Graduate Thesis Or Dissertation
 

A transistorized sonic generator and detector for finding Young's modulus of wooden beams

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/v405sc87x

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  • Young's modulus, often called the modulus of elasticity, gives a measure of the stiffness of a material to an imposed load. The modulus of a wooden beam is most often obtained by destructive tests which destroy the specimen. If a practical method can be found to measure Young's modulus non-destructively, several advantages can be realized: First, any number of specimens can be thoroughly tested and accepted or rejected according to the results of the measurement. Second, a single beam can be tested repeatedly. Finally, a wooden beam already in use can be measured. A background on the measurement of Young's modulus of wooden beams is presented. The standard destructive test is described as are several non-destructive techniques employing acoustics. Examples of non-destructive tests at sonic and ultrasonic frequencies are given. From this background a non-destructive method of testing which makes use of the reactions of a wooden beam when excited at its natural resonant frequency is selected for further study. The mathematical background necessary to interpret the results and to relate them to Young's modulus is developed. Test equipment is set up to determine the practicality of this method. Since this non-destructive method seems feasible, a sonic generator and detector is designed and constructed as a single unit. It is built with the qualifications that it be rugged, compact, easy to operate, and relatively inexpensive. The design calls for a variable frequency oscillator, a ten watt amplifier, excitation and detection transducers, a detection amplifier, and a display meter. The design of the equipment is discussed in detail, and the reliability and accuracy of the apparatus over an extended period of time are predicted. Methods of operation of the sonic generator and detector are discussed, and the results of a short series of measurements made with the equipment are presented.
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