2020 Volume 66 Issue 2 Pages 59-66
The purpose of this study was to confirm the influence of electron-beam (EB) irradiation on plastic flow deformation of bulk wood. Flat-sawn specimens of hinoki (Chamaecyparis obtusa) in the oven-dry condition were irradiated by EB at several levels of absorbed dose ranging from 0 to 263 kGy. Free compression tests were performed on the irradiated specimens at moist and heated conditions to obtain stress-strain curves. Young's modulus, proportional limit stress, and flow starting stress obtained from the curves were decreased by increased dosage. It was shown that the EB irradiation caused a decrease in the stress required for flow deformation while smaller decrease for elastic deformation or densification deformation. The proportional limit strain, flow starting strain, and maximum strain in the curves indicated that the EB irradiation promoted the flow deformation, though it did not affect the elastic deformation and densification deformation. The change in shape of specimens during the compression test was also examined. The irradiation promoted the deformation along the tangential direction which was also observed for the non-irradiated specimens. The irradiation also caused deformation along the fiber direction which was not caused in the non-irradiated specimens, and the deformation increased with increased dosage. Observation of the specimen surface using the scanning electron microscope indicated that the deformation along the fiber direction was caused by fracture of the wood fiber due to the EB irradiation.
