核桃楸木材的自由干缩特性

The Free Drying Shrinkage Characteristics of Juglans mandshurica Maxim.Wood

木材在干燥过程中因失水而导致干缩,非均匀干缩会产生应力限制木材的自由干缩。以核桃楸为试验对象,研究了5 mm厚(纤维方向)分层试件和未分层(整体)试片的自由干缩特性,并对比研究了受限干燥后木材的分层自由干缩特性。研究结果表明:室温下各层自由干缩系数和绝干干缩率存在显著差异,总体呈现表层向芯层递减的趋势,第1层自由干缩系数(0.254)最大,第7层自由干缩系数(0.165)最小。树皮侧木材的自由干缩系数大于髓心侧。整体自由干缩试件常温干燥过程存在由含水率梯度引起的应力,限制其自由干缩,其弦向干缩率比分层自由干缩试件小0.50%。泡水和汽蒸无法使受限干缩木材的塑性变形完全恢复,利用这种方法测量木材的自由干缩应变不准确。室温下弦向各层自由干缩的干缩率-含水率回归方程的决定系数(R^(2))均高于0.96,利用该方程可以准确计算各含水率点的木材自由干缩应变。

During the drying process,wood undergoes shrinkage due to water loss,and non-uniform shrinkage can generate stress that restricts the free shrinkage of wood.Juglans mandshurica Maxim.was selected as the experimental object to study the free shrinkage characteristics of 5 mm thick(fiber direction)layered specimens and unlayered(integral)specimens,and compared the layered free shrinkage characteristics of wood after restricted drying.The research results showed that at room temperature,there are significant differences in the free shrinkage coefficients and absolute dry shrinkage rates of each layer,generally decreasing from the surface layer to the core layer,with the largest free shrinkage coefficient(0.254)in the first layer and the smallest(0.165)in the seventh layer.The free shrinkage coefficient of the bark side wood is greater than that of the pith side.In the process of ambient temperature drying of integral free shrinkage specimens,stress caused by moisture content gradient limits their free shrinkage,with a shrinkage rate in the tangential direction 0.50%smaller than that of layered free shrinkage specimens.Immersion in water and steam cannot fully restore the plastic deformation of restricted shrinkage wood,making it inaccurate to measure the free shrinkage strain of wood using this method.The determination coefficient(R^(2))of the regression equation of shrinkage rate-moisture content for each layer in the tangential direction at room temperature is higher than 0.96,and this equation can accurately calculate the wood’s free shrinkage strain at each moisture content point based on the regression equation of each layer.