Enhancing Laser Ultrasonic NDT in Metals: A Glass Confinement Layer Approach

Laser ultrasonic technology holds significant potential in the field of non-destructive testing of materials [1-3]. Its wide bandwidth and high spatial resolution allow for the sensitive detection of small defects inside materials, crucial for assessing the integrity and safety of components [4-7]. Furthermore, laser ultrasonic technology can be applied in scenarios where traditional ultrasound detection methods are not feasible or challenging to implement, such as online monitoring of rotating objects [8], detection of complex structures with large curvature, such as turbine blades, wings, and drill bits [9, 10], and testing under extreme environments with high temperature and high pressure [11-14]. However, it has been reported nearly 30 years ago that the constrained surface can produce stronger longitudinal effects, yet the practical application of the constrained surface method has been limited [15]. This limitation arises from the comparatively low intensity of ultrasound signals generated by the thermoelastic mechanism, particularly the weakened bulk wave in metals [16-20]. As a result, the non-destructive testing capability of laser ultrasonic technology within metal materials is constrained. Therefore, this study introduces a glass confinement layer to enhance the excitation efficiency of longitudinal waves and explores its application in locating deep internal defects within metals.