Laser ultrasonic techniques and numerical models for damage and degradation tracking in FRP composites

A combined analytical and experimental work is described to demonstrate the application of Laser Ultrasonic techniques for monitoring long term performance (Durability) of thick-section Pultruded FRP composites. Damage is induced in the material using both environmental and mechanical methods. Laser generated Rayleigh Surface waves are used to monitor the health of the composites. The phase velocity of the measured Rayleigh wave is related to the material properties (such as stiffness) that characterize damage and may thus be used to track material changes. 2D-FFT is used to interpret experimental measurements and to track damage in a material system via velocity dispersion measurements. Numerical models, using explicit finite element method, are used to simulate Rayleigh wave propagation on a layered medium of finite thickness with and without microstructural damage. These FEM models are used to investigate damage mechanisms and explain experimental findings. Correlations are drawn between experimental (mechanical and nondestructive) and FEM results. This study demonstrates the effectiveness of the methodology that combines laser ultrasonics, with the 2D-FFT to track the evolution of damage and degradation in thick-section pultruded composite materials.