Ultrasonic Guided Waves Based Method for Shm – Simulations and an Experimental Test

Guided waves based methods are widely used for damage detection and localization in metallic and composite structures. Success of the method application depends on many factors like sensors/actuators location, sensor electronic system design, sensor shape, frequency range of excitation waves and applied signal processing procedures. Authors developed new modified LISA and EFIT algorithms to solve guided waves propagation problem in metallic and composite structures. Developed procedure helps to simulate wave propagation for damaged and undamaged structures for different configuration of sensors and actuators locations, shapes of sensors and frequency range. Simulation results helped to design system including hardware and software for monitoring and diagnostics of plate-like structures. Time and frequency domain methods are implemented in the system for damage detection. The simulation results have been validated using experimental test of aluminum and composite structures with different sensor/actuators configuration. New SHM system design based on formulated method and its application for real mechanical structures will be presented. Introduction Lamb waves are widely used in SHM applications to plate-like structures. The ability of waves to travel over long distances enables inspections of wide areas in short time. Since Lamb waves propagation is a rater complex phenomenon when a Lamb wave based SHM system is designed many factors should be taken into account. Made up of a superposition of longitudinal and shear waves, Lamb waves can propagate in both symmetric and anti-symmetric modes. Infinite number of modes can exist in a plate. The dispersion relation can be found for isotropic materials from Rayleigh-Lamb frequency equation roots:      2 2 2 2 4 tan tan q k qp k ph qh    (1)       qp k q k ph qh 2 2 2 2