ESTIMATION OF MOISTURE-CONTENT OF LUMBER AND LOGS USING HIGHER NATURAL FREQUENCY OF LONGITUDINAL VIBRATIONS

The methods of evaluating the moisture content (u) of lumber and the w eight (or moisture) change ratio (DELTAW(i)) of logs and lumber with h igher natural frequencies of longitudinal vibrations measured under pi ling were investigated. This is based on the fact that the higher natu ral frequencies of logs and lumber measured under piling was hardly af fected by the piling and that the correlation was observed between the change of natural frequency during the drying process and weight loss due to desorption of water. The specimens used in this study were sug i (Cryptomeria japonica D. Don) wood. The results are summarized as fo llows: 1) The estimated moisture content (u(e)) of lumber was calculat ed by Eq. (3). u(e)s were obtained by substituting the fourth natural frequency (F(c)4) of longitudinal vibration measured under piling into the natural frequency, by substituting mean value of oven-dry weight of all lumber into W(o) and by substituting 1 into K(DELTA)V. As a res ult, the correlation coefficient observed between u(e) and u was 0.951 , and the standard error of u(e) to u was 10.3 (average value of us wa s 50.6%). To obtain greater estimation accuracy, it is necessary to co ntinue analyzing estimated values of W(o) and KDELTAV. 2) The estimate d weight (or moisture) change ratio (DELTAW(ei)s) of logs and lumber w ere calculated by Eq. (4). DELTAW(ei)s were obtained by substituting F (c)4 into the natural frequency and by substituting 1 into KDELTAV. As a result, the correlation coefficient observed between DELTAW(ei) and DELTAW(i) was 0.980 f or logs and 0.973-0.992 for lumber, and the sta ndard error of DELTAW(ei) to DELTAW(i) was 0.754 for logs and 0.774-1. 38 for lumber (average value of DELTAW(i)s was 9.05 for logs and 20.6- 41.6 for lumber). According to these fact, within the limits of u in t his experiment, it seems possible to estimate the tendency of moisture change by only measuring the higher natural frequency of longitudinal vibration of logs and lumber under piling.