Method and apparatus for detecting normal cracks using infrared thermal imaging

A method and infrared thermal imaging apparatus detects normal and angled cracks on or beneath a sample surface using infrared thermal imaging where the crack plane is perpendicular or angled to an imaged surface of the sample. A constant heating source is used for heating a section of the sample to produce a lateral heat transfer through the sample. An infrared camera is positioned near one side of the sample for receiving thermal image data resulting from the lateral heat transfer through the sample. A data acquisition and processing computer is used for acquiring and differentiation processing thermal image data from the infrared camera for generating two-dimensional first derivative and second derivative images to detect the normal and angled cracks.