Investigation on Fructure Phenomena of Large Wood Construction Menber using a Measurment Technique of Crack-Propagation

研究了胶合层对层积材弯曲疲劳裂纹扩展的影响。胶粘剂的种类有间苯二酚树脂胶粘剂和水性高分子异氰酸酯胶粘剂。标本由直径约90厘米的贝壳杉原木制成。对试样施加完全反向的弯矩。应力循环的频率为每秒30次。所得结果如下。（1）具有粘结线的试样在裂纹扩展曲线的第二阶段（稳定阶段）的区域中显示出大的影响。在第二阶段，最大影响出现在试样宽度的20%左右.（2）两条粘合剂线比一条粘合剂线显示出更多的失效循环次数。（3）出现裂纹扩展线穿过胶层的状态。（4）水性高分子异氰酸酯胶粘剂与间苯二酚树脂胶粘剂在失效循环次数方面基本相同。

The effect of adhesive line on the bending fatigue crack-propagation for laminated wood was investigated. Kinds of adhesive were Resorcinol resin adhesive and Aqueous Polymer isocyanate adhesive. Specimen were prepared from Agathis log about 90 cm in diameter. A completely reversed bending moment was applied to the specimen. The frequency of the stress cycles was 30 cycles per second. The results obtained are as follows.(1)Specimens having the adhesive line show the large effect in the region of the second stage (the stable stage) of the crack-propagation curve. In the second stage, the maximum effect appears on about 20 % of the specimen width.(2)Two adhesive line shows much more in number of cycles to failure than one adhesive line.(3)The state of the crack-propagation line across adhesive lines is appear.(4)Aqueous polymer isocyanate adhesive shows much the same as Resorcinol resin adhesive in number of cycles to failure.