Imaging features of different defects in metals using laser ultrasonic techniques

• The imaging features of six different defect using laser ultrasonic techniques were studied. • The numerical model was established using the discontinuous Galerkin finite element method. • The defect imaging features on B-scan maps were validated experimentally. • The quantitative inspection method for internal pore and crack defect were proposed. Different types of defects such as pores, porosity, cracks in different directions, have various impact on the load bearing capacity and fatigue strength of metal components used in the field of aerospace, rail transportation, electrical equipment, etc. Therefore, feature recognition and classification of defects contribute greatly to the performance evaluation of the metal components. In this paper, the imaging features of six typical defects in metals were obtained by using laser ultrasonic (LU) scan inspection techniques. First, the numerical models of LU inspection of different defects were established based on the discontinuous Galerkin finite element method (dG-FEM) in COMSOL/Multiphysics. Then, multiple groups of FE simulations were carried out. The generation and receiving lasers were moved along the scanning direction according to a fixed step during the simulation. All the simulated A-scan signals were stacked up and plotted in the B-scan and D-scan maps. At last, six samples with different artificial defects were manufactured for the LU inspection experiment. The defect imaging features in the experimental B-scan maps are consistent with the numerical results. Besides, the mathematical calculation methods of defect position, dimension and orientation were put forward.