3D ultrasonic inspection of anisotropic aerospace components

Two-dimensional (2D) ultrasonic arrays for non-destructive evaluation will enable the detection and characterisation of sub-surface defects in three-dimensions (3D). This type of volumetric inspection is desirable when testing engineering components that have an inherent 3D internal structure or may contain defects orientated at a range of angles. One potential industrial application for this technology is the in-situ inspection of jet-engine turbine blades for root cracking. However, modern turbine blades are manufactured from single crystals of nickel-based superalloys for the excellent mechanical properties these materials exhibit at elevated temperatures. Single-crystal materials are elastically anisotropic, which causes ultrasonic waves to propagate with different velocities depending on the direction of the wave. If unaddressed, this significantly reduces the quality of the inspection and the 3D images that can be produced with an ultrasonic array. In this paper, a model of wave propagation in anisotropic media is used to correct an ultrasonic imaging algorithm to enable the reliable volumetric inspection of single-crystal aerospace components.