高温中花旗松结构材顺纹抗压强度试验研究

Experimental study on parallel-to-grain compressive strength of structural Douglas fir wood exposed to elevated temperatures

在有氮气、温度为20~280℃和受热时间不同的条件下,对140个花旗松试件的含水率、密度和顺纹抗压强度进行试验;采用扫描电镜揭示高温对木材性能劣化机理.结果表明:木材物理性能和顺纹抗压强度均随着温度升高而非线性降低;当温度低于130℃时,受内部水分释放影响,含水率和密度降低,材色无明显变化,抗压强度由于玻璃化转变温度而降低,且由于含水率降低而增长;当温度为190~220℃时,含水率进一步降低,化学组分开始热降解,其密度、含水率和抗压强度降低,材色开始加深;当温度高于220℃时,木材热解导致颜色急剧加深,密度和抗压强度迅速降低;高温后木材中早材细胞壁多孔性更加突出,热解引起晚材细胞壁厚度变薄,使木材顺纹抗压强度降低.

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 from20℃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.