An instrument designed to measure the a-c field accurately has been built and fully tested on steel, aluminium, and titanium. These field measurements can be interpreted in terms of crack size, which provides a new technique for nondestructive testing (NDT) that requires no prior calibration. This paper describes the basic electronic measuring system, theoretical derivations of the electrical-field distribution, and application to industrial problems such as crack measurement in threads, shafting, welded connections, etc.
Resonance effects are among the most intriguing phenomena in physics and engineering. The classical case of a mass-spring oscillator driven at its resonant frequency is one of the earliest examples that students encounter. Perhaps the most commonly depicted method of driving the vibrating system is mechanical. An alternative approach presented in this paper describes an electromagnetic driver that is convenient to use and that provides a frequency resolution of 0.001 Hz. A common mass-spring arrangement suspended vertically with a linear array of permanent magnets located at the bottom of the system is used for illustrating the technique.1
A torsion oscillator is a vibrating system that experiences a restoring torque given by τ = −κθ when it experiences a rotational displacement θ from its equilibrium position. The torsion constant κ (kappa) is analogous to the spring constant k for the traditional translational oscillator (for which the restoring force F is proportional to the linear displacement x of the mass). An effective torsion oscillator can be constructed by integrating a spring's translational harmonic properties into an Atwood2 arrangement where a disk serves as the pulley for the system and the spring(s) exert restoring torques on the oscillating disk. Both effective torsion constants and effective spring constants can be expressed in terms of adjustable parameters of the system. These expressions enable one to theoretically describe the motion of the hybrid oscillator and to calculate its period. A comparison of the translational and rotational interpretations teaches of their analogous mathematical properties and challenges the intuitive skills of those considering such systems.
This report has been prepared by the U.S. Department of Energy (DOE) as part of a Research Development Demonstration Testing and Evaluation (RDDT&E) project by EG&G Energy Measurement's (EG&G/EM) Remote Sensing Laboratory. lt examines geophysical detection techniques which may be used in Environmental Restoration/Waste Management (ER/WM) surveys to locate buried waste, waste containers, potential waste migratory paths, and aquifer depths. Because of the Remote Sensing Laboratory's unique survey capabilities, only those technologies which have been adapted or are capable of being adapted to an airborne platform were studied. This survey describes several of the available subsurface survey technologies and discusses the basic capabilities of each: the target detectability, required geologic conditions, and associated survey methods. Because the airborne capabilities of these survey techniques have not been fully developed, the chapters deal mostly with the ground-based capabilities of each of the technologies, with reference made to the airborne capabilities where applicable. The information about each survey technique came from various contractors whose companies employ these specific technologies. EG&G/EM cannot guarantee or verify the accuracy of the contractor information; however, the data given is an indication of the technologies that are available.
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