a new thermal contrast for non-destructive thermographic testing of materials

Abstract

It is known that methods of thermographic non destructive testing (TNDT) based on thermal contrast are strongly affected by non-uniform heating at the surface. Hence, the results obtained from these methods considerably depend on the chosen reference point. The differential absolute contrast (DAC) method was developed to eliminate the need of determining a reference point that defines the thermal contrast with respect to an ideal (sound) area. Although DAC is very useful at early times, the DAC accuracy decreases at later times when the heat front approaches the sample rear face. In this article, a new DAC version is proposed by explicitly introducing the sample thickness and using the thermal quadrupoles theory. It is shown that the validity of the new DAC version increases for long times while being preserved at short times.