Interval Approach to Non-destructive Testing of Aerospace Structures and to Mammography

One of the most important characteristics of the plane is its weight: every pound shaved oo the plane means a pound added to the carrying ability of this plane. As a result, planes are made as light as possible , with its \skin" as thin as possible. However, the thinner the layer, the more vulnerable is the resulting structure to stresses and faults, and a ight is a very stressful experience. Therefore, even minor faults in the plane's structure, if undetected, can be disastrous. To avoid possible catastrophic consequences, before the ight, we must thoroughly check the structural integrity of the plane. 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 diicult to use on such a huge object as a modern plane. The one thing that easily penetrates the skin is vibration. Therefore, we can use sound, ultra-sound, etc., to detect the faults. Usually, a wave easily glosses over obstacles whose size is smaller than its wavelength. Therefore, since we want to detect the smallest possible faults, we must choose the sound waves with the smallest possible 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-Aerospace Integrity Testing is Very Time-Consuming and Expensive One possibility is to have a point-by-point ultra-sound testing, the so called S-scan. This testing detects the exact locations and shapes of all the faults. Its main drawback, however, is that since we need to cover every point, we get a very time-consuming (and therefore, very expensive) testing process. A faster idea is to send waves through the material so that with each measurement, we will, be able to test not just a single point, but the entire line between the transmitter and the receiver. To make this procedure work, we need special signals called Lamb waves. There are other testing techniques. All these techniques aim at determining whether there is a fault, and if there are faults, what is the location and the size of each fault. How Can We Save Time and Money? In …