Laser-Excited Acoustics for Contact-Free Inspection of Aerospace Composites

Abstract

Ultrasonic testing (UT) is widely used for the nondestructive testing (NDT) of composite materials in the aerospace industry. Liquid-coupled piezoelectric ultrasonic transducers are the most common technology used in this field; however, liquid coupling agents are not always practical, economical, or compatible with materials that cannot get wet. Alternative couplant-free technologies such as air-coupled ultrasound or laser ultrasound (LUS) are available, but either lack the required sensitivity and resolution, or are very costly, large, and sensitive to surface condition and properties. In this paper, we introduce a new couplant-free approach using laser excitation and a commercially available optical micro-phone. This technique is termed laser-excited acoustics (LEA) NDT, which combines the advantages of a contact-free ultrasound technology with the potential for improved sensitivity and resolution required for NDT in industrial environments. We will demonstrate the capabilities of LEA on aerospace composite parts made of carbon and glass fiber–reinforced polymer (CFRP/GFRP) under realistic conditions.