The ability to detect and size surface-breaking flaws is key to preventing catastrophic
part failures. Ultrasonic nondestructive evaluation offers a method to detect these
flaws, but thin materials still present challenges due to the potential for wave
superposition. Previous literature has shown that using shear waves offers an
advantage over longitudinal waves for flaw detection in thin materials. This thesis
proposes a method for improved small back surface-breaking flaw inspection by
optimizing the angle of oblique incidence of a shear wave for the maximum received
signal magnitude in a pulse-echo configuration. The ultrasonic response of flaws
in Aluminum 6061 specimens with thicknesses of 6.35 mm (1/4 in) and 3.175
mm (1/8 in) were studied using finite element analysis in ABAQUS. The effect
of crack length, width, tip morphology, and inclination angle were examined to
investigate the impact of varying crack geometry on the magnitude of the received
signal. Crack tip morphology was found to have no effect on the optimal oblique incidence
angle, which was heavily dependent on specimen thickness, crack width,
inclination angle, and length.
