Cooling set and its recovery in water-saturated bamboo under large bending deformation

To clarify the bending properties and cooling set for bamboo under large deformation, the relationship between applied deflection and residual deflection was investigated, and comparison was made with the results of thermal recovery and anatomical changes due to deformation. No clear effect of initial deflection on set measured after a long time was found for wood and bamboo loaded on the epidermis side (Bepi). On the other hand, set for bamboo loaded on the endodermis side (Bendo) increased with deformation level. Recovery from the deformation with time for Bendo was almost complete at around 1000 min after unloading in the three-point bending method. This recovery behavior was not seen for Bepi or wood. It was considered that no failure was caused in the bent specimen, because most of the deformation was completely recovered by reheating to the temperature at which the specimens were deformed before cooling. The recovery from deformation for B_endo loaded by the four-point bending method continued even after 1000 min. From microscopic observations, shearing deformations were seen for Bendo loaded by the three-point bending method. From these results, it can be considered that shearing deformations between the two loaded points effectively contribute to decreased recovery force from deformations for B_endo. Part of this report was presented at the 54th Annual Meeting of the Japan Wood Research Society in Sapporo, August 2004