NDE OF IMPACT DAMAGE IN SANDWICH STRUCTURES USING ULTRASONIC, THERMOGRAPHY AND LASER SHEAROGRAPHY

摘要

In this paper, the capabilities of thermal and vacuum shearography and pulsed thermography are compared with conventional pulse-echo and through-transmission ultrasonic methods using honeycomb composite samples with simulated defects as well as real impact damage. It is shown that the pulse-echo ultrasonic can detect skin delamination while the through-transmission ultrasonic can detect the total impact damage but cannot distinguish between the delamination and the core damage. Similarly vacuum shearography can identify the total damage while pulsed thermography and thermal shearography only show the skin delamination but not the core damage when the sample is in the "dry" condition. However, when moisture is allowed to penetrate into the honeycomb core, it is possible to detect the core damage using these methods. It is also shown that reference samples containing Teflon and other inserts that are developed for the calibration of ultrasonic equipment may not be appropriate for thermography or shearography techniques.