Laser ultrasonics for nondestructive testing of composite materials and structures: A review.

This paper presents a comprehensive overview of Laser Ultrasonic Testing (LUT) and its applications in composite materials. The working principles of LUT are thoroughly explained, and an assessment of its advantages and drawbacks is provided. The mechanisms of wave generation and detection are described, along with their influence on the capabilities and limitations of LUT. The paper includes an inclusive overview of each LUT application in composite materials, highlighting their potential, challenges, and research gaps. LUT is a noncontact and nondestructive technique that utilizes lasers to generate and detect ultrasonic waves, with the material itself acting as an emitting transducer. This unique noncontact approach offers an accurate, versatile, convenient, and rapid method for inspecting and characterizing materials. However, some challenges and research gaps have hindered its widespread adoption. One significant challenge in LUT is the low signal-to-noise ratio (SNR), which becomes more pronounced in composite materials due to their low ablation threshold and high wave attenuation. Furthermore, the characterization and inspection of composite materials are more intricate due to their anisotropy and complex damage patterns. Despite these challenges, the combination of ultrasonic waves capable of characterizing and inspecting materials, coupled with the capabilities of lasers and optics for noncontact and real-time operation, presents a promising outlook for the widespread implementation of LUT in Smart Industries and harsh industrial environments, including those with high temperatures, high pressures, or radioactive conditions. This paper contributes to the understanding of LUT's potential and limitations, paving the way for further advancements in its applications.