INFLUENCE OF WOOD DENSIFICATION ON WITHDRAWAL STRENGTH OF FASTENERS IN EASTERN COTTONWOOD(POPULUS DELTOIDES)

摘要

The aim of this study was to investigate the influence of densification Populus deltoides (eastern cottonwood) on withdrawal strength of nails and screws fasteners. Eastern cottonwood is an imported species from Turkey to Iran, whose young stands were planted, 27 years ago, with distances of 2 m by 3 m inside of a surrounded and specific area, belongs to the educational forest of Gorgan University (North of Iran). Limitation in forest area and available volume of trees makes the provision of new raw materials for the Iranian industries. Hence, there is a growing demand in utilization of eastern cottonwood by the local industries. For this reason, extensive researches are in progress, in Iran, on the properties and applications of this species. This species has low amount of mechanical properties so its densification might improve its properties. For this research, 15 healthy standing trees of eastern cottonwood were selected. The trees were randomly selected and the diameter of stems at the breast height was between 25 and 35 cm. Then the logs with 180 cm length were cut from the breast height following by conditioning with room temperature for 60 days. The primary 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 at 3 temperature levels, 120, 140 and 160 was used for this purpose. Then, the final specimens were cut with dimensions 50 cm by 50 cm and 20 cm in thickness. The results showed that the percentage of densification may significantly influence the density of samples, especially at the higher percentage (0.370 gr/cm3 for the control sample and 0.740 gr/cm3 at the 50% percentage). Furthermore, it was found that the amount of densification has significant influence on the withdrawal strength of nails (up to 200%) and screws (up to 140%).