Nail and Screw Withdrawal Strength, MOE and MOR in Densified Poplar Wood

This research has been conducted to investigate the influence of steam temperature and densification percentage on withdrawal strength of nail and screw joints as well as flexural strength in compressed wood of eastern cottonwood (Populus deltoeides). For this purpose 15 healthy standing trees of eastern cottonwood were selected from Dr. Bahramnia forest located in Shasht-Kola (Gorgan). The flatsawn samples were selected and prepared from defect free parts of sapwood. Densification was done at 4 percentages, namely 20%, 30%, 40% and 50%. Steaming treatment was selected at 3 temperature levels, 120, 140 and 160 °C for this purpose. Density, withdrawal strength of nail and screw joints and also flexural strength (MOR and MOE) of compressed specimens were measured. Also, the microscopic images of compressed samples were studied. The results showed that the percentage of densification may significantly influence the density of samples, especially at the higher percentages. Furthermore, it was found that the amount of densification has significant influence on the withdrawal strength of nails (up to 220%) and screws (up to 120%). Regarding the flexural strength, MOR and MOE possessed higher amount as their amount were increased by 70% and 40%, respectively, compared with control samples. In addition, the microscopic images showed that more homogenous material could be obtained at higher densification percentages.