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Intermittent wiring faults are among the most frustrating, time consuming, and expensive problems to diagnose in electrical systems. These sporadic problems occur when wires are wet, vibrating, under pressure, or when the system is in a particular configuration during use. Then when the system is stable and/or powered down, the problems disappear. The best and often the only time to locate these faults is while the faulty wiring is live and in operation. This paper will describe new technology for locating intermittent faults on live wiring systems without interfering with their operation. Spread spectrum time domain reflectometry (SSTDR) has been developed for locating these intermittent faults on live aircraft wires. A pseudo noise (PN) code is injected on the wire, well below the noise margin of the system. The PN code can be self-correlated to give the characteristics of the wiring system - its branches, loads, sources, etc.

A method is presented which permits the prediction of fatigue or static strength notch factors for notches of any acuity in metal parts, using as a basis conventional tensile properties and a “Neuber constant” which expresses size effect. Extensive experimental verification is presented, with special emphasis on the crack strength of sheet metal. While the method is devised as an aid to design, it has great potential usefulness as an aid in materials testing to define fatigue or static notch sensitivity. Extensions of the method to stiffened flat sheet and to pressurized cylinders are discussed.

THE history of the box-beam problem is outlined. This problem has interested naval architects for a long time, but no design methods suitable for aeronautical applications have been evolved. The advent of stressed-skin construction in aeronautics has necessitated further development of the theory. The problem of redistribution of bending stresses caused by shear deformation on the cover sheet, which cannot be avoided even in the most favorable cases, is considered as the most fundamental problem in box-beam design. Simplifying assumptions are discussed that permit a mathematical approach to the problem. Solutions for special cases finally are combined into a method of analysis intended chiefly for box-beam wings. Analytical formulas are given for a simple case. With the help of these formulas, various structural arrangements of a small transport-size wing are compared.