| 研究実績の概要 |
Following established experimental setup for determination of model rheological parameters of Sugi and Hinoki boxed-heart timber, I investigated rupture load of surface and inner layer specimen of the timbers at temperature of 20, 65, 80 and 95°C by using cantilever method inside laboratory temperature and humidity chamber. Rheological behavior of surface and inner layer specimen of Sugi and Hinoki boxed-heart timber at constant moisture content (viscoelastic creep) was investigated at the same condition as describe above using cantilever creep test. A load of 20 % from rupture load of the specimen at each temperature was applied at its free-end and strain gauges were bonded at fourth span (10 mm) on its upper and bottom faces. Four-element burger model was used to model creep behavior of the timbers. Some of the results are as follow: as expected, modulus of rupture (MOR) of all the specimens tended to decrease as temperature increased. From creep test results, it was found also that temperature had significant effects on the creep properties of the timber. Creep compliance of surface and inner layer specimen of both Sugi and Hinoki boxed-heart timber tended to increase as temperature increased. Fitting experimental data with burger model used in this research shows a good agreement. Therefore, model parameters obtained in this research were applicable for identification of creep behavior of the timbers. In addition, surface layer specimen of Hinoki boxed-heart timber retained its elasticity better than that of Sugi boxed-hert timber as temperature increased.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
In research proposal, four species of commercial Japanese softwood boxed-heart timbers will be investigated in this research. However, two species (Karamatsu and Akamatsu) are difficult to find in Kyushu area. In addition, to establish the experimental setup in this research was time consuming due to try and error during assembling the experimental setup and long purchasing time of the equipment.
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| 今後の研究の推進方策 |
Creep investigation will be conducted under varying moisture conditions (mechano-sorptive creep). Two tests under varying moisture conditions will be conducted. First, creep for surface and inner layer specimens of the timbers with an EMC of 12 % will be performed for 4 h at temperatures of 20, 65, 80 and 95 °C; after that, the relative humidity (RH) inside the chamber will be adjusted so that the EMC of the specimen will become 8 % for 20 h. The second test will involve exposing the cantilever specimen to a cycle of rehumidification and drying at temperatures of 20, 65 and 80 and 95°C. Following a 4 h period of creep at an EMC of 8 %, the RH inside the chamber will be adjusted so that the EMC of the specimen becomes 12 % for 4 h, and then the RH will be adjusted again so that the EMC of the specimen becomes 8 % for another 4 h. Finally, the RH inside the chamber will be adjusted so that the EMC of the specimen becomes 12 % for 16 h. For both tests, surface strains of the specimens will be recorded.
Following determination of model parameters of surface and inner layer specimen of the timbers obtained from viscoelastic creep and mechano-sortive creep tests, numerical analysis will be performed to predict stress distribution of the timbers along the thickness. After that, optimization of the drying schedule to minimize the occurrence of defects during the drying of some commercial Japanese softwood boxed-heart timber will be carried out on the basis of the drying stress distribution of the timber along the thickness.
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