Line scan versus flash thermography: comparative study on reinforced carbon-carbon

Abstract

Thermographic inspection techniques fundamentally vary by method of heat deposition. Some systems use a short burst of energy from a flash lamp while others control the motion of a quartz lamp over the material. Both techniques have had a history of successful inspections on aircraft and boiler tubes, for example. Historically, the system used for inspections was determined by the thermographic equipment available to the researcher. This paper will compare the flash and line scan thermographic systems on Reinforced Carbon-Carbon. Reinforced Carbon-Carbon (RCC) is a brittle composite material that is found on the Space Shuttle’s nose section, wing leading edges, and chin panel. It is used to protect the orbiter’s aluminum frame from superheated air during flight. In the time since the Columbia accident, impact tests on RCC panels have been ongoing. Flash thermography has been successfully used to scan the impact site for delaminations. While the system has proven effective, it is not without limitations. A single scan yields only that section of material that is in the field of view of the infrared camera. Additionally, delaminations deep within the material may not be resolved as well as with quartz heating. A comparative study was conducted using a RCC panel with flat-bottom holes varying in diameter and depth. The panel was scanned with the Thermal Line Scanner, the Thermal Photocopier, and the Echotherm from Thermal Wave Imaging. Signal to noise ratios were calculated for the defects and used to compare the three systems. This paper will discuss the details of the study and show the results obtained from each of the three systems.