Vibration Modes of Logs Measured by TV Holography

Sondre Skatter, Astrid Aksnes Dyrseth


Resonant vibrations of softwood logs were examined using TV holography. This technique allows a resonance to be detected in real time when the frequency is varied. Time-averaged measurements can be taken to map the spatial vibration pattern of the object both at resonance and at an arbitrary frequency. The resonant frequency of an identified vibration mode is used to calculate certain material parameters. Here, the longitudinal modulus of elasticity is determined from bending modes using Timoshenko's beam theory, and one of the shear moduli is determined from torsion modes. Additionally, the vibration patterns may reflect inhomogeneities within the logs. A feasibility study was made on the possibilities of detecting knots from the vibration patterns of a particular mode of vibration. It was concluded that this is not. in general, possible.


Vibration analysis;TV holography;logs;bending;torsion

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