MECHANICAL HYSTERESIS AS AN NDE TOOL FOR EVALUATING COMPOSITE HONEYCOMB DAMAGE

Honeycomb composites are finding ever increasing use on aircraft structures, making nondestructive detection of defects contained within honeycomb structures all the more important. This paper focuses on a new detection technique which makes use of the mechanical hysteresis seen as loops in the force-displacement curves. It was observed from load test data that internal damage in honeycomb sandwiches causes the average slope of the force-displacement curves to decrease and the area contained within the hysteresis loop to increase. To satisfy the inspection speed and one-sided access requirements of NDE techniques, a dynamic loading approach was pursued where an accelerometer was used to tap the surface of the test sample. Much of the research focused on the deduction of the force-displacement curves from an acceleration curve. This greatly increased the speed of the technique as well as reduced it to a one-sided test, where only access to the outer surface of the structure is needed.