Vibration and propagation characteristics of wood poles subjected to sonic excitation Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8336h533s

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  • The Pacific Coast variety of Douglas-fir was investigated. The samples were tested using both forced and free vibrations. Transverse vibrations were introduced by excitations on the side of the samples. Forced vibrations were applied from 5000 to 0 hertz by a vibration generator, and free vibrations were initiated by a sharp blow from an impacter. By using forced vibrations the transverse resonant frequencies of the samples were determined. An amplitude ratio was created to compare the sound pole to defective specimens. This ratio is zero or near zero for tests on the sound pole. Poles with brown rot had amplitude ratios which were proportional to the size of the decay pockets. Samples with white rot and pitch pockets had ratios which were consistantly greater than 0.1. The results of this research, together with the findings of Professor L.C. Jensen, indicate that brown rot, white rot, and pitch pockets can be detected in Douglas-fir poles by measuring the amplitude ratio. Free vibrations were used to determine the velocity of propagation of the transverse wave in the longitudinal and circumferential directions.
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