Thermographic Qualification of Graphite/Epoxy Instrumentation Racks

A nondestructive evaluation method is desired for ensuring the 'as manufactured' and 'post service' quality of graphite/epoxy instrumentation rack shells. The damage tolerance and geometry of the racks dictate that the evaluation method be capable of identifying defects, as small as 0.25 inch 2 in area, over large acreage regions, tight compound radii and thickness transition zones. The primary defects of interest include voids, inclusions, delaminations and porosity. The potential for an infrared thermographic inspection to replace ultrasonic testing, for qualifying the racks as 'defect free' is under investigation. The inspection process is validated by evaluating defect standard panels built to the same specifications as the racks, except for the insertion of artificial fabricated defects. The artificial defects are designed to match those which are most prevalent in the actual instrumentation racks. A target defect area of 0.0625 inch 2 (a square with 0.25 inch on a side) was chosen for the defect standard panels to ensure the ability to find all defects of the critical (0.25 inch squared) size.