Date of Award

2004

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

Robert W. Rice

Second Committee Member

Barry Goodell

Third Committee Member

Vincent Caccese

Abstract

This study investigated using ultrasonic testing and analyses techniques to determine their feasibility for defect detection in spruce lumber. Experiments were conducted in the radial direction in lumber and the effect of induced defects on ultrasonic wave characteristics were determined. Ultrasonic velocity was found to be ineffective due to changes in wavelength and frequency when large defects are present. Amplitude, peak frequency magnitude and area under the frequency spectra showed statistically significant differences between clear and defect bearing samples, but the variation in properties was found to be too high for these methods to be effectively applied. Variation I the data was attributed to inherent variation in the material and related to density and microstructure. When sound intensity level, a parameter that includes density, was calculated, variation between samples decreased to a level where distinctions could be made between clear and defect bearing wood, both within and between samples. Analyses and comparison of the frequency spectra showed clear changes with the introduction of defects. This study also investigated whether ultrasound could be used as an indicator of the moisture content in frozen and unfrozen spruce lumber. Initial experimentation indicated that velocity and the attenuation coefficient of ultrasonic waves would be the best methods to determine moisture content. Experiments to determine ultrasonic velocity in the radial direction were conducted at five different moisture content levels and three moisture levels were used for attenuation testing. The results show that a strong inverse relationship exists between ultrasonic velocity and moisture content in both frozen and unfrozen lumber. The wave velocity in frozen wood was consistent and about five percent greater in frozen wood than in unfrozen wood. The relationships existed both above and below fiber saturation and the differences were statistically significant. The attenuation coefficient decreased with a decrease in moisture content in both frozen and unfrozen lumber. Furthermore, no statistically significant difference was found between the attenuation coefficient in frozen and unfrozen lumber at the three moisture levels. While the main research effort centered on the difference in wave velocity between frozen and unfrozen wood at specific moisture content levels, a study was also done to determine the effect of temperature of on ultrasonic velocity. Ultrasonic velocity decreased linearly with an increase in temperature. The findings of this study suggest that both ultrasonic velocity and the attenuation coefficient can be applied as moisture indicator in either frozen or unfrozen lumber.

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