NUMERICAL SIMULATION OF LASER EXCITED 3D ACOUSTIC FIELD OF SEMI-INFINITE ISOTROPIC SOLID

Laser ultrasonic technique is an advanced development of the traditional ultrasound technique. Compared to the traditional ultrasonic technique, it has advantages such as non-contact detection. In this paper, an isotropic semi-infinite solid is employed as the theoretical model to analyze the acoustic field generated by the laser pulse. The differential equations are solved with 3D Fourier transform and then 3D inverse fast Fourier transform is used to obtain the displacement field. On the other hand, the model for the finite element simulation should be an aluminum plate with larger thickness. The laser pulse is simplified as a normal force. In both calculation and simulation, it can be observed that laser excited ultrasounds will propagate along the surface of the specimen and inside the specimen. This work has laid out the theoretic foundation for the analytic solution of the 3D acoustic field of a semi-infinite isotropic solid with defects. Based on the finite element simulation of the laser excited acoustic field for the specimen with or without defects, the inverse problem is going to be carried out to determine the size and location of a certain crack.