The paper describes the quantitative determination of the size and the location of a subsurface defect from the phase image of lock-in infrared thermography. Phase (or temperature) difference between a defect area and a sound area indicates the qualitative location and size of a defect. To accurately estimate those, the paper proposes a shearing phase technique in which the inspected image is shifted with a proper pixel size to obtain the shearing image and the subtraction between two images gives a shearing phase distribution. The shearing phase distribution has the maximum, the minimum, and zero point which is a key to quantitatively determine the size and the location of subsurface defect. Experimental results of steel plate with artificial defects show good agreement with actual values.

This paper describes an optical nondestructive testing technique for honeycomb composite material, which has been used as structural material in aeronautics and space transportation. The inspection of a honeycomb composite structure by the conventional NDT technique is difficult and complex. Optical NDT can give a solution about problems of previous technique. Optical NDT basically provides non-contact, whole-field inspection and easy interpretation. Representative techniques are X-ray, Thermography, Electronic Speckle Pattern Interferometry (ESPI), Shearography, Neutron Radiography and so on. They each have strengths and weaknesses with respect to system preparation, field application and inspection target. ESPI, ultrasonic testing and Thermography in this paper are applied to detect an artificial defect of 30 mm in diameter and an impact- induced delamination inside the honeycomb composite plate, which consists of an aluminum core and carbon fiber reinforced plate skin. Inspection conditions in the experiment are compared with each other, and results are discussed.