Infrared Detection of Defects in Powder-Metallic Compacts

Abstract

Electric Joule heating of low-conductivity media through direct current excitation can be used to generate a temperature profile throughout a powdermetallic (P/M) compact. When recording the surface temperature distribution with an infrared (IR) camera important information regarding the integrity of the sample can be gained.

Unlike most existing IR techniques, this research concentrates on obtaining the temperature distribution and heat flow behavior in P/M parts when they are subjected to active electric current injection. The practical measurements are supported and complemented by a simple theoretical model that serves as a calibration tool to aid in the evaluation of the infrared signatures that are recorded over the sample surface and correlated with the detection of surface and subsurface flaws.

In this paper we will report on the design of the active infrared detection system and a basic theoretical testbed that is suitable for calibration. Specifically, we state the governing equations and boundary conditions, followed by devising numerical solutions that enable a comparison to the measured thermal response. In addition, the numerical modeling approach can also serve as a method to model various flaw sizes and orientations in an effort to practically determine flaw resolution limits as a function of minimally detectable temperature distribution.

Preliminary measurements with controlled and industrial samples indicate that this IR testing methodology can successfully be employed to inspect both green-state and sintered P/M compacts.