木口円盤の収縮と割れの発生

Abstract

木材の横断面における収縮異方性に基づいて, 木口円盤の乾燥過程で発生するV型割れの実態を把握するために, アカマツおよびブナの生材木口円盤の乾燥過程における収縮と割れ発生の経時変化を観察, 測定した。収縮率の測定には新しく考案したブリッジ型ひずみゲージを用いた。円盤木口表面の細かい割れはほとんど収縮が認められない乾燥初期にすでに多数発生し, そのうちの数個が収縮率が急激に増大する時期にV型割れにまで発達する。しかし, 収縮がほとんど停止する乾燥終期には, 1 - 2個の大型のV型割れを残して, 大部分の割れは閉鎖するか狭くなる。

The restrained shrinkages of cross sectional disks from Akamatsu (Pinus densiflora Sieb. et Zucc.) and Buna (Fagus crenata Blume) of about 10 cm in diameter and 15 mm in thickness were determined in relation to the V-shaped crack formation caused by the transverse anisotropic shrinkage of wood during drying. Bridge-type strain gauges newly deviced and calibrated were fixed on the disks for measurement of the radial and tangential shrinkages. The shrinkage measurement and the observation of check and crack formation were carried out during drying test at 60℃. Many fine checks develop on the disk surfaces at early stage of drying. Some of the checks transfer V-shape cracks during a period when the shrinkage of disk ceases, then the most of cracks and checks disappear or reduce, leaving one or two large V-shape cracks.