Fiber reinforced composites full elastic characterization with surface longitudinal waves, using ultrasonic laser...

This study focuses on a non-destructive methodology for the elastic characterization of fiber-reinforced composites. The methodology uses the surface skimming longitudinal wave (SSLW) generated by an ultrasonic probe and detected via laser interferometry. Conventional mechanical and ultrasonic techniques frequently necessitate the use of multiple samples and intricate configurations to estimate the complete elasticity matrix, particularly in the case of anisotropic materials. To address these limitations, we propose a laser-based approach that enables precise measurement of group velocities across a 180°angular sector of a single specimen. The method was validated on isotropic PMMA and applied to two transversely isotropic composites: a unidirectional glass fiber-reinforced epoxy and a short-fiber bone-mimetic composite. A polar scanning scheme illustrated in B-scan, in conjunction with high-resolution time-of-flight analysis, enabled the extraction of SSLW velocities with a high degree of accuracy. These experimental velocities were then used in an inverse optimization algorithm based on Christoffel equations to retrieve four out of five independent elastic constants. The results showed strong agreement with contact-mode ultrasonic measurements and theoretical models. Furthermore, the method enabled the estimation of the principal anisotropy direction in a composite with unknown fiber orientation, thereby demonstrating the robustness and versatility of laser interferometry for comprehensive elastic characterization of composite materials.