Identification of defects of wood by using wave analysis of tap tone and application to machine stress rating of lumber

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Identification of defects in lumber by a wave analysis of tap tone and application to a machine stress rating of lumber were studied.1. Identification of defects by a wave analysis.A transfer matrix method was used to evaluate the spectrum peak shift due to defects of a specimen. A numerical equation which estimates the spectrum peak shift by defects was obtained. Experiments by using specimens having round holes showed the same tendency as the numerical simulation of the transfer matrix method. The peak shifts of the specimen having multiple holes were evaluated by a linear combination of the effect of individual hole. A new principle to identify the defects positions was proposed. The position was identified so that the coincidence between experimental and estimated values becomes maximum.2. Determination of vibration parameters by a wave analysisA tap tone includes useful information not only in a fundamental vibration but also in higher order vibration waves. Isolation of the wave of an individual mode was done by using the filtering procedure of Fourier transformation. Then Hilbert transformation was adopted to obtain a time envelope and logarithmic decrement was determined. Moreover, an instantaneous frequency given by Hilbert transformation showed a potential of a quasi time-frequency simultaneous analysis of a tap tone.3. Application of wave information to machine stress rating of lumberSmall and full size wood specimens were used. A multiple regression analysis using Young's modulus, logarithmic decrement and irregularity in frequencies of higher ordered vibrations gave higher correlation than the case of a simple regression which used Young's moduli