinal wave, and Rayleigh wave, while the ultrasonic wave propagation on the surface of the support rod is characterized as longitudinal wave. When the defect is present on the support rod, positioning the probe points directly above the defect on the support rod proves to be highly effective for detection. Furthermore, when cracks occur at the junction between the support rod and the upper sandwich plate, distinct reflected wave can be observed on the upper surface of the upper sandwich plate. Additionally, as the depth of the crack increases, the amplitude of the reflected wave progressively rises, exhibiting a nonlinear trend.