高温中花旗松结构材顺纹抗压强度试验研究

To determine the effects of elevated temperatures and heating duration on moisture content, density and parallel-to-grain compressive strength, a total of 140 Douglas fir wood specimens was tested in nitrogen condition. The temperature was ranged from 20℃ to 280℃. Scanning electron microscope observation was employed to reveal the mechanism of high temperature on the reduction of physical and mechanical properties. Test results show that moisture content, density and parallel-to-grain compressive strength nonlinearly decrease with the increase of temperature. Moisture content and density decrease, and there is no obvious change in colour because of the release of moisture in wood material below 130℃. However, compressive strength decreases according to the glass transition temperature, and then increases with the reduction of moisture content. When the temperature is not higher than 190~220℃, moisture content further decreases, and chemical component begins to be thermally degraded. So, density, moisture content and compressive strength decrease, and wood colour begins to be deepened. There is an obvious increase in wood colour, and a rapid decrease in density and compressive strength occur because of the pyrolysis, when the temperature is higher than 220℃. Scanning electron microscope observation reveals high temperature contributed to microstructural damage. The porosity of cell walls in early wood grows more clear, and the thickness of cell walls in latewood becomes thinner after thermally treated.