Fuzzy Logic in Non Destructive Testing of Aerospace Structures

In nondestructive testing to locate the faults we send an ultrasonic signal and measure the resulting vibration at di erent points To describe and combine the uncertainty corresponding to di er ent measurements and fuzzy estimates we used fuzzy logic As a result we get reasonably simple computa tional models which lead to as good fault detection as the known more complicated models I Nondestructive Testing Is Important One of the most important characteristics of the plane is its weight every pound shaved o the plane means a pound added to the carrying ability of this plane As a re sult planes are made as light as possible with their skin as thin as possible However the thinner the layer the more vulnerable is the resulting structure to stresses and faults and ight is a very stressful experience Therefore even minor faults in the plane s structure if undetected can be disastrous To avoid possible catastrophic conse quences before the ight we must thoroughly check the structural integrity of the plane Some faults like cracks holes etc are external and can therefore be detected during the visual inspection However to detect internal faults cracks holes etc we must somehow scan the inside of the thin plate that forms the skin of the plane This skin is not transparent to light or to other electromagnetic radiation very energetic radiation e g X rays or gamma rays can go through the metal but it is di cult to use on such a huge object as a modern plane The one thing that easily penetrates the skin is vibra tion Therefore we can use sound ultrasound etc to detect the faults Usually a wave easily glosses over ob stacles whose size is smaller than its wavelength There fore since we want to detect the smallest possible faults we must choose the sound waves with the smallest possi ble wavelength i e the largest possible frequency This frequency is usually higher than the frequencies that we hear so it corresponds to ultrasound Ultrasonic scans are indeed one of the main non destructive NDE tools see e g In nondestructive testing of structural integrity we send an ultrasonic signal to the tested system and measure the resulting vibration at di erent points Our goal is to detect the points where the cracks or other possible faults are II Modal Approach to Nondestructive