A Fundamental Study on Characterization of Guided Wave Scattering from Crack under Different Loading Conditions

Ultrasonic Guided wave based inspection technique is one of the useful damage detection techniques. Waves are introduced using Piezo-electric Wafer Active Sensors (PWAS) sensors, which are placed, at discrete locations in order to inspect damages in plates and the idea has the potential to be extended to assembled structures. Various actuator-sensor configurations are possible within the network in order to identify and locate damages. The ability to detect the smallest defects within a material domain depends upon the wavelength of the incident wave, wave propagation characteristics, noise, and uncertainty in various quantities of interest involved. However, complex geometric features in a component also contribute to mode conversions and scattering losses, which make it difficult to distinguish the signal packets in a time signal received at a receiver location. In a component with multiple rivet holes such as fuselage of an aircraft, one of important type of damages that are required to be inspected carefully in such assembled structures are the rivethole cracks and corrosion. Ultrasonic inspection is performed by measuring and characterizing the waves reflected or transmitted through the damage. With no apriori knowledge on orientation of such damages, but only probable zone of high importance of inspection prescribed from the design criteria and loads on the component, the inspection method requires employing complex signal processing algorithms to analyze the data and identify the effect of scattering. In addition, the damages cause varying degree of changes in ultrasonic wave signals. The signals change significantly when crack from a rivet is opened up under load whereas in unloaded condition, cracks are often hard to detect In this study we present the effect of crack under fatigue load on the signal parameters during different loading conditions. We first introduce a single hole on the component and then a fatigue crack is allowed to grow from the hole. We show the effect of growing crack on the ultrasonic signals through amplitude and phase modulation factors. This describes the effect of growing crack with respect to a reference signal measured before the crack was grown.