<title>Systems-based approach to thermographic NDE</title>

Abstract

Although acceptance of pulsed thermography as a tool for nondestructive inspection continues to increase, standards and metrics for performance assessment and procedure development have been slow to follow. Consequently, practical application development is often left to the experience and intuition of the supervisor, and decisions such as heating input power, surface preparation, acquisition time, camera wavelength, integration time, and sensor type are made on a subjective, qualitative basis. Furthermore, quantitative thermographic methods that have been reported generally rely on the ability of the operator to identify a defect free region of the sample, as well as high-speed laboratory cameras that are not practical for many field inspection applications. Because of these limitations, practical application of pulsed thermography is often limited to use as a qualitative complement to conventional point inspection methods (e.g. ultrasound). We have developed a metric for characterization of active thermographic system performance that defines a Thermal Modulation Transfer Function (TMTF), which allows complete characterization of the IR NDE system performance for a given sample type. The TMTF approach allows accurate prediction of peak contrast times, and best-case contrast for defects of a given diameter and depth. We will use the TMTF approach to demonstrate how detection limits and ranges can be established, and how these limits can be improved using TMTF based signal processing algorithms.