Effect of samples preparation methods on mechanical properties of wood, 1: Effect of period and temperature of water storage, and cooling rate after heating on water-swollen wood
2004
Kamei, K. (Kyoto Prefectural Univ. (Japan)) | Ishimaru, Y. | Iida, I. | Furuta, Y.
The effects of storage period and water temperature after vacuum water impregnation, and cooling rate to 20 deg C, after heating to 80 deg C, on the mechanical properties of water-swollen hinoki wood (Chamaecyparis obtusa) were investigated mainly by means of stress relaxation measurements. The stress relaxation of water-swollen wood decreased rapidly in the early stage and then slowly approached an equilibrium rate of relaxation with increasing period of water storage at 20 deg C for 90 days or more. Rate of decrease of stress relaxation accelerated with an increasing temperature of water in which water-swollen wood was kept. Above 60 deg C the effect of water storage period on stress relaxation behavior was hardly recognized. When the water-swollen wood was cooled to 20 deg C after heating to 80 deg C, stress relaxation increased and modulus of elasticity (MOE) deceased with increasing cooling rate, but the extent of the increase in relaxation was much greater than that of the decrease in MOE. The difference in the relaxation caused by different cooling rate was not diminished at 40 days after cooling. The above results suggest that destabilized wood, after being subjected to changes in moisture content and/or temperature, becomes stabilized with a progress of time, and that the stabilizing rate is accelerated at higher temperatures. The effect of destabilization is more clearly evident in stress relaxation, i.e., in fluidity, than in elasticity.
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