Total focussing method for volumetric imaging in immersion non destructive evaluation

This paper describes the use of a 550 (25x22) element
2MHz 2D piezoelectric composite array in immersion mode to
image an aluminum test block containing a collection of artificial
defects. The defects included a 1mm diameter side-drilled hole, a
collection of 1mm slot defects with varying degrees of skew to the
normal and a flat bottomed hole. The data collection was carried
out using the full matrix capture; a scanning procedure was
developed to allow the operation of the large element count array
through a conventional 64-channel phased array controller. A 3D
TFM algorithm capable of imaging in a dual media environment
was implemented in MATLAB for the offline processing the raw
scan data. This algorithm facilitates the creation of 3D images of
defects while accounting for refraction effects at material
boundaries. In each of the test samples interrogated the defects,
and their spatial position, are readily identified using TFM.
Defect directional information has been characterized using
VTFM for defect exhibiting angles up to and including 45o of
skew.