Longitudinal Vibration Test for the Use of a Circular Truncated Cone as a Log Model of Japanese Cedar

The appropriate diameter ratio of log top and butt ends when using a round bar (cylinder shape) as a log model for estimating the density and Young’s modulus of a log was investigated. Square timbers of Japanese cedar (Cryptomeria japonica D. Don) with a length of 1200 mm were used as specimens and were machined into circular truncated cones. A longitudinal vibration test was performed to obtain the Young’s moduli of the square timbers and the circular truncated cones. The Young’s moduli were calculated using the circular truncated cone model and the round bar model. The density and Young’s modulus calculated by the circular truncated cone model were similar to those of the square timbers. Hence, it is considered that the circular truncated cone was effective for estimating the densities and Young’s moduli of logs. The density and Young’s modulus calculated by the round bar model differed from those of the square timbers when the diameters of the top ends were small. However, it is considered that the round bar can be used as a log model for actual logs.