Investigation of EMAT Base System for the Detection of Bolt Hole Type Cracks. Part 1. Detection of Cracks in the Inaccessible Lower Half of Wing Lap Joints Using EMATS

Abstract : The detection of saw slots in an aircraft wing lap joint is demonstrated with EMATS (Electromagnetic acoustic transducers) utilizing 250 KHz horizontal shear acoustic waves reflected from the fastener area. A real-time Fourier transform signal processor was developed and used to gather experimental data and generate plots of power vs. frequency as well as the complex transform. A simple ultrasonics model is described which is capable of explaining many of the features of the experimental data.